THE USE OP COBALT-60 AS A RADIOTRACER

IN A STUDY OP THE ANALYTICAL CHEMISTRY OF COBALT

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of the Ohio State University

By

DARNELL SALYER, B. S.

The Ohio State University 1956

Approvec by:

Adv^rer

Department of Chemistry ACKNOWLEDGMENT

The author would like to express his sincere appre­ ciation to Dr. T. R. Sweet for his guidance and advice during the period of this research.

The author’s wife, Octavia Elizabeth Salyer, has been a source of help and encouragement during the con­ clusion of this work and the oreparation of the manuscript.

Most of this work was completed while the author held graduate fellowships from the Cincinnati Chemical vVorks (1954-55) and the Central Division of the Allied

Chemical and Dye Corporation (1955-56). The aid provided by these fellowsnips is gratefully acknowledged.

ii Table of Contents

Page

INTRODUCTION ...... 1

THE ANODIC DEPOSITION PROBLEM...... 9

Theory of Anodic Deposition ...... 9

Conditions for the Deposition of C o b a l t ...... 13

Promising Methods, A Qualitative Study...... 16

Reproducibility, A Quantitative Study ...... 17

Nature of the Deposits...... 27

Ignition of Deposits...... 33

Summary of Optimum Conditions for Plating and Weighing...... 34

Preparation of the Standard Curve ...... 37

Interference Study...... 41

DETERMINATION OF SMALL AMOUNTS OF COBALT BY THE ISOTOPE DILUTION-ANODIC DEPOSITION' METHOD . . 4 6

Separation of Cobalt from Iron...... 49

Conclusion...... 49

A STUDY OF THE CATHODIC ElECTRODEPOSITION METHOD FOR oOBALT »»»»»••••»»»..»»•».»• 31

Previous W o r k ...... 53

Experimental. Examination for Residual Cobalt. . 55

Measurement of the Rate of Deposition...... 61

Explanation of Results...... 68

A Test for the Formation of Surface Compounds . . 73

Determination of Residual Cobalt. » ...... 76

S u m m a r y ...... 79

ill Table of Contents (cont’d)

Page

THE PRECIPITATION OP COBALT AS COBALTINITRITE...... 81

The Reaction...... 82

Interfering Elements...... 83

The Rate of Precipitation of Potassium Cooaltinitrite...... 84

Measurement of Rates...... 86

Procedures...... 87

Results and Discussion...... 89

Other Studies of Cobalt Precipitation ...... 100

Pot as slur Determinations...... 109

S u m m a r y ...... 112

SOLUBILITY LOSSES DURING GRAVIMETRIC DETERMINATIONS. . 116

The Potassium Cobaltlnitrite Separation ...... 116

The Double Ammonium phosohate Method...... 122

RADIOMETRIC TITRATIONS ...... 129

Previous v.ork...... 129

Experimental...... 130

Discussion...... 133

Results of the Study...... 135

Conclusions...... 140

THE SOLUBILITIES OP COBALT ANTHRANILATES ...... 142

The Measurement of Solubilities ...... 143

Exoerinental...... 144

Results...... 152 iv Table of Contents (cont'd)

Page

SUMMARY...... 158

APPENDICES...... 160

BIBLIOGRAPHY ...... 189

AUTOBIOGRAPHY...... 197

v List of Tables

Number Page

1 Comparison of Plating Methods ...... 13-19

2 Reproducibility Study I ...... 21

3 The Use of Sand-Blasted Anodes...... 22

4 Reproducibility Study II...... 24

5 Reproducible Deposits ...... 26

6 Deposits from a Bicaroonate-HgCO^ Buffer. . . . 28

7 A Titration Method for Per Cent Co In D e p o s i t s ...... 32

8 A Check for the Codeposition of Sodium...... 36

9 Preparation of the Standard Curve ...... 39

10 Determinations After Separations. Interference Study...... 43

11 The Analysis of Kickel Alloys and Steels. . . . 50

12 Conditions for the Electrodeoosition of Cobalt. 56

13 Results of Cobalt DeterminetIons by Several Methods...... 59-60

14 Calibration of the Apparatus Used In the Rate Stud ies ...... 65

15 Per Cent Cobalt Deposited vs. Tine of Electrolysis...... 65

16 Residual Cooalt In Solutions from the Rote Studies...... 66

17 Time Required for the Quantitative Deposition of Cobalt...... 67

IS Cobalt Losses during the ./ashing of Deposits. . 69

19 A Test for the Formation of Surface Compounds . 75

20 The Use of Spot Plate for Determining Cobalt in Electrolytes...... 73 vi List of Tables (cont'd)

Number Page

21 The Effect of Time on Cobalt Precipitation under Various Conditions. Volume Varied. . 90

22 The Effect of Time on Cobalt Precipitation under Various Conditions. Temperature Varied...... 92

23 The Effect of Time on Cobalt Precipitation under Various Conditions. The Amount of Cobalt Varied ...... 97

24 The Effect of Time on Cobalt Precipitation under Various Conditions. The Amount of KNOg Varied ...... 98

25 The Effect of Time on Cobalt Precipitation under Various Conditions. The Presence of Other Materials...... 101

26 Per Cent Cobalt Precipitated vs. Time. Kallmann’s Method. The Effect of Other Metals...... 102

27 Per Cent Cobalt Precipitated vs. Time. Kallmann's Method. The Amount of Cobalt Varied ...... 103

28 A Comparison of KNOg and KNOg + NaN02 as Reagents for Cobalt...... 105

29 The Kffect of Organic Liquids on the Precipitation of Cobaltinitrite ...... 107

30 The Precipitation of Dipotassium Sodium Cobaltinitrite in Potassium Determinations. Ill

31 The "solubility" of Potassium Cooaltinitrite in water at 25° C ...... 118

32 Losses of Potassium Cobaltinitrite on Washing with water and 10% Potassium Acetate ...... 120

33 Solubility losses of Cobalt in Cobaltinitrite Determinations...... 121

34 Solubility Losses of Cooalt in Determinations by the Double Phosphate Method...... 125 vii List of Tables (cont'd)

Number Page

35 Losses of Cobalt Ammonium Phosphate on Washing with Different Solutions .... 128

36 Radiometric Titration Data...... 136-137

37 Preparation of the Cobalt Compounds of Anthranllic Acid and Several of its Derivatives ...... 148-149

38 The Effect of Agitation Time on the Water Solubility of Cobalt Anthranilate at 25° C. 151

39 Standardization Data for the Active Cobalt Solution Used in the Solubility Studies • • 153

40 The Solubilities of the Cobalt Compounds of Anthranllic Acid and Several of its Derivatives ...... 154-155

viii List of Figures

Number Page

1 Drying Curve for Cobaltic Oxide...... 25

2 Standard Curve for the Anodic Deposition-Isotope Dilution Method. • • • 40

3 Apparatus Used in the Electrodeposition Rate S t u d y ...... 62

4 The Effect of Time on the Precipitation of Potassium Cobaltinitrite. Temperature Varied. . 93

5 The Decomposition of KNOg with Time...... 95

6 The Effect of Time on the Precipitation of Cobalt as Potassium Cobaltinitrite. The Presence of Organic Liquids...... 108

7 The Effect of pH on Solubility Losses of C0NH4 PO4 ...... 126

8 Apparatus Used for the Radiometric Titrations. . . 132

9 Radiometric Titration of Cobalt with l-NItroso-2-Naphthol...... 138

10 Radiometric Titration of Cobalt with 1-Nitroso-2-Naphthol. The Effect of Nickel. . . 139

11 liquid Counter Apparatus ...... 173

12 Response of the Liquid Counter ...... 177

ix INTRODUCTION

The purpose of this investigation is to obtain infor­ mation concerning the analytical chemistry of cobalt which will be of value to the analyst and the analytical chemist.

Radiotracer techniques are used in the study and in a broader 3ense the work will illustrate how radiotracer methods may be applied to analytical chemistry In general.

The development of new methods for the analysis of cobalt, a critical examination of some of the standard methods, and a study of certain problems which have plagued previous Investigators are Included in the present work.

1 2

Cobalt - Its History, Occurrence, Abundance and Uses

Although metallic cobalt was first prepared by Brandt

In 1735 and the first significant chemical studies were made

in 1802 by Thenard, the effects of cobalt, particularly its production of blue color In glasses and glazes, had been noticed and applied In early civilizations,1 Certain

poisonous effects suffered by mine workers are responsible for the name of the metal, supposed to be from the German

kobold, meaning goolin or gnome.

In a monograph on cobalt, Young2 has described in

detail Its geographical distribution, metallurgy, and uses.

The poisonous traits formerly attriQuted to cobalt are

largely due to arsenic, with which cobalt Is often assoc­

iated in nature. It is also found with varying amounts of

copper, nickel, iron, and sulfur. Cobalt ores, which rarely

contain more than about 7jb of the metal, are widely distrib­

uted geographically. Ma.ior deposits occur In Canada and in

North Africa. Because of the complexity of most ores, re­

covery processes are involved and expensive.

The aoundance of cobalt is 2.3 x 10~^% of the igneous

rocks of the earth.^ Although the element is rather rare,

the natural deposits are, fortunately, relatively concentra­

ted and accessible.

Cobalt Is an important constituent of high speed

steels, magnets, cemented carbides, and alloys. The Incor­

poration of cobalt in steels gives increased elasticity, 3 tensile strength, wear resistance and a better cutting edge for use at high temperatures. This is due chiefly to the presence of a carbide Co^C, which increases the temperature at which the iron-carbon phase, austenite, changes to mar- tensite.2 Other ferrous alloys include a variety of "Al- nico" magnetic cobalt alloys. Non-ferrous alloys include those of cobalt with chromium-tungsten and chromium-molybd- deum plus varying amounts of tantalum, vanadium and boron, e.g., "Stellites" and "Vitallium,H which are used for cut­ ting tools, exhaust valves in aircraft motors and diesel engines, nozzles, etc.

Cobalt is also used as a catalyst, in electroplating,

in the glass, ceramic and paint industries, and in soil treatment. Biologically, cobalt is one of the essential

elements, e.g., when there is a deficiency of the element in soils used for grazing purposes, the animals 3uffer harmful effects.^ Hence, small amounts of cobalt are used

in livestock lick3, feedstuffs and in pasture fertilizers.

There is 0.0H5 to 0.5 mg. of cobalt oer kg. in on­

ions, potatoes, soinach, lettuce, cress, tomatoes, apri­

cots, beans, wheat, corn, rice, etc.,1 ana tnere is thought

to De some connection between cobalt and vitamin B-^g.

The Chemistry of Cobalt

The strong interest in coordination compounds, the

demand for cobalt for use in steels and other alloys, and

the increasing interest in the cobalt content of soils 4 and biological materials has made the chemistry of cobalt important.

Metallic cobalt is a moderately strong reducing agent

and will reduce hydrogen ion while being oxidized to Co*2 .

The metal is prepared by carbon reduction of the oxides.

Oxidation states exhibited are 0, ■►I, + 2, +3, and +4. The

+1 and +4 are unstable and poorly characterized. In acid

solution only the *2 state is stable, but oxidation to the

+3 state is possible in neutral or alkaline media, especial­ ly If complexing groups are present.

Complex formation Is due to small cation size, rela­ tively large nuclear or Ionic charges, and favorable elec­ tronic arrangement. Cobalt III complexes are covalent and have orbital hybrid!zatlon3--sp5 , dsp2 , and d2 sp3. E° val­ ues show that complex formation stabilizes the +3 state.

Known cooalt oxides are CoO, Co.^O^, and C o . The

existence of the oxide CoOg is questionableCobaltosic

oxide, C03O4 , is prepared by heating cooaltous or cobaltic

oxides in air. C0 2 O3 prooably does not exist except In some

hydrated form (see however, pages 6 and 29).

Puval^ has shown that there are six po33ible cobalt

hydroxides. The colors are emerald green, brown or olack,

ultramarine, violet, dark rose, and pale rose. The dark

orown cobaltic hydroxide is somewhat similar to ferric hy­

droxide. 5

Cobalt as Co'1'2 Is very similar to Mi* 2 and separa­ tions of these two ions are difficult. Numerous chemical methods have been proposed. The most important procedures include the use of l-nitroso-2 -naphthol, dimethylglyoxime, potassium nitrite, and Ion exchange methods. Small amounts are easily separated Dy chromatographic methods. Commer­ cially, the difference in volatility of nickel and cobalt carbonyls is utilized for the separation.

Analytical Methods

Cobalt may be determined by gravimetric, volumetric, colorimetric, spectrographic, and polarographic means. Be­ fore the final determination it nay be separated from the copper group metals by sulfide precipitation, from iron by the use of zinc oxide, phosphate, or ether, and from nickel as indicated above.

Duval7 has made a study of several of the gravimetric methods with respect to the weighing forms. Many reagents, although satisfactory for the separation of cobalt from other metal3 , do not give good weighing forms and must be ignited or otherwise converted to a suitable form. ,'veighing as the metal or the sulfate Ip usually recommended; results obtained when oxides are U 3 e d are often in error by 1 or 2 per cent. According to Ephraim et al.»^ "The range of existence of C03O4. is more restricted than that of the cor­ responding oxide of manganese, and it is therefore less re­ liable for analytical purposes unless the temperature to 6 which It is heated Is carefully regulated." Some organic

compounds apparently form CogOj, while others form C0 3 Q4

during ignition*? At ignition temperatures above 1000° C*

both oxides are converted to CoO. Duval particularly rec­ ommends the anthranilate as a good form for weighing*

The electrolytic method is oerhaps the most impor­

tant gravimetric method and is discussed in a later section.

See Aopendices I and II for a list of organic and inorganic

reagents used in gravimetric work.

Volumetric methods for cobalt are based on reduction,

oxidation, complex formation, acid-base, and precipitation

reactions. The end point of the titrations has been deter­

mined by pot entiometric , polarographic, amperometric, conduo-

tometric, and visual means. Some of the most Important

methods and references to recent work are listed In Appen­

dix III. The precipitation titrations shown are of Inter­

est since they o \‘f er the possibility of emoloying a radio-

metric method for detecting the end point.

For routine determinstions of cobalt, colorimetric

methodr. have been most widely used. The principal reagents

are thiocyanate and aitroso-R-salt. Cobalt as the blue

thiocyanate complex may be extracted by organic solvents and

simultaneously separated from most common elements, inclu­

ding nickel. The use of nitroso-R-salt (dlsulfonated

l-nitroso-2 -naphthol) deoends on the great stability of the 7 cobalt III complex as compared with those of other metals.

There has been some question as to the correct wave length to use for spectrophotometric purposes.^

Many of the organic reagents used for cobalt separa­ tions and gravimetric determinations may be used for color­ imetric work when they can be extracted Into organic sol­ vents. DImethylglyoxlme becomes a good colorimetric reagent for cobalt when used in combination with other reagents, e.g., benzidine and o-toluidlne with organic solvents.

Important colorimetric reagents for cobalt and references to recent articles are listed in Appendices I and III.

Spectrographic analysis may be U3ed in determining

0.005 to 0.1 per cent cobalt. Cuta and Rauscher^0 gave

2378.6 X as the cobalt line most useful in the determin­ ation of cobalt in nickel salts. Standen1^- listed the elements which interfere and gave some of the most sensi­ tive lines when a zinc matrix is used.

Malyuga*^ reported polarographic determinations of cobalt In volcanic matter, soils and natural waters follow­ ing preliminary separation from other metals. The use of the polarograph in amperometric titrations of cobalt was illustrated by Kolthoff and Langer.l^

Cobalt-60

Naturally occurring cobalt consists of only one isotope, cobalt-59, which upon neutron activation becomes isotope 60. The latter is produced in two Isomeric states, 8 one of which has a half life of only 11 minutes and soon decays, while the other Is a beta-gaxnma emitter with a long half life of 5.3 y e a r s . 14 The beta particle energy Is

0.31 mev and the gamma radiations are 1.332 and 1.171 mev.

These properties, long half life and high energy radiation, are desirable properties for an isotope that is to be used in tracer studies. Decay corrections need not be Trade very often and the radiations are easily de­ tected. Moreover, because cooalt-59 has a favorable ther­ mal neutron capture cross section (23 barns) and is the only natural cobalt Isotope, cobalt-60 is available at a low cost. THE ANODIC DEPOSITION PROBLEM

The objective of this work was the development of a method for the quantitative determination of cobalt In which this metal la deposited electrolytically as an oxide on the anode. It was felt that this would make possible the simul­ taneous separation and determinatIon of cooalt in the pres­ ence of elements that interfere with the cathodic deposition or other determinations. In view of the difficulty of quan­ titative deposition of cobalt as the oxide, the isotope dilution method of analysis should be particularly advan­ tageous •

Cobalt is one of several elements that may oe depos­ ited anodically. Other elements that show this property are manganese, nickel, molybdenum, palladium, silver, thallium, lead, bismuth, polonium, and uranium. The higher insoluble oxides which are formed by anodic deposition all belong to elements having at least two oxidation states of which the lower is the more stable.^

Theory of Anodic Deposition

There are no definite statements In the literature as

to the mechanism of anodic deposition of cooalt. Wernicke^-®

indicated only that the oxide deposition occurred in prefer­

ence to oxygen evolution, I.e., oxygen is not liberated, but reacts with metal In solution to form a compound at the

anode. This may be true for cobalt in alkaline solution

9 10 where oxygen la more likely to be evolved. Wernicke16 gave as the order of ease of deposition from metal salt solutions: sliver and lead^ manganese and bismuth^ nickel

and cobalt^ palladium. Coehn and Glaser17*1® were of the opinion that the deposition Is due to the discharge of a complex Ion and suggested dating from hot solutions.

Saxon19 reports that electrolysis of a solution of KgS04

and C0 SO4 first deposits tiny ruby crystals of Co(0 H)g

and later brown Co(OH)^ which Decomes black CogO^ on heating. Glasstone and HIckling2® quote Grube and

Feucht6 when they give three stages for oxidation of

Co11 at a platinum anode in strong alkali:

at 25° C. 1. at +0 . 02 v. Co^04 is deposited.

2 . at-t- 0.11 v. apoarently CogOj is formed.

3. at-f 0.7 v. oxygen is evolved, a solid solution of CoOg in COgO- is probably formed:

iOg GogO^ 2Co0 g

Tubandt21 reports that GoO is the oroduct when glycerin is

oresent during electrolysis of strongly alkaline cobalt

solutions.

The mechanism for the formation of the nigher oxides

of lead, manganese and oolonium has been studied and the

mechanism of cobalt deposition is probably similar to that

for tnese metals. Nichols^S showed that Pbll does not

migrate toward the anode as a negatively charged ion. In 11 agreement with Classen,23 his work Indicated that an Ion such as PbOg* was probably formed and discharged after lead Is first brought to the anode by diffusion or by mech­ anical means. (Grube and Feucht3 plated cobaltlc oxide from a strongly alkaline solution which they state con­ tained CoOgs or HCoOg” .) Earlier studies had suggested that ?b^* is first oxidized to Pb*? which reacts with water to form Pb(0H )4 or hydrated PbOg, and the same was thought to be true for manganese. Negatively charged col­ loidal particles of the hydrated oxides were then depos­ ited on the anode as a result of electrophoresis.24,25,26

With regard to the deposition of polonium, Haissinsky has proposed several possibilities for the formation of

P0 O3 depending on the conditions.2? For acid solutions he gave the following:

Po03= +• + HgO = Po05 +■ 20H”

Po0+2+ + HgO = Po03 + 2H +’

Po+4 +i0 2 + 2HgO = Po03 + 4H*

?o {X0z )6= + $02 +2E20 * Po03 + 4H+ + 6N03"

In basic solution Po0 3s is simply discharged:

Po0^s = P0O3 + 3e“

Another plausible explanation of the reaction is in

terms of hydroxide soluoilities. Although in approximately

neutral solutions the solubility product of cobaltous hy­

droxide is not exceeded (K3p 2.5 x 10”-3-3), when Co+2 is 12 oxidized to Co+^ there is sufficient OH* present to exceed the Kap of cobaltic hydroxide (Ksp= 1 x 1 0 “45).

As deposition proceeds the layer of oxide increas­ ingly Insulates the anode to the point where no further deposit appears. Isotope exchange studies have shown that an equilibrium then exists between cobalt of the solution and the deposit.^® Oxygen evolution and rapid anodic deposition tend to reduce adherence by decreasing the density of deposits.

Although Glasstone and Hickling^0 have theorized that HgOg is an intermediate in many anode oxidations, pQ recent experimental findings of Haissinsky and Cottin*® indicate that this is not true for anodic deposits of nickel, cooalt, manganese, silver, polonium, or lead on platinum. According to these workers, it is hardly pos­

sible to admit a general mechanism for different anode processes; experimental facts show the necessity of giving

a mechanism for each case.

It might be mentioned here that not only may the mechanism vary according to factors such as the composition

of the solution, but that the product may vary in nature

as well.

In conclusion it can only be said that the mechanism

of cobaltic oxide deposition may be given by one of the

following equations: 13 2Co+2 + £0 g + 2HgO ^ COgOj + 4H +

Co+2^ Co+3 + e" and 2Co+5+ 3 HgO ^COgC^-t- 6H + for neutral and acid solution, and for basic solution,

Co+2 +- 4 0 H “ ^ CoOg"2 (or HCoOg") + 2HgO

2Co02“2+ HgO Co203 + 20H"+ 2 e“

After one of the reactions occurs, colloidal par­

ticles may form which are probably something like

(Cog03 #xHgO)0H~ (if cobalt is similar to iron in form­

ing a colloidal particle with a negative charge^). When

these are attracted to the anode, the negative charge which had stabilized the colloidal particles is neutralized,

diminishing mutual repulsion between particles and allow­

ing coalescence with consequent precipitation.

Conditions for the Deposition of Cobalt

Under certain conditions cobalt can be made to de­

posit anodically from solutions in the oH range 1 to 14:

a. Moderately Acidic Solution

Deposits were made from hydrofluoric acid solutions

by Skirrow^ and from a solution of cobalt sulfate con­

taining ammonium fluoride and nitric acid by Smith and

Lukens.52 The oxidation is favored by the conditions for

high oxygen overvoltage that are found in acidic fluoride

solutions. Unless the potential is maintained the oxide

tends to redissolve. In acidic solutions containing sul­

furic acid, cooalt is oxidized but not deposited as oxide,33 14

b. Weakly Acidic and Neutral Solution

Torrance34 deposited cobaltic oxide from a solution of pH 5 (acetic acid-acetate buffer) at elevated temper­ atures. Coehn and Glaser18 plated from neutral or slightly acidic solution, as did Saxon.^

c. Basic and Strongly Basic Solution

Since cobaltous ion tends to precipitate as hydrox­ ide in basic solutions, provision must be made to keep it in solution as a complex ion that may be discharged on the anode. Examples of this are uaown by the experiments of

Wernicke18 and of Muller and Spitzer3^ who U3ed alkaline tartrate and oxalate solutions to effect deposition of co-

Dalt and nickel oxides. In caustic alkali solutions, e.g.,

8 N KOH, cobalt hydroxide dissolves forming CoOg= or HCoOg- as a blue solution from which anode aepo^Its may be ob­ tained. Alkaline solutions containing Go4^ as complex ions tend to be unstable to air oxidation and have no particu­ lar advantage over neutral or slightly acidic solutions when used for anodic deposition; moreover, there is also a

strong tendency for cathodic deposition of metallic cobalt from alkaline solutions.

Of the three cases In which cobalt was reported to

be deposited quantitatively, the most extensive study was

that of Goehn and Glaser.18 They were able to effect a

separation of cobalt and nickel by anodic deposition, o ut concluded that this is useful chiefly for qualitative tests 15 since long periods of time, a controlled anode potential* and low current densities were required for quantitative deposition. Some determinations necessitated the use of ten platinum anodes (5 x 9.5 cm.) which were used success­ ively over a twenty hour period In which 0.08 grams of co­ balt plated as oxide.

Smith and Lukens®2»36 satisfactorily plated cobalt as oxide from cobalt salt solutions containing four grams of ammonium fluoride plus two ml. of concentrated nitric acid and 0.1 to 0.2 gram of cobalt in 100 ml. of solution. At

85° and using 4 volts, deposition of the oxide on a sand­ blasted platinum dish anode was complete in two hours.

This method has the disadvantages that the deposit Is not very adherent and the use of hot solutions containing HP

Is not very desirable. Apparently no studies were made with nickel present.

Torrance^® reported good results for cobalt in nick­ el alloys by a double anodic deposition at pH 5 and 95° using the Sand revolving diaphragm electrode. The metal­ lic cobalt-nickel deposit ootained In routine analysis was stripped and the cobalt plated as oxide, redissolved and replated; no more than forty milligrams of cobalt could be determined In this manner because of deposit non-adherence.

The plates were weighed f,as Co^O^", but unfortunately no mention was made of the means of drying deposits. 16

The present work included a brief trial of each of the previously mentioned methods of anodic precipitation of cobalt plus a few other trials under slightly different con­ ditions. Included also was a study of deposits obtained from certain buffer solutions in the vicinity of pH 7.

Reproducibility should be more easily ootained from such solutions.

Promising Methods, A Qualitative Study

Variables determining the type and quality of cobalt oxide deposits include: temperature, time of electrolysis, cobalt concentration in the elating bath, condition of the platinum anode, pH, voltage maintained, and effects of other substances present during elating. For this study, the first four variables were held constant. They were: (1) temperature--20° C.; (2) time--20 minutes; (3) concentra- tion--10 mg. of cobalt/50 ml. bath; and (4) smooth platinum anodes. The remaining variables were fixed oy the partic­ ular method from the literature or were determined oy the buffer system used.

Procedure. Ten mg. quantities of cobalt containing tracer were added to each of several solutions that were pre­ pared as described in the literature (references in Table I).

With the platinum disk anodes in place, each was electro- lyzed for 20 min. In a modified tower electrolysis cell.

They were rinsed in double distilled water, air dried and counted. The physical nature of the deposit and the be- 17 havoir of the solution during plating were noted.

Results - Table 1. Of the first six experiments, the best appearing deposit was that of experiment 3 , the method of Muller and Spitzer (slightly modified since the cobalt concentration was reduced). Not only was this de­ posit superior in appearance, but it also contained the most cobalt. Uniformity and adherence of the oxide and the condition of the solution and cathode after electrol­ ysis were all satisfactory, therefore the initial studies on reproducibility were made on plates from alkaline tar­

trate solution, However, deposits from certain buffer

solutions, oicarbonate and borate, also appeared to oe

quite good.

Reproducibility, A Quantitative Study

Two measureable quantities indicated reproducibility:

(1 ) the specific activity of anode deposits obtained under

the same set of conditions; and (2) the per cent cobalt

in the deposits. The latter value is found by activity

measurements or indirectly by a titration mentioned later.

jVhen activity measurements were used, the per cent cobalt

was calculated by the following equation:

% Co _ specific activity of oxide specific activity ct metal x

The same active cobalt was used in preparing both metal

and oxide deposits on the same type of disk electrodes.

Identical geometry conditions were used in counting. Table 1

Comparison of Hating Methods3- axp’t joaposHuon Jo script ion Be havoir Cathode ho. of Delation Voltage of deposits During rlatin; Deposit hef.

l*L'5 p. • • r,>e7 3.3 very thin, no chan ;c none 13 reo-brown

pd ..1 * 3t!,) . - cCi : non-adherent solution ciianped slight 5* 21 uark brown to xron deep blue to bluCK gray, black sus­ pension

3 O.p ‘•Z'JLr--^G i.O go on and unu- solution turned none 16, 35 5 -TL* 3b,- hue! i'or..:, jet yellow-yecji to . ’ ' 1 ’V -f tan

Jv.- . JL. 3b,- -ai. .:ou-uiaforci no change, de- yes 1 ;.JL, glycerin - :\n.Ti co.i ositio.: on sta.ic.in

r , , i: -.} •1 to no deposit no cuange yes, 34 dai’k ■J a.Op g»‘■'^>^■'2.^7 2.3 black, Tons no canape none 13 »*,' • _j « . ^ O’V-

7 r_, - JL * L- # J. - • »

H CD Table 1 corrt'd

Comparison of Plating Methods3,

:p’t Jo...position Description bokavoir Cathode .0. oi ojl..*t ron .olaage of de jo sits Durinr Tlatin- Deposit fief.

j 3 .!• G.l i. -Ovj• i 1-2 ■ - -. f * ■ ! no change none 25 .a. o.i ;; k3jo3 brov/n-black ^ ? 1 * “ ^ oG y j1 ^ i I • fairly adherent

9 i.a2CG3 to neutral 11.; ao good block solution turned none o.t •. cue ess deposit, very light preen, adherent opt on standing 15 • in.

The following factors affect in.-: the type and quality of deposits were held constant

tiiroughout this st .ay; temperaturc, 25° 2,; deposition tine, 20 . inutesj amount of cobalt

used, Id ;ng. as the sulfate; volume of plath.y bath v;as 50 nil.; smooth platinum anodes

were used.

to 20

Procedure. Several deposits were prepared as In

Expt. 3, Table 1* They were dried Tor one hour at 70° or

100° C., weighed, and the activity measured. Metallic

plates were prepared from the same active cobalt mixture

(deposited from an ammoniacal solution); these were sim­

ilarly dried and counted.

Results. The values of the specific activity of the oxide and metal deposits and consequently the per cent

cobalt were calculated and are shown In Table 2. The re­

producibility is shown to be not quite satisfactory for

quantitative work, although the variation is not large.

It was hoped that deposition of heavier deposits and at­

tempts to attain better drying would lead to more consis­

tent results.

The deposition of larger amounts of oxide is a prob­

lem In Itself. When attempts were made to get deposits

weighing more than about one milligram by performing the

ele ctrolysis for longer periods of time or by using sol­

utions containing a greater cobalt concentration, the de-

oosit became non-adherent to the smooth platinum anode.

Much better adhesion was obtalne d when sand-olasted anodes

were used. See Table 3. Since the backseattering of ra­

diation and thus the counting rate Is affected by this type

surface, the sand-blasting had to be uniform. An alterna­

tive to sand-blasting would be platinizing. 21

Table 2

Reproducibility Study I

Weight of Drying Specific Per x assuming Depo aits, Temp•, Activity Cent C o 2 ° 3 #jcH2°* Mg. °C. C./Min./Mg. Cobalt

2.624 (metal) 70 2410 100.0

0.752 (oxide) it 1045 43.4 5.40

ii it 0 . 435 1038 43.0 5.85

0.526 [i ii 998 41.3 6.07

5.174 (metal) 100 3831v 1.613 M II 3846^3839 100.0 0 .203 (oxide) II 2235 5g .0 2.05

1.044 tt II 1840 47.9 4.42

0.878 ti II 1950 51.1 3.66

0.973 it II 1974 53.6 3.04

0 .925 IT It 1889 56.2 3.12

0 .929 II II 1916 54.1 2.90

* Calculated from the per cent coon it. 22

Table 3

The Use of Sand-Blasted Anodes

Showing the weight of depositsin mg."**

Deposition Time, Min: 20 40 60

Mg. Co Taken: Anodes:

10 Smooth 0.973 0.925 0.929

Sand­ blasted 0.959 1.786 2,798

20 Smooth n.a.*:H* n.a. 2.613 heavy n.a.

Sand- olested 1.781 1.341 6.372

* All deposits made at 20° C., dried at 100° C. for 1 hour,

"n.a." means non-adherent. 23

Using the sand-blasted anodes, further thermal studies were made* Deposits were prepared as before and the following means of drying was attempted: (1 ) at room temperature in a desiccator over CaS0 4 , (2 ) at room temp­ erature in a vacuum desiccator over BaO, (3) at higher temperatures in an oven, and (4) in a muffle furnace. Re­ sults from these studies were no better than that shown in Table 4, where the deposits were dried at 100° C. The drying curve, Figure 1, shows either some difference in chemical composition of the three deposits used, or illus­ trates the fact that all were not dried to the same extent in the same period of tiwe.

In view of difficulties encountered in arying de­ posits at 1 0 0 ° C. or by ignition, it was decided to dry them at 40° C., which, according to Coehn and Glaser, has been done for MnC>2 deposits. At this point also, a change was made to the use of buffered solutions since they are more easily prepared and lend themselves to better reproducibility.

Drying at 40° C. of deposits made from boric acid- borate buffers at pH 7.5 - S.O showed good reproducibility,

as is shown in Table 5. The weighing form corresponds very closely to the formula CogOj-SH^O. In quantitative anal­ ysis, hydrous or hydrated oxides generally cannot oe dried reproducibly to constant weight at low temperatures; this

is thought to be possible for cobaltic oxide in the present 24

Table 4

Reproducibility Study II

Weight Deposits S.A- x assuming Mg. Dried at C ./Min./Mg. JibCo CogOs-xHgO

2.312 {metal) 1 0 0° c. 4414 1 00.0

1.672 {oxide) II 2310 52.3 3.3

1.755 ii II 2617 59.1 1.7

0.952 n It 2367 53.9 2.7

2.032 ii II 2407 54.7 2.6

1.146 n II 2414 54.9 2.5

2.24 2 it II 2475 55.9 2.3

1.431 n It 2606 59.0 1.7

1.429 it II 2364 53.6 2.8 Temperature 1000 400 600 200 800 0 - rig uv fr oatc Oxide Cobaltic for Curve Drying 10 e Cn Weight Cent Per i. i Pig. 20 30 Loss Loss 40 50 25 2 6

Table 5

Reproducible Deposits

Plated 40 min. from a solution buffered with boric acid and NaOH. pH 7.6, voltage 1.7, current 1-2 ma/cm2 , deposits dried for 2^ hours at 40° C.

'Weight of Activity S.A. Per cent Deposits Cobalt Mg. Counts/Min. C./Min ./Mg.

3.294 5438 1651 53.9

3.283 5426 1652 53.9

2.690 4373 1626 53.1

2.301 3Q67 1680 54.8

2 . 0 2 0 3316 1642 53.6

2.654 4331 1638 53.5

1.841 2991 1625 53.0

S.A. of metal was 3064 C Av. 53.68, r - 0.41 27 study because the product was prepared electrolytically in a very thin, uniform layer which lends itself to suitable drying.

Solutions buffered with bicaroonate-carbonic acid gave heavier and very adherent deposits, which, however, were not reproducible to the oesired degree. Table 6 shows the results for a series of plates prepared from this buffer. It is probable that conditions for reproduc­ ibility could be worked out which include use of this buffer rather than borate-boric acid, but the affinity of the deposits for COg must be considered.

The fact that some cobalt Is oxidized to Co^^ that

Is not deposited as oxide is evident In solutions contain­

ing bicarbonate. During electrodeposition, the solution changes to a light green color due to a caroonate complex of trivalent cooalt. This complex has been noted in pre­ vious electrolytic studies37 ana i3 probably Co{C0 3 )”3 or t 38 CotCG^Jg • Some cobalt may remain In solution as a trivalent complex when other solutions are electrolyzed

ps well.

Nature of the Deposits

The properties of freshly formed deposits are as

follows: the color is black to blue-black and it becomes

dark brown upon air drying; the deposit is In the form of

a gelatinous layer uniformly distributed on the disk.

Being gelatinous it has a relatively large surface and

great adsorptive jowers especially for certain gases, e.g., 28

Table 6

Deposits from a Bicarbonate-^CO-j Buffer

Plated for 45 min. at 1,2 v. Dried at 40° C, for 2^ hrs.

Weight Net S,A. Per Cent Deposits Activity CoDalt Mg, C./Min. C./Min./Mg.

1.931 3094 1602 52.2

3.797 5669 1491 48.7

3.989 6014 1508 49.1

3.655 55 62 1522 49.7

2.052 3430 1672 54.5

1.952 3235 1658 54.0

S.A. of metal was 3064 C,/m ./Mg . Av. 51.3,

CO and COg;^® It can be peptized as is true with many hydrous oxides.4' The composition of the deposits that were plated at room temperature and air dried ten minutes

(see also Figure 3) is approximately CogO^SHgO, while the number of molecules of water Is decreased to about three

In deposits dried to constant weight at temperatures up to aoout 75° C. Drying at higher temperatures decreases the amount of water until oxygen is also lost as is Indicated below. ./hen deposition was made from solutions at temp­ eratures above room temperature and up to 90° C., deposits air dried at room temperature contained three molecules of water per mole.

Numerous studies of the behavoir of cobalt-^^ oxide or cobnltic hydroxide with respect to dehydration have

been made .^9 »4^ »4^ indicate that it is difficult, If

not impossible, to dehydrate CogC^'xhgO to CogOj. Actually

there is some question as to the form of the precipitated

compound. By means of X-rays, Natta and btreda4^ studied

preparations obtained in various ways (not electrolytic)

having compositions varying between CogO^'SHgO to 0 0 ^0 3 ,

and concluded that the gel is the hydrouc oxide, Co203 ,

which loses oxygen at 265° C.:

3 CogC>3 ^°3^4 ^

Huttig and Kassler44 however, say that it is a hydrous monohydrate which loses water and oxygen simultaneously

rt 143-157° C.: 30

3CogO

In the present work It was not necessary to know which, If either, cf these is the actual form of electro- lytically prepared oxide since the drying form most easily obtained is certainly not either the anhydrous oxide or the monohydrate.

In the literature Cog0 3 *xHg0 is generally listed as being black In color,^9 -the statement is made that any brown color that is present is due to cobaltous oxide.

However, in the present work it was shown that even the

Drown deposits that remain after long standing in air

(2-3 days) contained most of the cobalt as C o ^ 1 . This was done by placing the disk In aqueous KI solution, add­ ing HC1 then titrating the iodine liberated with 0.01 H sodium thiosulfate. The reaction Involved Isi

Co2°3*xH2° + 2 1“ + 6 H+ ^ 2 Co+2 +- I2 +(x+3)HgO One equivalent of iodine is produced for each mole of co­ balt reduced.

Titration Procedure. A sample (on disK) was placed

Ina clean dry 100-ml. beaker, 1.5 ml. of water and 0.1 g. of solid K.I were added and the solution was swirled to dissolve the KI. Two drops of concentrated HC1 were added

and mixture was swirled again until the deposit dissolved.

This was Immediately titrated to the last faint trace of

yellow Ig, starch Indicator was added and the titration was

completed. The total volume was kept at a minimum to in­

crease the sensitivity of the end point. The 0.01 N ^a2^2^3 31 solution was prepared by dissolving 2,5 g. of the penta- hydrate in double distilled water, adding 0*01 g. NagCO-j,

and diluting to one liter. After standing overnight, it was standardized against IkgCrgOy as primary standard. The

solution was delivered from a 10 ml. microburet.

The titration method is of limited accuracy for

determining such small amounts because of the necessity of using very small volumes and because of a possible small

error due to air oxidation of iodide. However, the data

for per cent cobalt in several samples as given in Table

7, are sufficient to show fair agreement with the findings

by activity measurements. Average values of a series of

measurements show 51.4% by titration methods compared to

53.6% by the activity measurements (Table 5). "Brown"

deposits, those which changed to a brown color on standing

in air for 2-3 days or more, show that as much as 90% of

the cobalt is still in the higher oxidation state. Deposits

used in quantitative determinations in the present work

were not allowed to stand in air for such long periods

before weighing. If such deoosits are used the results

are slightly high.

Another important point proved by these titrations

is that cobalt is actually in the +3 oxidation state.

Previously the hydrated sesquioxide formula was only as­

sumed and the activity measurements gave no proof of the

oxidation state. 32

Table 7

A Titration Method for Per Cent Co in Deposits

Weight Deposits Weight Cobalt Indicated Per Cent Mg. by the Titration, Mg. Cobalt**

Freshly prepared deposits, black:

0.735 0.387 52.8

2.047 0.978 47.8

1.010 0.525 52.2

0.845 0.432 51.1

1.310 0.660 50.5

0.596 0.326 54.7

1.144 0.581 50.8

0.881 0.434 49.4

0.933 0.497 53.2

Deposits which otood in air for 2-3 days, brown:

0.864 0.408 47.4

0.832 0.402 43.4

1.120 0.657 44.6

* The rean value for freshly prepared deposits was 51.4^ with c'sl.V/S absolute. 33

Ignition of Deposits

Occasionally it is helpful to ignite anodically formed oxides to convert to a more suitable weighing form.

This has been done for manganese, which is ignitea to

Mn3°4 * **or l«ad» which can be Ignited to PbO. E. P. Smith,^2 in the preliminary experiments mentioned earlier

suggested that the cobalt oxide should be Ignited to C0 3 O4 .

In experiments or determinations In which active

cobalt tracer is used, ignition has the disadvantage that

some cobalt diffuses into the metallic platinum anode

disks due to extreme thermal agitation at the Ignition

temperature. The platinum electrode is thus "contaminated"

with activity. Other disadvantages of ignition are, (1)

the fact that a considerable amount of weight is lost on

Ignition, i.e., up to l/3 the original weight of the de­

posit, and (2 ) the C03O4 remaining is difficultly soluole

even in concentrated acids.^

If the Ignition method were used, the ignited depos­

its of Co^O^ would have to be stripped with hot concen­

trated sulfuric acid, and the last traces of cobalt which

diffused into the platinum would have to be removed by

using hot concentrated sulfuric acid or aqua regia to dis­

solve part of the olatinum. For these reasons It was de­

cided to resort to ignition only if other possibilities

failed. 34

The good results obtained by drying deposits made frcm a plating bath buffered with boric acld-borate at

40° C. (see page 28 and Table 5), eliminated the need for resorting to ignition or to other roundabout methods such as indirect determination of the weight of cobalt by color­ imetric measurements on the solution ootained by dissolving the deposit after measuring its activity*

Summary of Optimum Conditions for Plating and jVeighing

The boric acld-NaOH plating bath (referred to pre­ viously) gave good, reproducible, high quality plates. Its composition was as follows: The final concentration of boric acid useo for buffering was 0.05 molar, enough sodium hydroxide was added to give the desired pH and the solution was made 0.025 M with respect to potassium sulfate. The latter tends to maintain ionic strength and t jrefore pro­ mote better buffer action, helps prevent peptization of the deposit, and serves as a suooorting electrolyte for the electrolysis.-*-® Adsorption or occlusion of sulfate by the oxide was negligible as might be expected when depos­

its are made from nearly neutral solutions.

The oH range found to be best for this elating bath was 7.7 to 7.9. Unfortunstely this is at the lower extreme

of the boric acid-borate buffer range, but the other common

buffers, phosphate, bicarbonate and organic buffer systems

were all unsatisfactory for reasons mentioned on cages 35

27 and 41* At pH's less than 7.7, deposition Is unneces­ sarily slow while at values greater than 7.9, the deposit is partially or completely non-adherent.

Cobalt should be present In the plating bath to the extent of 7 - 13 rag. per 50 ml. of bath. The reasons for this and a discussion concerning interference of other ions is given later.

A study of deposits made from a solution containing

Inactive cobalt but active Ha-24 tracer showed little occlusion or adsorption of sodium by the plates. See

Table S. It was presumed that potassium is like sodium in this respect.

Deposits dried at 40° C. for 2 to 2^ hours were reproducible and their composition closely approached

Cog0 3 *3 Hg0 as shown In Table 5. Consequently this temp­

erature and time of drying were used consistently during the study.

At voltages higher than 1.8 volts oxygen evolution

occurred and the buboles thus formed caused deposition to

cease, lead to "pinholes" in the deposits, or reduced ad­

herence; consequently, the optimum voltage range Is 1.5

to 1.8 volts.

Prolongeo electrolysis of the solutions yielded a

suspension of finely divided material, probably ColOH)^*

Air oxidation may have oroduced some of this. 36

Table 8

A Test Tor the Codeposition of Sodium

The plating bath contained 10 mg. of Inactive cobalt and a total weight of 35 mg. of sodium. Its volume was 70 ml.

The usual borate buffer was used.

S.A. Deposit S• A. Sodium11' Weight Ha In Deposit

12 C./M./Mg. 8080 C./M./Mg. 1.5 X 10"3 Mg.

w To obtain this value, 1 ml. of the plating bath was

evaporated to dryness In a petrl dish. This contained

1/70 x 35 mg. of Na or 0.5 mg. Its activity was 4040

C./M. and S.A. would therefore be 8080 C./M./Mg. The

disk w a s placed in a similar petri dish and counted

in the same manner so as to give the same geometry for

each count. 37

Preparation of the Standard Curve

The standard curve for the isotope dilution method

(see Appendix IV) was prepared after isolation of cobalt by anodic deposition as described above. Details concern­ ing the apparatus and chemicals used in this work are given in Appendix IV. The boric acid-potasslum sulfate buffering

solution was prepared with "analyzed reagent" grade chem­ icals and was 0.1 M in the acid and 0.05 M in potassium

sulfate. The 0.1 and 0.5 M NaOH solutions were prepared from "analyzed reagent" grade NaOH.

Procedure. A 10 ml. portion of the radioactive

cooalt solution was pipetted into each of a number of

different known volumes of the standard inactive cobalt

solution and mixed thoroughly. Twenty to 25 ml. of boric

acid-potasslum sulfate solution were added and 0.1 M NaOH was added dropwise with stirring until the oH was 7.6 to

7.8 as determined with a pH meter; then the solution was

diluted to 50 ml. with double distilled water.* The sand­

blasted platinum disk anode was cleaned in the usual manner,

dried for 15 minutes at 40° C, and weighed to the nearest

0.002 mg.** With the disk in place In the cell (see p. 10),

the active solution was introduced and the solution was

■a Small amounts of basic salts sometimes formed. They

were filtered off and discarded.

■JHt Oxide deposits were stripped in acidic (HC1) iodide,

oxalate or peroxide. 38

electrolyzed at 1.5 - 1.8 volts for 40 minutes with the

platinum disk as the anode. The still active solution was removed through the cell's glass side arm, the cell was rinsed with double distilled water, and the disk with

deposit was removed. The disk was washed with double dis­

tilled water and adhering water droplets were removed with

a piece of filter paper. It was dried in air until no water was visible, placed in a 40° C. oven for 2 to 2

hours, and weighed as before. The activity of the deposit

was determined by placing the disk in a planchet In posi­

tion in the sample changer and with a 70 mg./cm.2 aluminum

absorber in place. Coincidence, background and efficiency

corrections were made on the observed activity and the

specific activity was calculated. The data appear In

Table 9.

Results - Table 9 and Figure 2. For the standard

curve the weight of inactive cobalt taken was plotted as

ordinate against 104 /S.A. as absclssl. The factor 104

was introduced for convenience In plotting. At W values

less than about P mg. the smaller amount of deposit formed

In 40 min. deposition lead to some uncertainty. Similarly,

above about 15 mg. the activity of deposits obtained in

the usual electrodeposition time was low; this also led

to uncertainty or Inconvenience. Consequently the portion

of the curve between 6 - 15 or better 7-13 mg. 1b best Table 9

Preparation of Standaru Jurve

Ob served Jaci:- Coine. iiffic. lot Aeipht S.a. oxide 1/5 .A. x K A ■jo blit activity h; round dorr. dorr. activity Oxide Deposits / t T aken Deposits ■j . ^an. 1:,g. /Count/ Dy. d./:2n. C ./liin. 1*5 • per I>. Av. liin.

5.000 2054 40 15 0 2029 0.735 2755 2705 3.697 it 2699 40 23 0 2637 1.010 2655 f 7-500 1344 51 0 0 1299 0.653 1975 2001 4.998 11 1530 51 Q/ 0 1517 0.765 1936 11 1470 51 7 0 1426 0.693 2042

10.00 1352 40 6 0 1313 0.345 1553 1551 6.448 11 1047 40 3 0 1020 0.655 lr42 II 976 40 0 920 0.596 1552

12.50 1333 51 7 u 1344 1.098 1226 1220 3.196 11 945 51 4 0 397 0.751 1192 11 yio 51 3 0 363 0,700 1242

15.00 1236 43 3 0 1193 1.144 1055 1055 9.479 II /i j 43 5 0 935 0.331 1060 *-% It 943 43 ;> 0 911 0.364 1046

L-j * LA> uol 40 0 11 633 0.764 720 301 12.5 li ^99 .’0 2 11 672 0.332 312

0» <0 2000

18 00

16 00

14 00

12 00

10 00

8 00

6 00

400

2 00 Standard Curve for the Anodic Deposition-Isotope Dilution Method

0 100 200 300 400 5.00 6.00 700 8.00 900 1000 1100 12 00 x I0 4 (m g/count/m in) O 41 for most purposes and should be used if the approximate per cent cobalt in a sample is known.

Interference Study

It was desirable to know which ions or other sub­ stances interfere with cobalt anodic deposition. Ions expected to interfere were (1 ) cations which may be depos­ ited anodically— those of Mn, Ni, Pb, Mo, Pd, Ag, Tl, Bi,

Po, and U, (2) anions strongly adsorbed on hydrous oxides, e.g., arsenious acid, phosphoric acid,40 (3) substances which would reduce the deposit or otherwise interfere with the main reaction, such as HgOg, organic anions and acids,4®

(this explains why organic buffer systems cannot be used in the preparation of the plating bath), and, (4) other

substances known to Interfere in anodic deposition of other elements, specifically mercury, chromate and phos­ phate which Schrenk and Delano4^ report as inhibitors to the deposition of lead dioxide. Reducing agents such as

the halides should also be absent since they easily polarise

the anode. Anions that form Insoluble cobalt precipitates were not considered since they would hsve been removed

during the process of dissolving the sample.

Procedure for the Interference Study. Solutions of

metal Ions for the tests were prepared by weighing to the

nearest 0.01 grams, quantities of the nitrates, sulfates or

oxides, sufficient to prepare 100 ml. of solution contain­

ing 2 mg./ml. of metal. When oxides were used they were 42 initially dissolved in the minimum amount of sulfuric acid and then diluted. Five ml. portions were taken to supply

10.0 mg. quantities of metal, the amount used in each test.

Ten ml. of radioactive cobalt, 20 ml. of buffer, and 10.0 mg. of the metal to be tested for interference were added to 10 ml. of the standard cobalt solution

(10 mg.). Five tenths molar NaOH was added until a pre­ cipitate was formed ( or to 7.6 - 7.8 if no precipitate formed). The precipitate was filtered off on S & S black line filter paper. The pH was adjusted to 7,6 - 7.8 by

again adding NaOH and filtering further if necessary, and electrodeposition was carried out in the previously pre­

scribed manner. The specific activity was found as before

and the weight of cooalt was read from the standard curve.

The difference between 10.00 mg. and the value actually

found gave a measure of the interference.

Results. Tests for interference of the following

ions were made: nickelous, manganous, arsenite, ferrous,

ferric, cuprous, zinc, aluminum, silver, chromate, bis-

muthyl, potassium, sodium, magnesium, calcium, barium,

strontium, lead, mercuric, cadmium, 3ulfate, nitrate, and

small amounts of chloride. The data of Table 10 show that

the following Vons may be present during deposition and do

not interfere: sodium, not as slum, magnesium, chromate,

silver, bismuthyl, and cadmium. The cadmium and bismuthyl

were partly precipitated as the solution was buffered. 43

Table 10

Determinations after Separations. Interference Study.

Initial Composition of Solution 1/S.A. x 104 W, Mg. % Error

a. Non-Interfering Substances:

10.00 mg. Co 6.375 9.720 -2.8 10.00 mg. Co 6.520 9.980 -0.2 10.00 mg. Co + 10.0 mg. Pe 6.470 9.970 -0.3 it ■+ 10.0 mg. Cu 6.520 9.980 -0.2 ii + 10.0 mg. each 6 . 635 10.15 1.5 Of Fel Cu ii + 10.0 mg. Cr 6 .560 10.03 0.3 as Cr0^ = ii + 10.0 mg. Zn 6.580 10.07 0.7 !l +10.0 mg. Bi 6.450 9.860 -1.4 II +10.0 mg. Ag 6.580 10.07 0.7 II + 10.0 mg. Al 6.455 9.880 -1.2 Tt + 10.0 mg. each 6.720 10.30 3.0 of Ba, Ca, sr, and Mg it + 10.0 mg. P b 6.550 10.02 0.2 it + 10.0 mg* Cd 6.505 10.03 0.3

b. Interfering Substances:

mg. Co + 10.0 mg. Ni 6.940 10.69 6.9 rr + 10.0 mg. Ni 7.190 1 1 . 06 10.6 it + 10.0 mg. Mn 64.5 ca. 109 1000 ii + 10.0 mg. As 9.970 15.91 59 ii + 10.0 mg. Hg 7.455 11.56 15.6 as acetate n + 10.0 mg. Hg 9 .40 14.8 48 as oxide

c ,, Separation of Cobalt and Manganese by Cooaltinitrite Precipitation

mg. Co + 10.0 mg. Mn 6.589 10.10 1.0 (1 ppt'n) it + 10.0 m g . Mn 6.490 9.94 -0.6 (2 ppt'ns)

d. Separation of ^ooalt and Mercury by Use of Copper

10.00 mg. Co + 10.0 mg. Hg 6.700 10.28 2.8 as oxiae

Tfr at a pft of 5 and at 90° C., according to T o r r a n c e . 54 44

Since silver gives a non-adherent cathode deposit which formed a suspension in the plating bath, it is best to remove silver with a minimum of chloride before buffering*

Although chromate interferes in the anodic deposition of lead,4 7 it did not interfere here; in fact, Coehn^-7 added dichromate to cobalt solutions before anodic deposition in order to increase the cathodic hydrogen overvoltage.

During the buffering process iron was precipitated as ferric hydroxide at a pH of 3.5; cuprous, zinc, alumin­ um, and chromium III ions were filtered off after they were precipitated at pH 6.5. Lead, the alkaline earths, and some silver were precipitated as sulfates and were filtered off. Ferrous iron strongly adsorbed cobalt and for this reason should be converted to ferric iron before buffering.

The quantity of metal or metals to be separated as hydroxides or sulfates during the buffering process is limited only by the fact that sufficient cobalt must remain unadsorbed in the solution to form a weighable deposit on electrodeposition. If amounts of these elements large enough to carry down most of the cobalt were present, double precipitations or another means of separation would be necessary.

Godeposited cations were nanganous and nickelous, manganous being by far the worse. Only a small portion of

the nickel, as compared to cobalt, was deposited. Another 45 means of removing nickel and manganese from cobalt-nickel mixtures must be resorted to before a single deposition

gives good results by the present method, Arsenite strongly

inhibits formation of a deposit. The small amount of de­

posit that doe3 form in the presence of arsenite has a

very low specific activity and therefore erroneous results.

The fact that arsenious acid is strongly adsorbed on hy­

drous oxides is the probable explanation.^ Since ferric

iron precipitated at pH 3.5 from a hot solution strongly

adsorbs the arsenic, the latter can oe removed from co­

balt-arsenic mixtures leaving most of the cobalt in an

arsenic free filtrate. Mercuric ion forms yellow HgO in

the solution during plating. The HgO is apparently occlu­

ded In the deposit. It is best to remove this ion with

metallic copper before carrying out the deposition. determination o p s m a l l a m o u n t s o p c o b a l t

BY THE ISOTOPE DILUTION-ANODIC DEPOSITION METHOD

To verify the analytical method for cobalt described in the previous chapter, some typical materials containing cobalt were analyzed. These were National Bureau of Stan­ dards samples of alloys and steels of varying composition.

The analyses involved isotope dilution, isolation of the cobalt from interfering constituents, and anodic deposition of the cobalt.

All the samples that were analyzed contained large amounts of nickel as well as some manganese. The method used in separating cobalt from these metals was the cobal- tinitrlte precipitation. The isotope dilution method allows shortening the usual 6-24 hours required for the quantitative precipitation of cobalt^8,49 to about one-half hour. The isotope dilution technique Is further utilized in that as many as three or four deposits could be prepared from the cobalt Isolated from a single sample.

Procedure. A sample containing about 10 mg. of co­ balt was weighed out and dissolved by adding HC1 and warm­

ing on a hot plate. About 30 ml. of concentrated acid per

gram sample was needed for the steels. The last remain­

ing residue was dissolved in HNO^ if necessary. Copper

alloys required HNO^ with a little HC1. Ten ml. of the

radioactive cobalt solution was added to the dissolved

sample and mixed well. Gases such as NOg were boiled off

46 47 and the solution filtered to remove silica. It was then evaporated to a syrup and the procedure below followed, according to the type of material being analyzed:

a. bteels and Ferrous Alloys

Most of the large excess of iron had to be removed prior to the addition of KNOg or basic ferric salts would have precipitated. The solution was made 6 to 8 N in HC1.

The volume was 100 - 175 ml.; it was then transferred to a

250-ml. separatory funnel, 75 ml. of ethyl ether was aaded,

and the flask was stoopered and shaken vigorously. Iron

was dissolved into the ether layer as ferric chloride.

The ether layer was removed and the extraction repeated.

Dissolved ether was boiled from the aqueous layer, the

solution again evaporated to a syrup and the following

procedure followed:

b. Non-Ferrous Alloys ( < 5 % Iron)

In order to eliminate remaining acids and chromium

and to reduce the volume afterwards, the solution from the

evaporation (or that from which iron was extracted) was

made basic with 30% NaOH. Most of the supernatant liquid

was discarded and the remaining slurry was po ired into two

or more 50-ml. Pyrex centrifuge tubes. After centrifuging,

the remainder of the supernatant liquid was discarded. The

precipitate was washed with water, a nd glacial acetic acid

was added to the precipitate until It just dissolved when

stirred. The solution was filtered through S & S black 4 8 line filter paper into a 400-ml. beaker. This removed some of the manganese as MnOg which formed in basic solution and did not redissolve in the acid. The solution was heated nearly to boiling and one-half its volume of hot 50# KHOg was added (fumesl). A precipitate of yellow potassium

cobaltinitrite formed shortly. After one-half hour the

solution was stirred, poured into two or more 50-ml. Pyrex

centrifuge tubes, and centrifuged. Most of the cobalt was

in the precipitate, so the supernatent liquid containing

nickel and the other constituents was discarded.

The precipitate was washed with 5% KNUg acidified

with a little acetic acid, then dissolved by warming with

1-2 ml. of 1:9 HgSO^. If the resulting solution was tur­

bid at this point, owing to silica, it was evaporated to

dryness in a 50-ml. beaker, the residue taken up in hot

dilute Ho S0. and the silica removed by centrifuging. If

the cobaltinitrite precipitate was not distinctly yellow

(a red-orown color indicated iron) or If the sample con­

tained manganese, a second precipitation was made.

The acidic solution was transferred to a 100-ml.

beaker and 20 ml. of buffer was added. Half normal NaOH

was added dropv^ise to pH 7.8 The volume was about 50 ml.

The solution was electrolyzed as described previously, the

specific activity was determined and the amount of cobalt

present In the original sample read from the standard curve. 49

Results. The results obtained for cobalt In four representative samples are shown In Table 11* As compared with the NBS values the results are good, especially for non-ferrous alloys. The relative standard deviation of a single measurement does not exceed 5%,

Separation of Cobalt from Iron

It has been reported that the precipitation of po­ tassium cobaltinitrite is satisfactory for the separation of cobalt from large amounts of iron,®0»51 3eVeral pre­ cipitations may be necessary and it was more rapid and con­ venient in the present work to perform at least one ether extraction of iron before the precipitation. Unless the weight of iron present In alloys Is at least ten times the weight of cobalt, it does not seriously Interfere and an ether extraction Is not necessary.

Conclusion

A satisfactory procedure for determining cobalt by

anodic deposition and the isotope dilution method has oeen devised. Incomplete deposition and non-adherence of depos­

its are no longer a source of error since the isotope dil­ ution method does not require that cobalt be Isolated quan­

titatively.

This method of determinatlon was verified by a prac­

tical application to alloy analysis In which the separation

of cobalt could be greatly simplified by taking advantage

of the isotope dilution technique. Table U

The .dialysis of hickel Alloys ana Steels . a A3o Canale Per Cc;nt Co Standard arror oj Value .,eiyht beix) sits round Jeviation I lean. A banple I it e rial ,> Co Graus e ./i -in* /i if*. lO^/O.n. 7iV. y Abs. Abs. jJD XOa- hi-Ou a.loy ^-.54 2.000 U 3 o 6 * 993 0.54 0*54 0.C12 0.00 06hi .;9 Cu 1417 7.053 0.54 • ^4j - -u 2.000 1373 7.233 0.5- 1445 6.920 C .53 2.000 14u5 0.325 0.53 J.129 0^ _ i.3S 157 Ci -ki-^n alloy C.I36 7.500 1422 7.033 0.14 0. L+ 0.005 0.004 72Cu lok.i 10An 1462 o.339 0.I4 0,02 2b 2.000 1315 7.605 0.15 1 1 0 1 7-219 _ 0.1 4. I. SB 126 a .ii i*x .steel 0. 3^ 3.000 1565 o.390 0.32 0.32 G.G11 0.O2 3 6,: ;.i 1603 6.220 0.31 0*4 ,.' 1 js 1553 6.420 0.33 3.000 1 ^ >9 0.320 0.32 1600 6.250 0.31

J -451 - - . 6*447 0,3?

I. Jo loi * * 1 — 0 37 liiaO^; C.-'i i 2.000 1630 5.953 0.45 0.47 l ». u 2 5 0.00 o4i*i l’/Cr 1510 1627 s. 143 0.47 1 ■>( : n --Ii 2.000 1540 ■j • 5ol \j *; ■ 16 j? 5.923 0*45 1675 5.970 0.45 . uOO 1530 6.536 0.50 1 5 U 6.439 0.49 ~ea .SILi 01 -o enaix V.

oCfl A STUDY OP THE

CATHODIC ELECTRODEPOSITION METHOD FOR COBALT

Because cobalt is often present after separations in a form unsuitable for weighing, e.g., the l-nltroso-2-naph- thol and ootassium cobaltinitrite precipitates, and since these are conveniently converted to a metallic electro- deposit, the most widely used gravimetric method for cobalt

is cathodic electrodeposition. Cobalt oxides, sulfate, pyrophosphate, or anthranilate may be used as final weigh­

ing forms also, but these require careful drying or Igni­ tion In addition to the usual operations of precipitation, filtration, and washing; hence, the simplicity of the

electrolytic method has maae it the foremost gravimetric

method.

Moderate or large amounts of cobalt (>0.25 grams)

may be accurately determined by any of several electro­

lytic procedures, but with smaller amounts, e.g., 100 mg.

quantities, there are certain complicating factors which

cause less accurate results. The most common difficulty

lies in the fact that special measures rust be taken to

deposit the last traces of coba]t from solution. Indeed,

It is so difficult to do this that most workers determine

the small amount of metal remaining in solution either

gravimetrically*^ or colorimetricallyOther factors

to be considered are: Inclusion in the deposits of foreign

material such as carbon, sulfur, or phosphorus; migration

51 5 2

of platinum from the anode to the cathode during electroly­

sis; and oxidation of the surface of deposits during elec­

trolysis and drying, A look at the long and detailed elec­

trolytic referee method for cobalt in iron and steel shows how tedious the exact determinations sre.^^

Several papers in the literature give methods for

the electrolytic determination of cobalt claimed to be

superior to previously described methods. The overall

objective of the present work was to examine, compare,

and to evaluate some of these methods, especially those

"standard methods" commonly used in routine analysis, as

to their use with cooalt samples weighing less than 100 mg.

No attempt was made to study all the factors mentioned

aoove by detailed procedures like the referee method.

However, the present study emphasized the most common

factor affecting results - removal of all the cobalt from

solution.

By using a radio-isotope of cooalt as tracer, it

was oosslble to obtain valuable information about an elec­

trolytic determination. In the first olsce, the activity

remaining in an electrolytic bath cfter deposition inoi-

cates the amount of cobalt not deposited under the con­

ditions of & given method; secondly, data showing the rate

of deposition indicate the minimum amount of time required

for deposition by a given method. Both measurements can

be made directly and conveniently by using a liquid counter. 53

Previous Work

Satisfactory results for the electroanalysis of co­ balt have been reported when deposition is made from either basic (ammoniacal) or from certain acidic solutions* The presence of various salts in the plating bath is said to be beneficial.

Some early investigators reported difficulty in pre­ venting the anodic deposition of cobaltic oxide during the

analysis.^6 A careful control of the cathodic potential during plating was one solution to this problem, out it was later realized that depolarizers such as hydroxylamine

or easily oxidizable organic substances prevent oxide formation.

Acidic electrolytes that may be used are those of

Smith^^ and Perkin.57,58 smith and coworkers obtained

excellent results when they plated coDslt from solutions

containing sodium formate or lactate plus a slight excess

of the carresoondinp acids. Unfortunately this work was

chiefly with large amounts of cobalt (usually 0.3 gram)

and not much attention urns paid to the amount of "residual

cobalt" or to small amounts of codeposited r.ateriai— factors

which become increasingly important as the amount of cooslt

is decreased.

Perkin and coworkers noticed that in the methods

commonly used, carbon or sulfur usually tend to be codeoos-

ited with cobalt, and they suggested a phosphate oath from 54 which bright metallic cobalt deposits may be obtained with little or no codeposition of phosphorus. Again the studies were made on relatively large cobalt samples (about 1 gram).

The chief disadvantage in using acidic plating baths is that the solution must be kept from becoming too acidic during deoosition or the plating will be slowed down or be stopped. On the other hand, they cannot be made too basic since cooalt salts may be precipitated, i.e., the hydroxide or phosphate.

Reproducibility in the preparation of plating baths is best when ammoniacal ammonium salt solutions are usea, and most routine work utilizes one of the following elec­ trolytes: ammoniacal solutions of ammonium acetate,^ formate,32 lactate^^ oxalatej?^ chloride,60 bifluoride,6-1- sulfate,62 bisulfite,thiocyanateand borate.in addition to one of these salts, a depolarizer is commonly used, e.g., glycerin^2 and salts of hydroxylamine6^ or hydrazine.^6 As mentioned previously these prevent anodic deposition or anodic reoxidation of cooalt and also aid in preventing anodic oxidation of the platinum electrode.

An excellent review of most of the early work on the electroanalysis of cobalt has been given by Watts.

The best recent publication on the subject is a paper by

Hague, Maczkowske and bright of the National Bureau of 54 St andards. 55

Experimental - Examination for Residual Cooalt

The conditions under which cobalt is electrodepos­ ited in some of the most frequently used electrolytic meth­ ods are shown in Table 12. Experiments were made in which each method was followed as closely as possible for the determination of 50 to 60 mg. samples. All residual elec­ trolyte solutions and wash solutions were checked for their cobalt content.

Procedure. Using standard active cobalt solutions

# 1 and 2 , solutions were prepared and the electrolyses were made as described In the method under investigation

(see Table 12). The cathode was removed, without inter­ rupting the current, by slowly lowering the beaker con­ taining the electrolyte and simultaneously washing the deposit with a spray of double distilled water. The entire contents of the beaker were then transferred to a 1 0 0 -ml. volumetric flask, diluted to the mark and mixed well. If the volume exceeded 100 ml., the sample wps either evap­ orated down or an aliquot was taken. These solutions were counted directly in the liquid counter apparatus described previously. The deposits were dried lor 5 minutes at 90° C.

and the weight was obtained by weighing the cathodes to the nearest 0.02 mg. before and after electrolysis. Deposits

can be easily stripped oy dipping in concentrated

A little hydrogen peroxide facilitated stripping by pre­

venting passivation, and cold nitric acid may be used. 56

Table 12

Conditions for the Electrodeposition of Cobalt

Exp’t Composition of Conditions , ** No • Electrolyt e* Amps ttime,volts References

1 2*5 g• NsgCQj 4, 30 nin., 6 Smith et al.32 4 ml. 94% HCOOH 95° C.

2 2.2 g. NagCOg 2-3,25 min.,8 ibid. 5 m l . conc. Lactic acid

3 20 ml. NH4 OH 2, 20 rcin., 7 ibid. 3.5 ml. 94% HCOOH

4 2 ml. 5# H3PO4 0.5-2 amps Perkin 25 ml. ln0& NaHgPO^ 30 min. et al.57'°b 0.1 g. NHp0H«H2S04 4.2-8 v. Taggart68 NH4 OH to pH 4

5 5 ml. 1:1 H2 S04 2 , 1 hr. Young62 NH^OH to neutral ana 40 ml. xs

6 25 ml. NH4OH 1.5,25 min.,6 Smith et al.^2 10 ml. 20% HOAc

15 ml. NH4OH 2-5 amps WagenmannbO 3 g. NH4 CI 45 min. Hague et al.54 0.1 g. NHgOH*HCl 4 v.

8 50 ml. NH4OH 4-7 amps Brophy65 5 g. NH4 CI 30 min. 0.4 g. NaH803

35 ml. NH4 0H 0 .5-0.8 amps Fine 61 20 g. (NH4 )2S04 1 hr. 2.5 g. NH4 HF2 4 v .

10 45 ml. NH40H 0.5, 1 hr., 4 Jilek and 0.5 g. NH2 *NHp 'HCl Vrestal66 2 ml. NHg-NHg-HgO

The volume of each solution was approximately 100 ml. initially. Current is in amps/dm.2 . Unless otherwise indicated, the initial temperature was 20-25°C. A 600 rpm rotating anode was used in each case. 57

For determining the residual cobalt, the same liquid counting procedure was used that was employed in standard­ izing the active cobalt solutions (page 177 ) . The observed activities were corrected for background and the amount of active cobalt calculated from the corrected count and the corresponding "solution specific activity" (page 177). Typ­ ical counting data are recorded in Appendix V. The "solut­ ion specific activity" of the standard active cobalt was checker each time samples were counted, and it was found to vary by no more than one per cent* This was sufficient to

give the desired accuracy without the usual efficiency cor­ rections. The small resolving time of the liquid counter

G-U tubes, 75 micro seconds, made it unnecessary to apply

coincidence corrections except when countc were quite large.

Neglecting the correction for a count of 3000/min. for ex­

ample, would introduce an error of only about 0 .5^. All

solutions were counted for five minutes each or for 1 0 , 0 0 0

counts, whichever time w s shorter. The activities of the

radio cobalt used were such that if a sample required the

full five minutes for counting, it contained less than

1 mg. of cobalt. Since most samples contained 1 mg. or

less the maximum absolute error that could be encountered

due to the statistics of counting w°.s VlQ ,000 x 100 or 10,660 1 »0% of 1 mg., 0.01 mg. This quantity is negligible com­

pared to the weight of the original samples, 50 mg. each. 58

Results. The results of the analyses obtained both with and without corrections for "residual cooalt," (i.e., cobalt left in the plating bath after the electrodeposition), are tabulated in Table 15. The "Diff." column -■lives the error In milligrams that results when one does not correct for residual cobalt. In the idial case these values should all be negative or zero and they should be equal in magni­ tude to the measured amounts of residual cobalt. The mean value for all the determinations (all methods) is 0.74 mg.

The last column to the right of the table, headed

"Sinn", lists the error when correction is made for residual

cobalt. With the exception of Expt. 4, deposition from

an acidic phosphate bath, these values are consistently

larger than those in the fourth column and the average for all determinations is 1.19 mg.

With one exception, the acidic phosohate oath, all result*? are seen to be positive even when corrections are

not made for residual cobalt and making the corrections

merely Increases the errors. For the phosphate oath rather

large amounts of cooalt remain undeposited; the positive

error after correction is relatively low in this case.

In some early work on the electroanalysis of co­

balt, 32,58 n0 mention was made of the corrections for re­

sidual metal. Good results were apparently obtained only

because of a compensation of errors. This oosslbliity

has been suggested by Brophy®^ in reference to some work 59

Table 13

Results of Cobalt Determinations by Several Methods Indicating the Amount of "Residual Cobalt" and the Errors

Exp11 Co Taken Weight of Diff a Residual Sum No. Mg. Deposits.Mg. Mg. Av. Co Av. Mg. Av.

1 59.8 59.7 -0.1 1.12 1.0 59.8 60.7 0.9 0.01 0.9 59.8 59.9 0.1 1.24 1.3 59.8 60.2 0.4 0.33 0.01 0.60 0.4 0.9

2 59.8 60.6 0.8 0.35 1.2 59.8 61.8 2.0 0.05 2.1 59.8 61.5 1.7 0.01 1.7 49.0 48.7 -0.3 1.10 0.68 0.28 0.4 1.6

3 59.8 61.3 1.5 0.01 1.5 59.8 61.0 1.2 0.07 1.3 59.8 60.6 0.8 0.06 0.9 49.0 50.0 1.0 1.13 0.07 0.05 1.1 1.2

4 59.8 59.6 -0.2 0.65 0.4 59.8 59.8 -3.0 4.03 1.0 49.0 47.9 -1.1 1.64 0.6 49.0 47.6 -1.4 1.66 2.00 0.3 0.6

5 59 .8 61.5 1.7 0.18 1.9 59.8 62.4 2.6 0.24 2.8 59.8 61.1 1.3 0.14 1.5 49.0 49.6 0.6 1.55 0.68 0.30 1.3 1.9

6 59.8 60.6 0.8 0.27 1.1 59.8 61.6 1.8 0.05 1.9 59.8 60.7 0.9 0.16 1. X 49.0 50.3 1.3 1.20 0.07 0.14 1.4 1.4

7 59.8 60.4 0.6 0.04 0.6 49.0 50.7 1.7 0.21 1.9 49.0 51.7 2.7 0.43 3.1 49.0 49.8 0.8 0.15 1.0 49.0 49.6 0.6 1.28 0.04 0.16 0.6 1.4

8 59.8 59.6 -0.2 1.31* 1.1 59.8 60.0 0.2 0.66 0.9 59.8 61.9 2.1 0.40 2.5 49.0 49.9 0.9 0.97 0.83 1.9 1.6 Cont'd next page 60 Table 13 cont'd

Results of Cobalt Determinations by Several Methods Indicating the Amount of "Residual Cobalt" and the Errors

Exp* t Co Taken Weight of Dlff . Residual Sum No. Mg. Deposits,Mg. Mg. Av. Co Av. Mg. Av.

9 59.8 59.1** 0.7 0.27 0.4 49.0 49.4 0.4 0.05 0.5 49.0 49.4 0.4 0.24 0.7 49.0 48.5 -0.5 0.25 1.40 0.49 0.9 0.6

10 59.8 61.9 2.1 0.02 2.1 59.8 50.0 1.5 0.05 1.6 49.0 50.0 1.0 0.04 1.0 49.0 50.0 1.0 0.17 1.1 49.0 50.0 1.0 0.02 1.0 49.0 49.9 0.5 1.28 0.02 0.05 0.5 1.3

* Experiment 8 values include some cobalt which was in a sulfur-sulfide layer that came off in the wash.

Experiment 9 values Include correction for platinum migration. The corrections were 0.1, 0.4, 0.2, and 0.0 mg. respectively. of Smith and coworkers.32 Data for Expt's 1 and 2 , Table

13, lend support to this explanation.

Measurement of the Rate of Deposition

Rate of deposition data were obtained by withdraw­ ing from the electrolysis vessel— during the electrodep­ osition— a small portion (about 10 ml.) of the electro­ lyte into a specially constructed tube which served as a

jacket for the small GM tube used In liquid counting.

The apparatus Is shown in Figure 3. The activity of the

small portion Indicated the coDalt remaining undeposited,

and consequently the per cent deposited, at the time of

the withdrawal. After the measurement, the small portion

was returned to the electrolysis vessel. i/Vhen a suitable

period of electrolysis had occurred another portion was

withdrawn, measured and returned* This process was re­

peated as desired during the course of the deposition.

The data from some preliminary experiments, Table 14, had

shown that the GM tube with the jacket tube gave linear

response during counting.

Because of a statistical error due to the limited

amount of time for counting, the values of per cent co­

balt deposited that were obtained in the rate study were

reliable to only about ±0.5%, Despite the error however

the study gives a good Dicture of the behavoir during pla

ting and gives another means of comparing methods. Used for the jElectStrodepo^1*^128 sition Rate Study

c 63

Table 14

Calibration of Apparatus used In Rate Studies

Active Co Taken Net Activity Activity/Mg.

Mg. Counts/Mln. (Showing Linearity)

1 78.0 78.0

5 380.2 76.0

10 756.7 75.7

15 1131.2 75.4

20 1527.6 76.4 64

After each rate study the cathodes were removed as usual with washing and the combined residual solution and washings retained for activity measurements of residual cobalt.

Results. The results of the rate studies are shown in Tables 15, 16, and 17. In Table 17 the time required for quantitative deposition is compared with the suggested time. In Exp’ts 1, 2, 4, 5, and 9 the suggested periods are considerably longer than necessary; however, the sug­ gested times were made for varying amounts of cobalt, us­ ually more than was used here, and the speed of rotaticn of the anodes used by previous workers may have been quite different from the 600 rpm apparatus used here.

The values of residual cobalt shown in Table 16 are

larger than would be expected from the values of per cent

cobalt deposited shown for the final measurement of each

rate study in Table 15. Small amounts of cobalt were

apparently lost from the deposits during removal and wash­

ing of the cathodes at the termination of electrolysis.

This is definitely a possibility In experiments one through

four where acidic electrolytes were used, and it is prob­

ably the reason for such large values of “residual cobalt”

as those reported In Table 13. The loss on washing the

deposits of experiment eight was due to removal of a thin

yellowish-green surface layer of sulfur and cobalt sulfide.

See also reference 69. 65

Table 15

Per Cent Cooalt Deposited vs. Time of Electrolysis

Ti] Experiment No. and Per Cent Deposited:

Ml] 1254 5 6789 10

0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

5 95.3 77.2 89.7 60.0 80.4 92.5 88.1 94.1 47.2 0.0

10 96.8 95.4 99.2 97.4 97.5 98.5 98.7 99.5 79.4 8.9

15 98.5100. 100. 99.8100. 99.7 99.7 99.3 94.4 38.5

20 100. - - 100. - 100. 99.9 99.5 97.8 60.0

25 ------99.5 99,8 99.3 81.1

50 ------99.6 99.8 99.8 91.4

45 ------100. - - 99.6

60 ------99.9 66

Table 16

Residual Cobalt In Solutions from the Rate Studies

£x p Tt No. Mg. Co ‘/to Co left In sol'n % Co Depc

1 0.09 0.18 99.8

2 0.06 0.12 99.9 01 o 3 0.21 • 99.6

4 0.61 1 .2 0 98.8

5 0.28 0.56 99.4

6 0 .36 0.72 99.3

7 0.10 0 . 2 0 99.8

3 0.28 0.56 99.4

9 0 .03 0.06 99.9

10 0.20 0 .40 99.6 67

Table 17

Time Required for Quantitative Deposition of Cobalt

Experiment No. Suggested Time* Actual Time**

1 30 min. 20 min.

2 25 15

5 20 15

4 30 20

5 1 hr. or less 15

6 25 20

7 45 45

8 30 25

9 1 hour 30

10 1 hour 1 hour

* References indicated in Table 12

Tabulated from Table 15 for comparison. 68

To further verify that losses of cobalt occur during the removal and washing of deposits, three deposits were prepared with a more active cobalt solution (#6 ). The plating bath used was that of Hague et al.®4 of the Nation­ al Bureau of Standards. After a deposition time of 45 min., twenty-five ml. portions of the residual electrolyte were removed with a pipet before the cathodes were removed or the current turned off. These portions were placed in

1 0 0 -ml. volumetric flasks, diluted to the mark and set aside for counting. This left 75 ml. of the residual electrolyte solution in the electrolysis vessel. The cathodes were then removed with washing in the usual way and the residual

solutions plus wash water were also retained for counting.

Prom the observed activities the cobalt losses were cal­ culated and are recorded in Table 18. It is apparent that the major loss is not due to cobalt which was never depos­

ited, but due to cobalt which redissolved when the deposits were washed. Lingane7^ has attributed similar findings for

lead and cadmium to losses resulting from air oxidation

during washing.

Explanation of Results

1. "Residual Cobalt." There are several reasons why

the last traces of cobalt are not removed easily* In the

first place, the strong tendency of cobalt to form com­

plexes and In particular the very stable Co^-^ complexes

could oossibly leave some metal in solution as negatively 69

Table 18

Cobalt losses during Washing of Deposits4*

Deposit Net Activity of Weight Net Activity Wt. No. a 25 ml. Portion, Cobalt 75 ml. plus Go Counts/Min. Mg. Wash, C./Min. Kg.

1 0.0 0 . 0 0 0 249.5 0.240

2 17.9 0.052 218.5 0.209

3 2.6 0.008 143.5 0.138

* The weights are expressed in terms of 100 ml. 70

charged Ions which would not be readily discharged cathod-

ically. In basic solutions, i.e., ammoniacal, these ions

could easily be formed as a result of air or anodic oxida­

tion. Secondly, there is the possibility of the anodic

oxidation of Co *1 to Co*** (ammonia complexes) followed oy

a resolution of deposited metal by the reaction of the

Co*** complex with the deposit. Diehl has mentioned this

as a possibility for cobalt.7** The reactions would be

something like the following:

at the anode:

Co (NH 3 ) 5H 2O 2 Co(NH3 )3H g0 e “

at the cathode:

SCodfH-jlgHgO*3 + 5NH3 Hg0 + Co 5Co(NH3 )5 Hgo t a

Cobalt losses during removal and washing of the

cathodes may be due to the following: (1 ) resolution of

the metal by acidic electrolytes, as in Exp'ts 1 through 4;

(2 ) a washing off of compounds of cooalt formed on the sur­

face of aeposits--particularly the sulfide as in Exp't 8 ;

(3 ) the explanation of Lingane7 0 which stated that resol­

ution is due to air oxidation during washing; (4) a re­

dissolving of cobalt by nitrites and other oxidation prod­

ucts of ammonia which are present in the residual electro­

lyte; a reaction such as the following might occur:

Co + 2N0£ ♦5NH3 + 3HgO Co( NH3 ) 5H 2 (/2+2N0 +40H7

” The process' was referred to as "Anodic Reoxidation". 71

The reaction la favored by the stability of cobalt com­ plexes; Hodgklnson and Bellairs*^ have discussed the ox­ idation of cobalt in ammonia solution.

2. Positive Errors. There have been numerous re­ ports of positive errors in the electroanalysis of cobalt and the same is true for n i c k e l . ^ 3 Codeposition of for­ eign material is generally held responsible for these, although in analyses in which careful determinations of foreign matter were made, the corrections thus obtained did not completely explain the results.^ It is probable that contaminants such as oxide, hydroxide or water have not been tested for carefully.

A statement by Young®^ that the electrolysis should not be prolonged after depositing "all the cobalt" or

"results will be high^' along with the observation of

Nicol74 that deposition from very dilute solution gives oxides and hydroxy compounds, leads one to believe that this may be the explanation for both positive results and residual cobalt. Nicol states that solutions of concen­ tration less than 0.005 N In cobalt ( fca 15 mg./lOO ml.) are subject to detectable oxide and hydroxide formation.

His work dealt with water solutions of cobalt salts and not ammoniacal solutions, ^iicol prepared several basic cooalt salts by ordinary chemical methods and obtained the thermogravimetric ignition curves for them. The com­ pound he prepared which gave an Ignition curve most sim- 7 8 imilar to that of the electrodeposited cobalt compounds

corresponded to CoSO,^-3Co(0H)g *HgO. The electrolytlcally prepared compound was more soluble in water and salt sol­ utions than the corresponding basic 3alt.

If the process responsible for forming these oxides

and hydroxides Is assumed to take place during electro­

lytic analyses, a determination would proceed as follows:

Metallic cobalt would be deposited normally until the cobalt

concentration in the plating bath dropped to 0.005 N. At

this point a reaction or series of reactions would begin

to take place wnieh is responsible for deposition of the

C0 SO4 *3Co (0H)g*HgO and/or relatec compounds. Y/hen the

cathode Is removed from the electrolysis vessel at the

end of deposition, part of the cobalt "surface compounds"

are washed off or redissolved by the wash water, but enough

remains on the deposit to give positive errors.

The absolute errors due to such a orocess would 00

essentially Independent of the amount of cobalt being de-

oosited when aoove 0.005 N initially, but would depend

mainly on the surface area of deposits. With a sufficiently

large sample the error would not be noticeable, i.e., it

would be negligible, and this seems to be true when heavy

cobalt deposits are used.^ This reaction and washing of

deposits following it are usually not reproducible and con­

sequently there is a relatively large variation In the pos­

itive errors reported. In fact, any surface phenomena 73 which, might cause positive errors and cobalt losses would not be likely to be reoroduclble.

Incidentally, cadmium has been observed to exhibit some striking similarities to cobalt with regard to pos­ itive errors and the difficulty of depositing the last traces of metal.7^- It Is Interesting to note that NIcol made similar observations concerning oxide and hydroxide formation In electrolysis of cadmium.

The formation of surface compounds, given above as a possible source of error and as being partly responsible for residual cobalt, is to be distinguished from the occlu­ sion of foreign material to which reference Is generally made. As mentioned previously, carbon, sulfur and phos­ phorus are often occluded in the elementary form, the en- trainment occurring continuously throughout the duration of electrolysis. That is, the more metal deposited, the more foreign matter present. Shakhkeldian and Nasova®® have assumed this to oe true in the compensation method

given for errors due to csroon in heavy cobalt deposits made from oxalate solutions.

A Test for the Formation of Surface Compounds

If the hypothesis for the explanation of positive

results and cobalt losses based on NIcol's observations

is correct, one would expect to find that deposits obtained

when only oart of the cobalt is plted would be more nearly

pure metallic cobalt, and that the error would become larger 74 as the last few mg. were deposited.

Experiments were made in which the depositions were purposely stopoed before electrolysis was complete. The amount of metal remaining undeposited was determined in the usual way with the liquid counter. Deposits were re­ moved, washed, dried and weighed as before. The results are shown in Table 19.

If the deposits that weigh 35 mg. or less had con­ tained little or no foreign matter, then the sum of that value and the cobalt remaining In solution would have been equal to the amount of cobalt taken, and the possible ex­ planation given above would appear to be the correct one.

The "Error” column figures are, however, still all pos­ itive and not significantly smaller than those obtained when complete deposition is made. Hence, it must be con­ cluded that the explanation was not correct, at least inso­ far as the assumption of the concentration at which surface compounds form. 75

Table 19

A Test for Formation of Surface Compounds

Exp* t Co Taken Wt. Deposits Co Remaining Sum "Error1 No . Mg. Mg. in Sol'n, Mg. Mg. Mg.

1 49.60 50.40 0.09 50.49 0.89

2 ti 50.79 0.08 50.87 1.27

3 ii 35.75 14.35 50.10 0.50

4 n 41.00 9.64 50.64 1.04

5 it 38.88 10.95 49.83 0.23

6 ii 40.45 10.28 50.73 1.13

7 it 30.36 20.65 51.01 1.41

6 it 46.37 4 .88 51.25 1.68 76

Determination of Residual Cobalt

In an electrolytic determination It is important to know when the sample has been quantitatively deposited.

The disappearance of the color due to cobaltous Ion or the ammonia complex is not sufficiently sensitive for this pur­ pose. A small portion of the electrolyte Is generally re­ moved and tested. Young^ gave directions for the use of

ammonium sulfide, potassium thiocarbonate, phenylthiohydan- tolc acid and nitroso-R-salt for these tests. Recently

Maletskos and Irvine*^ gave a thiocyanate-amyl alcohol extraction method for the detection.

Of these reagents, the hydantoic acid Is not readily

available. Nitroso-R-salt Is by far the most sensitive and

suitable for spot plate tests. In the present work, not

only was the R-salt suitable for qualitatively following

the completeness of deposition, but It could also be used

for raoid estimations of the amount of residual cobalt

left In the plating bath and washings. The following pro­

cedure was successful:

Using standard cobalt solutions containing 0.2, 0.4,

0 .6 , 0 .8 , and 1.0 mg. of metal perl 100 n l ., a series of

color spots was developed on a porcelain spot plate. In

each test 5 drops of standard solution, 3 drops of saturated

sodium acetate, 1 drop of 0,5% reagent, 1 drop of 2N HNO^,

and 2 drops of water were used. 7 7

The residual electrolyte solutions (including wash) were diluted to 100 ml* and mixed. Using these solutions color spots were developed in the same manner as with the standards. A visual comparison of the spot with those of the standards gave a good approximation of the amount of cobalt present. Reducing agents such as sulfite, hydrazine

salts, etc., had to be destroyed before the test by heating with a little nitric acid.

The data of Table 20 show results for some typical cnees. This procedure was not satisfactory for amounts of cobalt less than 0.2 mg./lOO ml.; in such cases a larger

amount of solution could be used.

With ammonium sulfide or potassium thiocarbonate as

reagents bo detect residual cobalt, negative results were

obtained in every case where less than about three mg. of

cobalt was present. 78

Table 20

Use of Spot Plate for Determining Cobalt in Electrolytes

Cobalt Pound in Typical Cases

By Activity By NRS S] Mg. Mg

1.12 1.0

0.00 0.0

1.24 1.0

0.35 0.4

0.05 0.1

0.01 0.0

0.33 0.2

O .06 0.0

0.64 0.6 79

Summary

1. A study was mad© of the quantity of cobalt left

In the electrolytic solution after electrodeposition for ten of the generally used electrolytic procedures for co­

balt. It was shown that some cobalt remains in solution

in every case. The amount varied from 0.01 to 4.0 mg. with an average for 43 determinations of 0.52 mg. The

only distinction that can be made between electrolytes,

as to the amount of metal remaining in solution, is that

neutral or slightly acidic electrolytes usually tend to

retain more metal, although for these electrolytes the

results are not consistent.

2. It was shown that "residual cobalt" is usually

due to cobalt left in solution as a result of the washing

of deposits and not simply metal which was never depos­

ited. Cobalt resembles lead, cadmium and tin in this re­

spect

on the particular metal and is less the smoother the de­

posit ,76

3. Electroanalytical data for cooalt, Table 13,

consistently show positive errors not completely account­

able for by corrections for sulfur or cnrbon.^ The av­

erage for 43 single determinations was 0.74 mg. before,

and 1.19 mg. after correcting for residual coDalt. This

represents errors of 1.38 and 2.12% respectively. Correc­

ting data for residual cobalt Increases the errors. The 80 good results given by some previous workers who did not correct for residual cobalt or for foreign matter may have been due to a cancellation of errors.

4. Although some metal may remain in solution as a

Co1 ^ 1 complex that is not easily deposited, most of the losses are probably due to an oxidation of deposits. The deposit reacts with Co^^, with air, or with decomposition products of ammonia. The formation, during the last oart of electrolysis, of cobalt compounds (oxides, hydroxides, basic salts and hydrates etc.) on the surface of deposits appears not to be the exolanation for cobalt losses and oositive results.

5. It was shown that a quick spot-plate method of estimating residual cobalt after removal and washing of the cathode, based on the use of nitroso-K-salt, is satis­ factory for most routine work. THE PRECIPITATION OP COBALT AS COBALTINITRITE

The precipitation of cobalt as yellow potassium cobaltinitrite was reported more than 100 years ago by

N. W. Fischer7 7 and by Saint-Evre.7® This reaction has been used principally for the separation of cobalt from nickel. Its applications have varied from special cases such as the preparation of nickel-free cobalt for atomic weight studies,79 to its use in routine analysis for co- oalt in ores,8^ in steels,88 or In special alloys.88

Many modifications or variations of Fischer's orig­ inal method have appeared. Most standard texts^®*49 #£11 give a procedure very similar to Brunck's modification.8^

More recently, Kallmann8 8 gave some important observations concerning the Interference difficulties usually encount­

ered and suggested modifications which resulted In a con­

siderably Imoroved method. In a very comprehensive study,

Cumbers and C o p p o c k 8 ^ concluded that the precipitation of the dipotassium sodium salt has distinct advantages over

that of the potassium salt in cobalt determinations.

In addition to the numerous volumetric or gravimet­

ric determinations of cobalt that are based on the for­

mation of cobaltinitrites, there are many direct or indi­

rect methods for ootassium which depend on the formation

of potassium cobaltinitrite,84 dipotassium sodium cobalti-

nitrite,^9,65 or the double cobaltinitrites of potassium

with lead and silver.8 8 »87 Thallium Is the only other

01 82 metal which has been successfully determined as a cobalti- nitrite.®8 Several other cobaltinitrites, including those of lead and of several amines, e.g., p-bromoaniline, were reported by Cunningham and Perkin,®® but because of their high solubility or the difficulty in preparation very few analytical applications are possible for these or for the large number of similar comnounds prepared and studied by

Ferrai and coworkers.®0 Burgess and Kainm®^- reported a var­ iety of cobaltinitrites which are of value for quantita­ tive work, for example, the mercurous compound, lead and silver double salts with several other metals, etc.

The use of the cobaltinitrite reaction as a qualita­ tive test for cobalt has been described by Benedict, by Yagoda and Partridge,who precipitated the cesium salt, and by Duval and Soye.94

The Reaction

Acetic acid-acetate is used as a buffer to maintain a slight acidity during the reaction. Cooalt is first oxidized to the 3 state, then precipitated:

Co + i3+2H++ NOg Co+3-V NO + HgO

Co+5 + 6N02" Co(N0g )6 "3

3K+ + G o ( N 0 2 )6"3 ^ K3 Co(N0 g )6

The product is best represented as K^CotNOgJg'xHgO,

since the amount of water may vary from 0 to 4 molecules

depending on the conditions of formation,98 and particu­ 83 larly the time of standing. It is said to be lattice water rather than water of hydration.®®

In the presence of sodium ions the precipitate is a mixture of varying amounts of the sodium-potassium and the potassium salts, i.e., K^NaCoCNC^e and K3 Co(N0g)g. The former is one of the compounds usually precipitated in ootassium determinations. Both compounds are yellow.

Although some mention will be made of the sodium- potassium double salt, the oresentwork is concerned chiefly with the potassium salt as precipitated in cooalt determin­ ations .

Interfering Elements

Kallmann's study8® has clarified the Interference problem to a large extent. Prior to his work most authors mentioned the Interference of certain substances such as oxidizing agents, free mineral acids, large quantities of iron, chromium and aluminum, the alkaline earth metals, etc.,®2 but they said very little about the exact nature of the interference, or how It could be prevented. They

apparently assumed that the interference difficulties were insurmountable and that the separation is not generally

applicable. Kallmann, however, gave a comprehensive dis­

cussion of the nature of the interference and gave prac­ tical suggestions for improving the method.

Oxidizing agents and free mineral acids interfere

Decause they decompose the reagent: 84 H+ + N 0 2" ^ HNOgj 2HN0g HgO 4* NO + NOg"

2Mn04“ +5N02" ♦ 6H* ^ 2Mn^ + 5N03" + 3H 2°

Alkaline earth metals interfere in cobalt-nlckel separa­ tions by causing some nickel to be carried down as a ni­ trite,97 e.g., K2CaNl(N02 )6 .98

Aluminum, ferric iron, and chromium are partly hy­ drolysed when the potassium nitrite is added. Ferrous and manganous ions are oxidized first, then hydrolyzed:

N02“ + HgO *=* HNOg *»■ OH"

H20 + Fe+ 2 + N02" ^ Fe*3 +- NO + 20H"

F e +3 + 30H" ^ Fe(0H)5, or Cr(0H)3, etc.

When potassium nitrite is added to a slightly acidic sol­ ution of cooalt and other metals, the pH of the solution

Is brought up to about five where it is held by buffer action of the acetic acid-acetate. Hence, all ions that

Drecipitate as hydroxides at a pH of 5 or lower are hydro­ lyzed, e.g., Al+3, UIV, Th, Sn*1 , Fe***3, ana Z r .99

Kallmann's very effective solution to this problem was to comnlex the hydrolyzable Ions with tartrate or fluoride and mask them. He obtained successful separations of cooalt from mixtures containing tin, iron, zirconium, thorium, aluminum, chromium, zinc, cooper, manganese, nickel, antimony, arsenic, and bismuth.

The Rate of Precipitation of Potassium Cobaltlnitrlte

The rate of precipitation has received very little attention by previous workers. When Indicating the amount 85 of time required for quantitative precipitation, each, writer aeems to have quoted a previous worker. The usual statements found are "•. not less than 12 hours of stand­ in g .."^0 0 or "..allow it to stand 24 hours"31, "..allow to stand in a warm place at least 6 hours preferably over­ night .. "Allow to stand cold, at least for 4 hours, pre­ ferably overnight.11

Other references to rate simply indicate observed trends and do not give very useful data. Mellor^ states

that "with dilute solution, the precipitation occurs only

after the mixture has stood for some time." This indicates

that for a given amount of cobalt, volume is an important

consideration when cobalt is to be determined. Kallmann^O

in the work mentioned previously, said, "Smaller amounts

( < 50 mg. of cobalt) usually come down in a very short

time." Though these statements may seem contradictory,

it should be remembered that each refers to a iven pro­

cedure for the determination.

The need for a comprehensive study of the rate of

precipitation of cobalt by ootassium nitrite is obvious.

Periods of 4, 6 , 12, and 24 hours or "overnight" have all

been suggested as the correct amount of time required for

quantitative results in certain cases, but generally one

can hardly be certain of the minimum amount of time re­

quired . 86

In addition to giving data useful for determinations of cobalt and potassium, a Dhysico-chemical study of the cobaltinitrite method should also be of interest to those who are concerned with determinations based on the precip­ itation of analogous compounds, e.g., bismuth or sodium determinations by Cs2NaBi(N0 2 )6 * a*1** potassium or cal­ cium estimations in which I^CaNitNOgJg is precipitated.

Measurement of Rates

This work involved measurement of the extent of precipitation with time as certain factors were varied.

The factors of greatest importance that were considered were: (a) volume, (b) temperature, (c) the amount of cobalt, (d) the excess of potassium nitrite, (e) acidity, and (f) the presence of other material that may be present during separations.

The effect of time of standing on the amount of cobalt precipitated was noted as each factor was varied, the other factors being held constant. The use of radio-

cobalt tracer facilitated this otudy greatly since the

amount of cooalt that remained unorecipitated at a given time could be measured by simoly noting the activity of

a portion of the supernatant liquid.

At a given time after the addition of the reagent,

approximately 15 to 30 ml. of supernatant liquid was fil­ tered off and a 10 or 25 ml. portion was taken for activ­

ity measurements. By comparing the activity of this oor- 87 tion with the total activity added and by using the known total volume of the reaction mixture, the per cent cobalt remaining in solution, and hence that precipitated, was calculated:

% ppt'd at time t _ 100 - yf** ^ x 100 ™ ” initial activity/ml. % = 100 Ji - A^rjj where A- is the activity of v ml. (usually 10 or 25 ml.) of the filtered reaction mixture.

A0 is the total activity added, calculated from the "solution specific activity" of the cobalt used and the weight of cooalt taken.

V is the initial total volume of the reaction mixture.

The liquid counter apparatus shown in Fig. 11, oage 175, was used in all activity measurements.

Procedures

The procedures given below were followed carefully,

one factor at a time was varied, and the time was noted at

which precipitation was initiated. After standing for

periods of |, 1, 2, 4, 8 , 16, and 24 hours, some super­

natant liquid from one of the samples was filtered off

using Sealas microporous filter crucibles and suction

filtration. Immediately a 10, 25, or 50 ml. portion of

the filtrate was pipetted into a 100-mi. volumetric flask.

The reaction was stopped Dy adding to the fUask a few ml.

of strongly acidic (HN03 ) sodium dichromate or potassium

permanganate to destroy the reagent (fui.esi). The beaker

containing precipitate and the remainder of the superna­ 88 tant liquid was retained for further measurements* Two, three or more measurements could be obtained from each samole, depending on the volume. After diluting the vol­ umetric flasks to the mark with water, the solutions were mixed and counted.

a. The Standard Procedure*®

Potassium carbonate was added to an acidic solution of radioactive cobalt (25 mg. of cobalt in 25 ml.) until it was neutral to litmus, then 2-3 ml. of glacial acetic acid was added and the solution was heated to boiling. A boil­ ing solution of 15-20 grams of potassium nitrite and 2 ml. of glacial acetic acid in a total volume of 25 ml. was then added. The mixture was kept hot for one-half hour, then allowec to stand in "a warm place”; this was taken to mean about 40° C.

b. Kallmann’s Modification^

The acidic solution containing the radioactive co­

oalt was pi iced in a 400-rol. beaker and evaporated under

a heat lamp to dryness. After cooling. 5 grams of tartar­

ic acid were added and the solids were taken up in 75 ml.

of water by warming on a hot plate. If oxides resulted

from the evaporation they were redissolved by adding a

few droos of nitric acid along with the tartaric. A sat­

urated ootassium hydroxide solution was aaded dropwise

until the solution became alkaline to litmus. Potassium

hydrogen tartrate orecipitated during this acdition and 89 redlssolved just as the solution became alkaline. This was expected in view of the relative solubilities of tar­ taric acid, the acid salt, and the potassium salt, which are 120, 0.42, and 150 grams per 100 ml.10** Glacial acetic acid was then added until the solution was neutral; then a

4 ml. excess was added. Precipitation was made by heating to near boiling and adding 200 ml. of hot potassium ni­ trite solution (100 grams dissolved in hot water plus a few drops of glacial acetic acid). The beakers were then covered with watch glasses and held near boiling for 5-10 minutes or until fumes ceased. The total volume was noted and the solution was allowed to stand cold. Because of the fumes these operations were performed in a hood. The watch glasses heloed reduce evaporation.

Results and Discussion

The Effect of Volume. The effect of volume on the rate of precipitation of cobalt is indicated in Table 21.

In agreement with Mellor,1 the rate decreases with increas­ ing volume of the reaction mixture, I.e., it decreases with decreasing cobalt concentration when the other factors remain constant. when the volume was increased above 200 ml, the time of standing for quantitative precipitation increased to 24 hours or more, indicating that during analyses the volumes should be kept as small as is con­ veniently possible. 90

Table 21

The Effect of Time on Cobalt Precipitation under Various Conditions

Per Cent Cobalt Precipitated:

Volume varied, 25 mg# Co, 20 grams KHOg, standard procedure

Total Time in Hours Volume 0.5 1 2 4 8 16 20 24 48 Ml.

50 99.9 100.0 100.0 -

100 100.0 100.0 -

200 99.9 100.0 99.9 100.0 -

285 77.4 92.1 98.6 91.3 95.6 99.5 99.8 71.4 87 .6 96.5 98.5 99.4 99.5 - 99.8

250 71.4 83.5 91.9 97.2 97.8 98 . 6 _ 98.8 57 .0 69.6 84.4 92.3 94.9 - 96.5 — 98.6

300 12.4 33.5 57.5 69.0 77.8 80.4 80.0 86 . 6 — 20 .5 44 .4 65.3 71.2 78.6 79.6 79.9 85 .2 91

The rate of precipitation is quite sensitive to difficultly controlled factors such as the rate of decom­ position of nitrous acid, cobaltinitrite ion, and ions containing Co111. These are greatly affected by the amount of stirring, the vigor of boiling of the reagent and the mixture, etc. Nevertheless, by adhering to a fixed pro­ cedure for handling each samole, the course of the reaction was followed fairly well. In successive experiments under the same conditions the values could be reproduced to ■£ 5JKI.

The Effect of Temperature. Table 22 and Pig. 4 show the results of a study in which the effect of temperature on precipitation was noted. A reaction mixture volume of

300 ml. was used here since rates are easily measured at these low concentrations. The reagent and cobalt solutions were Drought to the desired temperature-, then mixed and the container Disced in a constant temperature water bath at the same temperature. This procedure differs from the stan­ dard method, in which the reagent is always added at the boiling temperature, and then allowed to cool* As in all these rate studies, samples of supernatant liquid were removed periodically, filtered nnd a portion pipetted out for activity measurements.

Results for the four samples run at different temp­ eratures varied widely. Precipitation was quantitative in b hours for the 20° C. sample, the first signs of ore- clpitation having appeared about two minutes after mixing. Table 22

The Effect of Time on Cobalt Precipitation under Various Conditions

Per Cent Cobalt Precipitated:

Temperature varied, 25 mg . Co, 20 grains KN0 g , vol . 30<

Temp • Timein Hours °C. 1 2 4 8 18 24 48

20 82.3 94 .4 99.1 99 .6 79.6 92.6 99.0 1 0 0 . 0 -

35 37.9 60.2 82.6 91.1 96.5 96.7 - 47.2 67.6 86.9 92.9 96.3 96.4 -

50 50.5 65.1 75.6 73 .9 83.2 83.2 82.3 42.8 59.2 67.9 75.8 78.3 78.6 80.5

Boiling 0.0 no oot formed 0.0 n ti it Per Cent Cobalt Precipitated 100 20 60 40 80 T h eE f f e c to fTi m eo nt h eP r e c i p i t a t i o no fC o b a l t O 20 °C . A A □ 35°C. O20°C. X Standardprocedure ( N op r e c i p i t a t i o na t aPo s t a s s i uCo m b a l t i n i t r i t e . T e m p e r a t u rVa e r i e d T i mi e nHo u r s Pig. 4 50°C. I00°C)

20

24 93 At 35° C. precipitation was 96# complete in 24 hours, while for the 50° C. samples the value was about 80% for the same

period of time. This trend is continuous up to the boil­

ing temperature, at which these dilute cobalt solutions

gave no precipitation with the specified amount of reagent.

A precipitate did form however, when the boiling mixture

was cooled*

It was first thought that this phenomena was caused

by decomposition of most of the potassium nitrite, and a

series of titrations of nitrite with permanganate was done.

The titrations showed that most of the reagent remains

even after boiling treatments, as is shown in Figure 5.

A better explanation is found in the paper by

Burgess and Kamm,®^ where it is stated that heat affect3

a decomposition of cobaltinitrite ion by removing Co

through its reaction with nitrite:

Co(NO* )fc Co+5+■ 6N0g"

Co4-3 4- N02" NOg + Co4-2

The same reactions explain why satisfactory solubility

data for cobaltinitrites are not available; a reversible

equilibrium is not established.

Hence, a short period of heating to slow down pre­

cipitation, to lessen coprecioitation, ana to give a more

granular and easily filtered precipitate, followed oy

cooling to precipitate the remainder of the cobalt, would Amount of Potassium Nitrite Present, Grams 20 8 - h Dcmoiin f oasu Ntie ih Time with Nitrite Potassium of Decomposition The ie n Hours in Time Fig.5 20 95 96 seem to be the optimum procedure. The standard procedure^® gives such directions but some authors do not suggest heat­ ing at all.49

The Effect of the Cobalt Concentration. The per cent cobalt precipitated by a given amount of reagent decreased as the amount of metal was increased, although with the amount of reagent used in these studies the influence on rate was only slight until quite large cobalt samples were used. See Table 23. The "overnight" period was necessary when a 1.5 gram sample was used, but one seldom works with large amounts, due to the large amount of precipitate in­ volved. For samples of 1 gram or less, a one hour period

is sufficient if the volume can be kept down to 100 ml.

The Effect of the Potassium Nitrite Concentration.

V«hen successively smaller quantities of reagent were used, a point was soon reached at which the rate decreased. The

deta showing this. Table 24, are somewhat similar to that of

Table 21, the volume study, if compared with respect to the

potassium nitrite concentration. For example, 5 grams of

reagent in 50 ml. orecipitated the cobalt quantitatively

in 2 hours, while 20 grams in 200 ml. required 1 hour. The

difference, though not very significant, is possibly due to

a varying extent of decomposition of reagent.

The color of the precipitates was of interest in

this study. When cobalt was in excess and precipitation

was only partial, the product was deeper yellow in color 97

Table 23

The Effect of Time on Cobalt Precipitation under Various Conditions

Per Cent Cobalt Precipitated:

Amount of Co varied, 20 grams KNO2 , 100 ml.

Wt. Co Time in Hours Grams 0.5 1 2 4 8 12

0.025 100.0 100.0

0.125 100.0 100.0

0.525 100.0 100.0

1.025 97.4 99.8 99.9

1.525 94.0 97.2 97.2 99.2 99.9 98

Table 24

The Effect of Time on Cobalt Precipitation under Various Conditions

Per Cent Cobalt Precipitated:

Amount of KNOg varied, 25 mg. Co, 50 ml. vo luma

Grams Time in Hours KKOg 0.5 1 2 4 8 12 48 20.0 100.0 100.0 —

15.0 100.0 - 100.0

10.0 100.0 99.9 100.0

5.0'" 99 .0 99.6 99.8 100.0 -

4 .0*# 47.3 50.4 50.2 44.6 58.0 - 58.8

3.0** 10.7 17.3 14.3 15.7

# Each sample was used for 2 measurements.

# The precipitates were orange colored as compared to yellow

when the reagent was in large excess. 99 than when the reagent was In excess. Sadtler9^ stated that observed color differences are due to a variation in the amount of water of hydration contained by the product.

The Effect of Acidity. Acidity is important only with regard to the amount of reagent decomposed by acid.

In every precipitation there is a leveling effect produced by hydrolysis of the potassium nitrite. The final oH of the solution from which orecipitation is made always falls between 4.5 and 5. To promote buffer action and to insure that no cobalt hydroxide forms during precipitation, acetic

acid is always used to assure a slight initial acidity.

In the standard procedure a little potassium car­ bonate is used to neutralize the acidic cobalt samoles

prior to the acetic acid addition. It should be noted

that if more than enough of the carbonate is added, there

is a tendency to precipitate or to form a colloidal suspen­

sion of cobalt and other metal hydroxides which are not

immediately redissolved when acetic acid solution Is adued

and hence the cobaltinitrite precipitate will contain an

amount of hydrated oxides. It has been reported that the

cobaltinitrlte always contains a little hydreted cobaltic

oxide.Tnis material may also affect the rate of pre­

cipitation of the cobaltinitrlte, although no marked efiect

was noted in the present work.

The Presence of Other Materials. Large am.ounts of

nickel, copper, sine, and cadmium had no effect on the 100 rate of precipitation of cobalt in either the standard method or Kallmann's modification. See Tables 25 and 26.

Similarly, large amounts of tartrate, fluoride, chloride, and sodium Ions did not appreciably reduce the rate.

Studies of Kallmann's Method. Two studies were made.

The first was mentioned In the above paragraph and showed that metals which require tartrate masking do not notice­ ably influence the rate of cobalt precipitation. The other study, Table 27, showed that precipitation is complete in a shorter period of time for small amounts (less than 0.3 g.) than for larger amounts of cobalt (0.5 and 1 gram).

Other Studies of Cobalt Precipitation

The Precipitation of Potassium Sodium Cobaltinitrlte.

Cumbers and Coppock®^ stated that the precipitation of

KgNaCo(N0 2 )Q proceeds at a more rapid rate than that of the tripotassium salt. However, they did not make any

rate measurements, but aooarently accepted the word of previous workers in this respect

To show whether the triple salt is actually pre­

cipitated more rapidly, it was decided to precipitate co-

oalt in each form, duolicating as nearly as possiDle the con­

ditions of precipitation of the two compounds, and to com-

onre the measured rates.

procedure. In each precipitation 25 mg. of cooalt

was used. The standard procedure outlined previously was

followed except that in one case potassium nitrite was 101

Table 25

The Effect of Time on Cobalt Precipitation under Various Conditions

Per Cent Cobalt Precipitated:

The Presence of Other Materials.

Volume 100 ml., 25 mg. Co, 20 grams iiMOg

Materials Time in Hours Present 0.5 1 2 4

0.5 g. ea. of 99.9 99.9 Ni, Cu, Zn, Cd*

2.5 g. Ni* 100.0

5.0 g. H2C4 H4 O 6 100.0

5.0 grams NaP 99 99.4 .4 99.8 99.9

25 g. NaCl 100.0

Ni, Cu, Zn, and Cd were added as the sulfates or nitrates. Table 26

Par Cent Cobalt Precipitated vs. Tima. The Effect of Other Metals

Kallmann's Method— 0.5 g. Co Each Study

Other Metals Present* Grains Hours: 0.5 1 2 4 8

Cu 0.5, Sn 0.1 - 99.92 99.99

As Ac Bi 0.1 ea.

NI 0.15, Sb 0.05

Cu 0.5, Cd Ac Zn0.15 - 99.98 100.0

NI 0.05

Ba 0.1, Ca 0.05

Cu 0.25, Ca 0.25 - 99.97 100.0

Ba 0.1, Pb 0.1

As Ac Fe 0.1 ea.

NI Ar. Mg 0.05 ea.

A1 Ac Cr 0.2 ea. - 99.93 99.97

Mn 5c Ni 0.1 ea.

Zr 0.3, Th 0.05

Mg 0.05

These metals were added as dissolved oxides, nitrates

or sulfates. The alkaline earths were easily removed

as sulfates, as stated by Kallmann. 103

Tabla 27

Per Cent Cobalt Precipitated vs. Time. Amount of Cobalt Varied

Kallmann's Method-- 100 g. KNOg and 300 Ml. Volume

Grams Co Time said Per Cent Precipitated: T* f i I f AT I Hours: 0.5 1 2 4 24

0.025 99.99 100.0

0.100 100.0

0.300 100.0

0.500 99.97 99.96

0.750 98.82 99.34 99.86 99.95 100.0

1.000 98.52 99.49 99.88 99.97 99.93 104 used while in the other a mixture of potassium and sodium nitrites was used. For the latter the molar ratio of

Na/K was £5/1 as suggested by Cumbers and Coppock. Twenty grams of 87% potassium nitrite is equivalent to 0.205 moles of this compound. A mixture of potassium and s d - dium nitrites in which the Na/K ratio is £5/1 contains

0.205 moles in 15 grams. These are the quantities of reagents used in the two precipitations.

Results. When an equal number of moles of reagents was used, a much larger per cent of cobalt was precipitated

by the potassium nitrite. Even when equal weights of the reagents were used--20 grams each— the potassium nitrite precipitated more cobalt in 24 hours, i.e., 80% compared to 55% for the K-Na reagent. These data are shown in

Table 28. Increasing the amount of either reagent will

precipitate larger amounts of cobalt, e.g., 30 grams of

the mixed reagent brought down 99% of the cobalt in 24 hours.

A probable exolanation for the statements found in

the literature that the potasslum-sodium salt is precipita­

ted. rnore rapidly lies in the fact that until recent years

commercially available potassium nitrite was inferior in

ourity to the corresponding sodium salt. This possibility

was suggested by De Konlck^-O® ±n 1903. 105

Table 28

A Comparison of KNOg and KN0g+ N a N 0 g

as Reagents for Cobalt

The Effect of Time on Cobalt Precipitation.

Amount of Cobalt, 25 mg. Volume 300 ml.

Reagents used Time in Hours and Per Cent Precipitated

1 2 4 8 12 24 48

KNOg, 20 g.* 16.1 39.0 61.4 70.1 - 80.0

KN02+ NaNOg

15 g. 0.0 0.0 - 2.0 - 9.7

20 g. - 8.2 24.3 - 54.8 88.4

30 g. 73.8 86.0 94.4 - 96.9 99.4 99.6

■k- These data are average values of that in Table 21 106

The Effect of Organic Liquids. It has been reported that alcohol Increases the sensitivity of qualitative tests for potassium with sodium cobaltinitrlte,^66 With the hope that perhaps alcohol or some other organic liquid would In­ crease the rate and extent of precipitation of cobalt, the effect of three water-miscible liquids on precipitation was noted.These liquids were alcohol, dioxane, and acetone.

Procedure. A 300 ml. volume was used for each study and rate curves were obtained in the usual way when 25 and

50 ml. portions of these three liquids were added. The total volume was kept at 300 ml. each time. The data are in Table 29.

Results. The organic liquids tested gave no improve­ ment In the results. Dioxane, 25 or 50 ml., and 25 ml. of

acetone had no significant effect whatever on the extent of

orecipitation after 8 hour standing, and the value of per

cent cooalt aoproached was the same as without organic

liquids. Instead of Improving the method, alcohol appar­

ently decreases the rate by reacting with the reagent or

some form of . The data are plotted In Figure 6 .

The initial rate for dioxane appears to be somewhat greater

than for water alone but this could be due to differences

In the rate of cooling of the two solutions following

the heating step of the standard method. Fifty ml. of

acetone behaved similarly except that the limiting value

of cobalt precipitated rose to 90% in the last few hours. 107

Table 29

The Effect of Organic Liquids on the

Precipitation of Potassium Cobaltinitrlte

Per Cent Cobalt Precipitated;

I.i quid Time in Hours Ml. 2 4 8 20 24

Dioxane 50 m l . 13.9 31.0 53.9 76.1 78.2 77.2

25 ml • 11.3 25.7 45.0 62.7 78.0 31.6

Acetone 25 m l . 24.8 41.5 58.2 73.5 78.9* 05.0

50 ml • 31.1 49.7 69.2 84.4 91.1* 95.3

Ethanol 25 ml . 0.0 2.3 6.5 15.8 25.0 26.9

50 m l . 0.0 0.0 9.0 10.4 25.2 30.3 Per Cent Cobolt Precipitated 100 H 80 40 60 20 T hEf e f e c t o fTi m e o nt hPr e e c i p i t a t i o no fCo b a l t O WaterO only □D i o x a n ea d d e d A A E t h a n o lad d e d XA c e t o n e a d d e d T hPr e e s e n c eo fO r q a n i c L i q u i d s . a sPo t a s s i uCo m b a l t i n i t r i t e . Fig. Fig. T i mi e nHo u r s

6 20

24 108 109

This was undoubtedly due to loss of solvent by evaporation

and consequent concentration changes.

Potassium Determinations

As mentioned on page 81, potassium Is often deter­ mined by a cobaltinitrlte precipitation. The methods are

empirical to the extent that a fixed procedure must be

rigidly followed and the details of the procedure worked

out for materials of known potassium content which are

quite similar to the unknowns. Determinations are usually

indirect, involving titrations of the nitrite or color­

imetric estimation of nitrite or cobalt. A recent paper

describes a radiometric method in which radioactive cobalt

is used as tracer.

Among the numerous articles which deal with the

important factors influencing results of the potassium

determinations are those of Piper^®® and Barkovic and

Bican-Fister.109 The latter authors mention:

1. Composition and age of the reagent solution.

2. Degree of stability of solutions with respect

to light and temperature.

3. pH and temperature of the reactive mixture.

4. Time of observation.

5. Purity of ethanol, if used. Etc.

The K/Na and K/Co ratios in the precipitate are

affected by these and other conditions. Generally speak­

ing the precipitate has the composition KxNayCo(K0 2 )g.nHgO* 110

The variables x, y, and n depend on the factors mentioned above•

To obtain some information about the precipitation of potassium by sodium cobaltinitrlte, some experiments were performed.

Procedure. An active cobalt solution was converted to sodium cobaltinitrlte (De Konick's reagent, see Appendix

IV). Five mg. quantities of potassium as the chloride were obtained by pipetting the required volume of a sol­ ution prepared from analytical grade potassium bicarbonate and hydrochloric acid (the solution contained 1 mg. K/ml.).

To each potassium solution was added 25 ml. of water and

10 ml. of the reagent. The mixture was stirred and allowed to stand at room temperature. After 1, 4, 8 , 16, and 24 hours samples were filtered using filter crucibles. They were then washed 5 times with 35% (by volume) ethanol, according to Piper's procedure.-*-®® The precipitates were then dissolved in dilute HC1, transferred to a 100-ml. volumetric flask, diluted to the mark and set aside for activity measurements in the liquid counter.

The activity of the precipitates thus obtained end treated and the time of standing are shown in Table 30.

Under the conditions given above, precipitation is com­ plete after 15 hours and the precipitates approach a con­ stant composition after 30 hours. The rise in activity after 30 hours was not due to continued precipitation of Ill

Table 30

The Precipitation of Dipotassium Sodium Cobaltinitrlte

in Potassium Determinations

Sample Standing Observed Net No. Period, Hrs. Activity* B* kgrfnd Activity

1 6 662 43 629 (Inc< ppt'n) 2 it 490 43 447 tt

3 15 1321 47 1274 (Com] ppt*n) 4 rt 1102 47 1055 it

5 24 1098 47 1051 ti

6 it 1238 47 1191 ii

7 ii 1016 47 969 tt

8 30 1098 46 1052 ti

9 tt 1106 46 1060 n n 10 it 1096 43 1053

11 40 1262 41 1221 ft

12 tt 1283 41 1242 it

13 n 1271 37 1234 ti

14 48 1268 37 1231 n

15 it 1249 37 1212 ti

« Average of 10 minute counts. 112 potassium (as shown by the formation of no more precipi­ tate in the filtrates on standing). It was apparently due to a decrease of the K/Co ratio as the precipitate

aged which would confirm the statement of Boissier and

Hoyos,-1-^0 who said that some tripotassium cobaltinitrlte forms initially and is slowly converted to the dipotassium

sodium salt by reaction with sodium cobaltinitrlte:

Na3Co(N02)6 + 2 K3Co(NOg)6 3 KgNaCo(N0 2 )6 .

Summary

1. A review of the cobaltinitrlte method for cobalt is pre­

sented in which the nature and uses of this separation

as well as recent work on the method are discussed.

The use of the reaction in potassium analysis Is re­

viewed briefly and other possible apolications are

pointed out.

2. Very little information appears in the literature con­

cerning the rate of precipitation of cobalt by potassium

nitrite. A study of such rates was made under widely

differing conditions of volume, concentration of cooalt

and reagents, temperature, and presence of other mater­

ials. The extent of precipitation is easily followed

by the use of radiocobalt.

3. Except under extreme conditions of volume or concentra­

tion, the precipitation is generally quantitative In

less than the usually recommended 24 hour or overnight

period. From a total volume of 200 ml. or leas, amounts of cobalt up to 1 gram could be quantitatively separated

In 1 hour by 20 grams of reagent, other conditions being as given oy Scott.4®

The standard method was followed in separating 25 mg. quantities of cobalt from large quantities of nickel, copper, zinc, and cadmium (0.5 grams of each). In every case precipitation was quantitative in at least

1 hour.

When normally Interfering elements such as zircon!urn, thorium, tin, iron, antimony, aluminum, chromium, etc., are present, Kallmann’s procedure®^ was quite satis­ factory for the separations, which were quantitative within one hour.

The following procedure is recommended. It appears to cover most situations in which the cobaltinitrlte method is used In cooalt analysis* a. The sample should contain 0,5 grams or less of cobalt. b. Remove oxidizing agents ana free mineral acids from

samples; this is usually done by evaporation to

dryness. c. Mask easily hydrolyzable Ions by adding tartrate or

fluoride. d. Addition of acetic acid and heating are as described

in Scott’s standard method.48

e. In the preparation of the reagent use at least 20

grams of potassium nitrite plus 1 additional gram 114

for each, ml, of solution that Is present in excess

of a total reaction mixture volume of 200 ml. Large

volumes may sometimes be necessary to accomodate

large amounts of other materials present,

f. Let stand in a cool place, 20° C., for 2 hours. All

precipitations carried out in the present study were

quantitative in 2 hours when these conditions were

m ct •

7. Precipitation of cobalt as KgNaCo(NOg)g and K^CotNOgJg

under comparable conditions showed that the former pre­

cipitation has no advantages over the latter and 13 in

fact less sensitive. This is in contrast to suggestions

in the literature-*-^ perhaps Decause early workers had

access to relatively pure NaNOg but not reagent grade

KNOg.

8 . The addition of acetone or dioxane did not significantly

affect the rate of precipitation of potassium cobalti-

nitrite. Although ethanol is said to increase the sensi­

tivity of qualitative tests for potassium, where sodium

cobaltinitrlte is used,*0® it decreased the rate at

which cobalt is precipitated as the cooaltinitrite•

9. A simple experiment showing the rate of precipitation

of potassium by sodium cobaltInitrite and indicating a

change of precipitate composition on aging was carried

out. It further illustrates the value of radiometric

studies of this type. Many of the numerous specific 115 applications of the cobaltinitrlte method for potassium could be investigated in this way. SOLUBILITY LOSSES DURING GRAVIMETRIC DETERMINATIONS

In addition to information on the beet weighing

forms and drying temperatures of cobalt precipitates, such

as that of Duval,7 it is also important to know the opti­ mum conditions for precipitation and washing of precipi­

tates. Two of the Important methods for cobalt were in­

vestigated with regard to the soluoility losses that are

incurred during the analyses:

The Potassium Cobaltinitrlte Separation

In the previous chapter information was given con­

cerning the conditions for the precipitation of the cobal-

tinitrite, but nothing was said of the solubility losses

that occur during the washing of the precipitates. Wash­

ing is usually done with a weakly acidic potassium nitrite

solution or a potassium acetate solution, apparently be­

cause water will dissolve appreciable amounts. The only

solubility data for potassium cooaltinitrite in the lit­

erature appear to be that of Pierrat,111 who gave a value

of 0.21 gram of salt per liter, and of Rosenbladtwho

gave 0.89 gram per liter. An attempt was made to determine

the actual value.

The Solubility of Potassium Cobaltinitrlte. The

salt W 33 orepared as in Scott’s standard method (see p. 8 8 )

by adi.ing a large excess of reagent to 25 ml. portions of

the #3 cobalt solution, which had been made slightly acidic

with acetic acid. After an overnight standing period, the

1 1 6 117 precipitates were filtered, washed six times with 1 0 # potassium acetate, three times with absolute ethanol and dried for one hour at 110° G, About 0.2 gram was then placed in each of three 50-ml. glass stoppered cylinders containing 50 ml. of double distilled water. The stoppers were sealed with wax and the cylinders were placed in a constant temperature water bath where they were agitated continuously by being turned end-over-end on a spindle.

After 18 hours a cylinder was removed, a portion of the liquid was filtered, a 1 0 -ml. aliquot was pipetted into a 1 0 0 -ml. volumetric flask, and the cobalt in the solution wps determined by liquid counting. The unused portion of solution was resealed and returned to the water bath.

This procedure was repeated after longer agitation times with the expectation that a saturation value would be found. A constant value was not obtained. Prom the weight of cobalt, the weight of K3 Co(N0g)g per liter was calcu­ lated and the values are tabulated in Table 31.

These results were due to the decomposition of the precipitate rather than a reversible solubility equilib­ rium. This confirms the report of Burgess and hamm,^ that varying results of cobaltinitrite solubility measure­ ments are due to such a decomposition (see page 94).

A Comparison of Losses In Water and Potassium Acetate

Solution. To compare the losses that are encountered when

water or salt solutions are used for washing, precipitates Table 31

The "Solubility" of Potassium Cobaltinitrlte In Water at 25° C.

Hours Net Activity* Cobalt Calculated Per Liter Grams Salt Agitated Counts/Min. Grams Per Liter

18 1716 0.0094 0.721

25 1909 0.0104 0.799

42 2458 0.0134 1.05

48 2593 0.0142 1.09

90 37 60 0.0206 1.59

120 6052 0.0331 2.54

Activities of a 10 ml. portion. 119 of potassium cobaltinitrltet as prepared above, were agi­ tated for 15 minutes with 100 ml. each of water, and 10% potassium acetate. The mixtures were filtered and the cobalt in solution was determined by activity measurements.

The results in Table 32 show that 5 to 10 times as much cooalt is lost when water is used than when potassium acetate solution is used.

The results of the solubility study indicate that a "saturated potassium cobaltinitrite solution" cannot be used for washing precipitates, since a saturated solution of the salt cannot be obtained.

Typical Determinations. To evaluate the approximate magnitude of losses encountered in routine separations by potassium nitrite, six 25 mg. samples of active cobalt were precipitated and washed according to the standard procedure.

The wash solutions, 10% potassium acetate (6 washings with

10 ml. portions) and absolute ethanol (3 washings with

10 mi. portions), were collected, counted and the losses evaluated. The procedure followed was that given above, irecioitates were filtered into weigned Selas Triicroporous filter crucibles and after the alcohol wash, were dried

at 110° C. for one-half hour periods to constant weight.

Under these conditions the weighing form is said to be

K3 C0 {NO2 )6 »^ the results shown in Table 33 were def­

initely low, probably due to the presence of some Co.^O^’xhgO

in the precipit 9te. ^ 3 ISO

Table 32

Losses of Potassium Cobaltinitrite on Washing

with. Water and ± 0 % Potassium Acetate

Washed with Net Activity Cocalt Dissolved Salt 1 0 0 ml. of: Count s/Min. Mg. Dissolvt Mg-

Hg° 590 0.32 2.5

1365 0.74 5.7

1171 0 . 6 6 5.1

1 0 ^ 115 0.06 0.5 KOAc 102 0.06 0.5

80 0.04 0.3 121

Table 33

Solubility Losses of Cobalt

in Cobaltinitrite Determinations

Co Co Cobalt Losses » Mg. Net Per Taken Found KOAc Alcohol Cobalt Cent Mg. Mg. Filtrate Wash Wash Found Error

24.77 24.80 0.00 0.01 0.00 24.81 0.16

24.77 24 .32 0.00 0.01 0.00 24.33 -1.78

24.77 24 .68 0.00 0.00 0.00 24.68 -0.36

24 .77 24 . 61 0.00 0.00 0.00 24.61 -0.65

24 .70 24 .51 0.00 0.00 0.00 24.51 -0.77

24.70 24.4 6 0.00 0.01 0 .03 24.50 -0.81 122

The Double Ammonium Phosphate Method

A good review and critical study of the phosphate method for cobalt, Including a description of cooalt-nickel separations, was given by Schoellerf11® whose procedure is described in detail in the text of Gumming and Kay.11*

This procedure calls for a determination of small amounts of metal left in the filtrate and a corresponding correc­ tion. The method used in micro determinations was described by Strebinger and Poliak.ll!^ Dick116 did some work on the washing and drying of precipitates, while in some earlier work Dufty11^ mentioned that losses of cooalt in the fil­ trates could be as much as 1 mg* Krause-*-1® studied the optimum conditions for precipitation and his conclusions

are somewhat the same as those of Schoeller. Krause men­

tions how iron can be removed and also suggests an indirect

precipitation titration method for cobalt that is based on

the double phosphate precipitation. A procedure for the

separation of small amounts of cobalt from nickel by the

phosphate method was given by Goldstein.11^

Krause11® used a 5% ammonia wash solution and Dick11®

used a 0.5% solution of (NH4 )2HP04 followed by alcohol and

ether. Kolthoff and Sandell100 say, ''..washing with water

doe3 not lead to any appreciable solubility loss.." Scho­

eller also washed precipitates with water.

Precipitates may be dried as CoNH4 P04 'iigO at 115°

to 120° C.11® or ignited to the pyrophosphate. 123

Although much work has been done with regard to the proper amount of excess reagent and the washing and drying technique, the optimum pH for precipitation has not been stated specifically. Cumming and Kay^-^ came closest to a definite statement of pH In their procedure where pre­ cipitation was made in a solution which gave a green color with Dromtnymol blue. This would be approximately a neutral solution.

The Effect of pH on Solubility Losses. The procedure followed was quite similar to that of Cumming and Kay, ex­ cept that the amount of ammonia added was varied in order that the pH effect could be studied. Twenty-five milli­

liter portions of cobalt solution #7 were pipetted into

250-ml* beakers. Five ml. of concentrated HC1 and 0.33

gram of (NH4 )gHP04 dissolved in 25 ml. of water was then

eddea to the cooalt. The mixture was heated nearly to

boiling and ammonia solution (2:5) was added with stirring until a oH of about 0.2 or 0 . 3 units greater than that to

oe tested was attained (measured by pH meter). During

this addition a light blue precipitate formed which was

probably the phosphate. The solution was kept hot, but

not boiled, for 3 5 minutes, then the beaker was removed

from the heat and allowed to stand overnight. During the

heating and standing periods the light blue precipitate

changed into the light purple double ammonium ohosphate,

and the oH decreased, due to ammonia losses and the re­ 124 action, to approximately the desired value. After the standing period, the precipitates were filtered into weighed filter crucibles. The pH of the undiluted filtrate was measured and It was transferred to a 1 0 0 -ml. volumetric flask, diluted to the mark, and set aside for liquid count­ ing. The precipitates were washed with three 20-rrJ. • por­ tions of cold water, the washings were collected, and were also counted. After washing with acetone, the precipi­ tates were dried in the oven at 115° C. to constant weight.

The data of these determinations are recorded in Table 34.

Figure 7 shows a plot of the filtrate losses vs. final pH at which precipitation was made. It Is seen that the losses are at a minimum in the pH range 7.2 to 7.5.

At pH1s below 6.5 the soluoility increases rapidly due to the absence of ammonia and phosphate as P0^“^. Above a oH of 8 the solubility again Increases, this time due to the presence of excess NH^ and the tendency of cobalt to remain In solution as the ammino complex.

For precipitations carried out in the optimum pH range, cobalt losses on washing with cold water are of

About the same magnitude as the filtrate losses.

The error of determinations based on wel diing the precipitate as CoNH4 P0 4 *H20 passes through a minimum be­

tween oH 7.27 and 7.92. The net error however, shows an

Increase from negative to positive values as the pH is in­

creased, with best results in the optimum pH range, 7.2-7.5. ±aole I

tiOlu L)-i_ * L*1V AjO *.> ^jO l.J Jo. al. in Deter, inations by the Doable Pi .o collate Letiiod

.u. Cobalt Cobalt Cobalt Losses in: Let Cobalt bet *">' ’ "1 *f 1 ^ p of Tahea in iytsa Orror A --- 1 l> A > r 0* s.05 ■t, » jhr } 1 ' O' 1 ' ^ 0. _ai- -0,60 v O w ■j * Xo ii *r-'t? nr ” *w'|b'. V 4 ^X L:.C'5 * r / • a*-' 0.04

'r n } r, r* • - j ‘r , • .2 “ . ..13 - »U( 4:.05 -0.39

ii / . or ' 7 r 0.05 V •::? * r , • .V ; •>- « „, v ,09 0.11 49.59

. > | r ii M ; ' i oo l ■ 'r / -.0? ,.l0 V .43 -0.11

1 f) n ( • '> / a , . to - 0 . ^ 7 0, .'lj 49.47 -0.07

% ii /, i / i i ( « - J • r ✓ • - v - o'-.u6 o,l.9 04 4 00 49.75 0.21 r; o') it j • /*- • t V . 39 - o.l5 ■„.n 0.13 49.63 0 . 0 9 i-/ * oU it 43.17 -0,(■ j{"’i o.45 0 . 0 3 4t *65 0.11 .o :. /5 m / • O ,9 -O.oj' 'm • -_J*- 0 . 0 3 49.70 0.16 a ^alculated usin;- the I actor Co/CohiujPOi/iijG 125 Mg. of Cobalt Left in Filtrate 0.6 0.4 0.8 02 - h Efc o p o Slblt Lse o C0NH4PQ4 of Losses Solubility on pH of Effect The i. 7 Fig. pH 136 127

A similar effect was noted by Ball and Agruss^ 0 in zinc determinations•

A Comparison of Losses in Various Solutions. Pre­ cipitates of cobalt ammonium phosphate prepared at pH 7.5 were agitated for 15 minutes with 100 ml. each of the sev­ eral different solutions that have been suggested for washing. After filtration, the cobalt content of the filtrates was determined by liquid counting. The losses are compared in Table 35.

From these results it is noted that 5% NH-j solution should not be used for washing. The organic liquids give no appreciable losses. The loss when water is used is about 1.5 times that when 0.5^ (NH^)gHPO^ is used for wash­ ing. The latter could be used to aovantage without causing coprecipitation errors if the ignition method of obtaining the weighing form is used. 128

Table 35

Losses of Cobalt Ammonium Phosphate

on Washing with Different Solutions

Wash Sol*n3 Total Net Cobalt Lost 100 Ml. of: Activity* Bkgrnd Activity Mg.

5# nh3 1311 43 1268 0.91

Water 330 43 287 0.20

0.5# (NH4 )2HPC>4 227 43 184 0.13

65# Ethanol 80 43 37 0.03

95# Ethanol 41 43 - 2 0.00

Acetone 46 43 3 0.00

Ether 41 43 - 2 0.00

Average for a 30 minute count.

** Calculated from the solution specific activity of

the cobalt used in this study, 1386 C./Min./Mg. RADIOMETRIC TITRATIONS

Radiometric titrations are similar to conductometrie or amperometric titrations. In radiometric work, measure­ ment of the change in concentration of radioactive mater­ ials in solution makes it possible to follow the course of the titration reaction. This is comparable to the measure­ ment of electrical conductivities or diffusion currents.

The three methods have in common the fact that the inter­ section of portions of the titration curve (usually straight line portions) determines the end point; in all the methods the reagent solution should be considerably more concen­ trated than the solution being titrated in order to give a small volume correction.

Previous Work

Radiometric titrations which have been described In the literature include those of magnesium, uranium, phos-

1 < J * ] phate, silver, and the halides, reported by Langer,■L,C'L and of chromium, molybdenum, and vanadium given by Govaerts and Barcla-Goyanes.^-^^ A method for fluoride was recently described in a paper by Onstott and Ellis.The last mentioned authors gave a short review of the Development of the method ana pointed out the advantages and disad­ vantages. Apparently no radiometric titration procedure has been described for cooalt.

A review was made of precioitation titrations which have been reported for cobalt. It was felt that the

129 130 radiometric method might be of value in improving some of these methods. In some early work, it was reported that

cobalt could be determined by titration with ferrocyan-

ide.124 The titrations were carried out in the reverse manner, i.e., cobalt was added to the ferrocyanide. Other

work indicated however, that the composition of the product

varies with the order of addition of the reagentsl^b an(j

with other reaction conditions.-*-2® Hence, the reaction is

not suitable for quantitative work. Similar difficulties

are encountered In attempting to titrate cooalt as Co(CN)g “ 3

with the heavy metals.-*-27

A determination by oxine based on the end point

detection by a filtration method was reported by Bucherer

and Meier,^-28 but difficulties In volume control would

make titrations with this reagent difficult.

The reaction which appeared to be most adaptable to

radiometric rethods was that of cobalt with l-nitroso-2 -

naphthol In a weakly acidic solution (acetic acid),

holthoff and Langer*-^ reported cobalt titrations with

this reagent in which the end point was determined amper-

ometrlcally. This reagent has also been successfully

aoplied to volumetric determinations of iron^29 anci zir­

conium.*-^®

Apparatus. The scaler, GM tubes (TGC-6 and D-b2),

and the centrifuge used in this study are described In 131

Appendix IV. A small glass vessel was constructed which could be clamped in position such that the GM tube was jacketed by It. This vessel had a capacity of about 12 to 15 ml. and could be filled by suction with a special rubber bulb (page 174) on the upper end, while the liquid entered through a tygon tube, one end of which was attached to the lower outlet of the vessel and the other end was placed in the container in which the titration was per­ formed. This arrangement Is shown In Pig. 8 . The GM tube could be surrounded by a thin layer of the active liquid without being in contact with it. After a reading was taken, the liquid could be returned to the centrifuge tube (separated from the counting tuoe by lead brick) by releasing the valve on the rubber bulb. The apparatus was flushed with solution and refilled before the next

reading.

Heagents. The reagent solution consisted of 17

grams of 1 -nitroso-2 -naphthol dissolved in 60% acetic

acid and diluted to 1 liter with 60% acetic acid. A small

residue was filtered off and discarded. This solution was

almost saturated with resoect to 1 -nitroso-2 -naphthol.

Procedure. Before a titration was begun, the vessel

was filled with water and a Dackground count was obtained.

A cobalt solution (solution #5, page 1B0) was pipetted

into a 200-ml. centrifuge bottle and 150 irl. of water were

sdaed. Pour and two tenths grams of sodium acetate tri- /3Z

a p p a r a t u s u s e d f o r t h e radiometric t i t r a t i o n s 133

hydrate were added and dissolved. This was followed by the

addition of 1 ml. of glacial acetic acid and 10 ml. of the

carrier free Co60 solution (page 180). The resulting sol­ ution was about 0.1 M in acetic *cld and 0.2 M in sodium

acetate. The solution was well mixed by the use of a mag­

netic stirrer bar.

The initial count was talcen by placing the bottle

to the right of the lead bricks and filling the counting

vessel by using the pipet filler bulb. After the count

the solution was returned to the centrifuge bottle which

was again placed on the stirrer.

With the stirrer turned on, a portion of reagent was

slowly added from a buret (preferably one with a grease-

less stopcock). The solution was stirred for about 5 min­

utes, centrifuged at 800 rpm for about 5 minutes, and the

counting vessel was filled for the second count.

This process was repeated several times during a

titration. The stirring oar was left in the bottle during

the titration. To make volume corrections on the data, it

was necessary to record the total volume of solution init­

ially as well as the volume of reagent used.

The counting vessel could be cleaned and dried very

easily by rinsing with acetone and by passing air through it.

Discussion

Some difficulties were encountered during the cen­

trifuging operations. Large volumes of solution are 134 necessary to reduce the volume correction, but in large centrifuge tubes there is a tendency for eddy currents within the solution during the centrifuging operation, with the result that some precipitate is not thrown to the bottom. These currents appear to originate during the last few turns of the centrifuge oefore it stops, and a careful slow-down of the centrifuge helos eliminate this difficulty.

It was necessary to allow the solutions to be stirred for about 5 minutes after reagent additions. If this was not done, a finely divided suspension remained In the super­ natant liquid after it was centrifuged. This was espec­ ially true after the first 2 or 3 reagent additions. The addition of 2 or 3 drops of a 5% gelatin solution did not facilitate matters.

The reagent solution is standardized by titrating a known cobalt solution in this manner. According to

Kolthoff and Langer, the reagent can be used for about

3 weeks after a standardization. In the present work it was observed that some solid material collected on the bottom of the reagent bottle after about 1 month, and during this time the titer for 10 mg. of cobalt increased from 11.7 to 18.6 ml. The titrations indicated by "A11 were made with fresh reagent, those marked "B" were made with the one month old reagent from which the solid was

removed by filtration. 135

Since only one other count in addition to the init­

ial reading will give a straight line and fix the end point, rapid but less accurate determinations could be done very easily. They were performed as described previously, ex­

cept that the titration vessel was a 250-ml. beaker. The

initial count was taken as usual. After the reagent was

added and the solution was mixed, a 50-ml. portion was

decanted, centrifuged in a clinical centrifuge with 50-ml.

tubes, and counted. The large centrifuge and the 200-ml.

bottle3 were therefore not needed for these r,2 point"

titrations•

Results of the Study

Five and 10 mg. cobalt samples and a cobalt-nickel

mixture consisting of 5 mg. of cobalt and 10 mg. of nickel

were titrated by this method. The data are given in Table

36, and typical curves are .>hown in Figures 9 and 10. The

end ooint values were determined graphically, except for

the "2 point" samples, in which they were calculated by

the slope intercept method. The results may be summar­

ized as follows:

Osin’ reagent "A":

10.00 mg. Go 11.15 ml. reagent required

10.00 " 11.35 ml. " "

10.00 Mg. Go ("2 pt.") 12.18 " «

10.00 " » 11.90 » «

Av. 11.65 ml. 3.5%. 136

Table 36

Radiometric Titration Data

Total Reagent Total Back- Dead Net Net Count Volume Added Count ground Time Count x(V+v/V) V Ml, v Ml. C./M. C./M. C./M. C./M.

10.00 Mg. Co, D-52 GM tube, Reagent "A", "2 point" samples,

*167 0 . 0 0 0 9253 36 105 9322 9322 169 2.000 7592 ii 73 7 629 7758 171 4.000 5820 n 42 5826 5966 173 6.000 4066 it 21 4051 4197 175 6.000 2479 •i 6 2449 2566

167 0 . 0 0 0 9305 36 107 9376 9376 169 2.000 7634 ii 73 7671 7763 171 4.000 5930 it 44 5938 6081 173 6.000 4200 it 21 4135 4335 175 8.000 2 616 ii 8 2588 2712

167 0 . 0 0 0 9275 36 105 9341 9341 172 5.000 0346 it 35 5345 5504

167 0 . 0 0 0 9520 36 105 9389 9389 172 5.000 5288 it 33 5265 5442

•fco.00 mg. Go, TGC-6 , "B it »

167 0 . 0 0 0 7918 27 79 7970 7970 170 3.000 5516 ii 38 5529 5628 ti 173 6 . 0 0 0 2845 10 2828 2927 it 176 9.000 247 0 220 232 179 12.00 28 it 0 1 1

^*■5 . 0 0 mg. Go 10.0 mg. Ni, TGC-6 tube , "B»,

167 0 . 0 0 0 7918 27 79 7970 7970 169 2.000 6941 it 61 6975 7060 171 4 .000 4962 it 30 4965 5083 ii 175 8 . 0 0 0 1404 3 1380 1447 179 12.00 36 ii 0 9 10

cont'd next page

Graphed In Pig. 9.

Graphed in Pig. 10. 137 Table 36 cont'd

Radiometric Titration Data

Total Reagent Total Back- Dead Net Net Count Volume Added Count ground Time Count x(V+i V Ml. v M l . C./M. C./M. C./M. C./M.

10*00 mg Co, D -52 tube , "B",

172 0.000 9080 40 104 9144 9144 177 5.000 6589 it 55 6605 6790 182 10.00 4040 it 20 4020 4275 187 15.00 1563 ti 4 1526 1659

10.00 mg . Co, same conditions,

172 0.000 9073 30 104 9147 9147 180 8.000 4956 n 31 4957 5188 188 16.00 920 ft 2 888 971 Activity, Counts / Minute 2000 0 0 0 4 10 0 0 0 8 0 0 0 6 , 0 ' l o Raet Added ReagentMl. of oimti T Rodiometrici Cobalt trot of ion ih Nirs--Naphthol I N -with itroso-2- 10 mg. Co o 1 ? F19 1 1 m reagent 11.15 ml

8CT Counts / Min ute 10,000 0 0 0 8 0 0 0 6 0 0 0 4 2000 Ml. of egn Added Reagent aimti Ttain f Cobalt of Titration Radiometric 5 mg. Co 5 O fet f Nickel of Effect I - Nitroso - 2~ Naphthol 2~ I -Nitroso - ft,. ft,. 16 H 140

Using reagent "B":

5.00 mg, Co 9.32 ml. reagent required

10.00 " 18.80 ml. H "

10.00 " 18.05 m l. " '*

Av. 18.50 ml./lO mg. rf-al.73^

5.00 mg. Co 10.0 mg. Ni required 9.52 ml.

In the titration of the cooalt-nickel mixture, the cobalt appears to be held oack somewhat during the first part of the titration but approaches the correct value as the titration proceeds (Pig. 1 0 ). Nickel was reported to interfere with the amperometric end point,13 but the magnitude of the error was not given.

Conclusions

The end point of titrations of cobalt with 1-nitroso-

2 -naphthol in a solution buffered with acetic acld-acetate may be determined Dy radiometric means, but the accuracy

of the method is only about 2 to 4% compared to the 0.5/t>

reported for the amperometric end point. In those instances where easily oxidizable or reducible substances are present

and interfere with the amperometric end ooint, the radio- metric method would be advantageous.

The chief advantage of radiometric over amoerometric

methods lies in the fact that In the latter method the

diffusion current is directly proportional to the quantity

of substance being determined (or the reagent being used),

while In the former method, although the measured quantity 141

(activity) is proportional to the concentration of constit­ uent sought (or the reagent) in a given titration, the

activity can be adjusted before the titration by adding

the desired amount of radiotracer.

Radiometric methods have certain advantages over

conductometric methods: (1 ) only the radioactive species

and not all ions present determine the magnitude of the

measurement, i.e., the addition of foreign ions has no

effect; (2 ) temperature variations do not affect the

accuracy of the radiometric end point very seriously.

On the other hand, radiometric titrations have the dis­

advantage that there must oe a removal of the reaction

oroduct from the system. They have previously been re­

stricted to precipitation reactions, but there Is a pos­

sibility that reactions in which a product or the excess

reactant can be separated from the titration system by

a liquid-liquid extraction, may also be used for radio-

metric titrations. THE SOLDBILITIES OP COBALT ANTHRANILATES

Punk and coworkers131 have shown that anthranillc acid Is a good organic reagent for cadmium, cobalt, copper, lead, manganese, mercury, nickel, silver, and zinc. Studies

of the pH range for precipitation of the various metals by this reagent were mace by Goto13® and by Harris.133 Al­ though the reagent Is not very selective, the precipitates

are clean, easily filtered, and easily dried. In addition,

the gravimetric factors are favorable, e.g., for cobalt it

Is 0.1780.

There has been very little investigation of the der­

ivatives of anthranillc acid as reagents for quantitative

analysis. The use of some of the halogen substituted der­

ivatives as reagents for metals was reported by Shennan134

and by Bhatki and Kabadi.133 In a study of the effects of

substituting Iodine and bromine In the aromatic ring of

the acid, Romero13^ determined the pH range of precipita­

tion of metal 5-iodoanthranxlates, Zehner and Sweet deter­

mined iron by a spectrophotometrlc method in which 5-sulfo-

anthranillc acid was used.136 Harris and Sweet138 recently

reported the stabilities of the copper and cadmium che­

lates of anthranilic acid and five of its derivatives.

The relative tendencies to chelate is a factor in­

volved in the 3olu'oility of metal anthraniiates, and s o l ­

ubilities have been used oy some Investigators to study

this factor.139 Solubilities are also of considerable

142 143 value In the development of separation procedures.

The only solubility data for metal anthranilates that have been reported by previous workers were those for the 5-iodo ant hr anil at es, given by Romero^^ and of copper anthranilate at various pH values.73

The work of Harris133 indicated that dlanthranilic acids were promising analytical reagents, and W.A. Young14*-* has prepared several such compounds. The acids used in the present work included those prepared by Romero*137

Harris,133 and Young.14^*

The Measurement of Solubilities

Radiotracer techniques have been aoplled to sol­ ubility studies for many years. Hevesy and Paneth141 reported such studies for uranium compounds as early as

1913. A review of the radiotracer methods as well as a

survey of all the important methods of solubility deter­ mination was given recently by Zimmerman,14^ The contin­ uing interest in and importance of the method is shown by

recent work, such as the data of Voskresenskaya143 on

thallium compounds, in which Tl^ 4 was used as a tracer.

Very little work has been done on the determination

of solubilities of cobalt compounds Dy means of radiotra­

cers. By using cyclotron produced cooait-60, Cacciapuoti

and Ferla144 determined the solubilities of cobaltic hydrox­

ide, cobalt l-nitroso-2 -naphtholete, and cooalt 2 -nitroso-l-

naphtholate. Very recent work in this department on the 144 solubilities of certain cobalt complexes In organic sol­ vents^-4® appears to be the only other solubility data ob­ tained by radiotracers for cobalt compounds.

Experimental

The present work on solubilities consisted of the following three steps: (a) the preparation and purifi­ cation of labelled cobalt anthranllates; (b) the prepar­ ation of a saturated water solution of these compounds, and (c) the determination of the amount of cooalt In the

saturated solutions by activity measurements. A discuss­ ion of each of these steps and a description of the pro­ cedures used is given below.

The Preparation of the Cobalt Compounds. There are no procedures in the literature for the precipitation of metals by most of the reagents Investigated in the present work. The procedures that were tried first were as nearly

as possible the same as that given in the literature for 1 anthranilic acid. In some cases this had to be mod­

ified oecause of reagent Insolubility or because a precip­

itate was not formed under these conditions. The pH chosen

was 4 .4 , the value at which cobalt is just precipitated by

anthranilic acid.^22 If necessary, higher pH's were used

In attempts to Increase reagent solubility and produce ore-

cipit ates.

The preparations were on a small scale; the amount

of active cobalt used In each study was limited to 10 ng. 145 since greater amounts gave unnecessarily large amounts of activity.

Procedure. Five ml. of active cooalt solution were pipetted into a 250-ml. beaker and 10 ml. of double dis­ tilled water were added. The pH of this solution was ad-

lusted to 4.4 (pH meter) by adding 20% sodium acetate.

Twenty ml. of a buffer solution were added. This buffer

solution was prepared by adding glacial acetic acid to

20% sodium acetate until the pH was 4,4, as Indicated by the pH meter. The beaker was then placed on a water

bath and heated to near boiling (^95° C.).

The reagent, 0.18 gram of anthranillc acid or its

derivative, was weighed out and placed in a graduated

test tube. Three molar NaOH was added, with stirring,

until the reagent dissolved. Water was adoed until the

volume was 6 ml. This 3% solution of the reagent was

adaed dropwise with stirring to 20 ml. of the pH 4.4 ouffer.

If reagent began to crystallize out during the addition,

no more reagent was added to the buffer; that which crys­

tallized out was filtered off. The amount remaining in

solution was estimated from the volume of reagent solution

that had been used.

The buffered reagent solution was then added drop-

wise to the hot buffered metal solution and the mixture

was allowed to digest on the water oath for 6 hours. The 146 precipitate was filtered by suction filtration using Selas microporous filter crucibles.

The cobalt compounds were washed 3 times with hot water to remove acetate, 3 times with absolute ethanol

and twice with ether to remove unreacted reagent, and finally sucked dry. The crucibles and contents were placed

in a ]10° C. oven for j hour.

Since the cobalt compounds were quite active, it was necessary to handle the oowdered products with care.

They were removed from the crucibles and placed in labeled

glass vials which were stoppered with tight-fitting poly­

ethylene stoppers. Transfer operations during preparation

and use were made in a well ventilated hood.

Unfortunately most of the substituted anthranilic

acids that were investigated were less soluble than the

anthranilic acid and the solutions of tneir sodium salts

had to oe iess than 3%. The use of larger amounts of

NaOH in the initial dissolving step did not improve mat­

ters since the acids crystallized out when they were added

to the ouffer solution. The work of bhatki and Xaoadi^^

sug rested that an ammonia solution might offer advantages

over NaOB and some experiments were made in which ammonia

was used for dissolving the reagent. Other attemots to

get better results were: (1 ) the use of the same orocedure

that is ;ziven aoove, but raising the pH to 0.8 (the upper

limit for the acetate buffer) and, (2 ) trying precipita- 147 tlon from an ammonlacal solution from which ammonia was slowly expelled by boiling (no acetate present). All of the experimental work performed during preparation of the cobalt compounds, and the corresponding results are summar­ ized In Table 37.

The Preparation of Saturated Solutions. After a labelled cobalt compound was prepared and purified, a por­ tion (about 30-40 mg.) was placed into a cylindrical glass-

stopoered agitation tube (capacity <-^95 ml.) along with

80-85 ml. of triple distilled water, which had been sat­ urated with nitrogen. The air remaining in the tube was flushed out with nitrogen and the glass stoppers were In­

serted and sealed with paraffin. Ruboer bands were also used to help hold the stoppers in place and prevent move­ ment during subsequent agitation. The exclusion of air

by nitrogen was done to preclude the possibility of air

oxidation of the -NHg group of the compound. A coat of

opaque paint on the outside of the agitation tuoes pre­

vented the action of light on the compounds during the

long agitation periods.

With the circulation motor on, the water bath con­

taining the agitation motor and spindle was adjusted to

a temperature of 25.0° C. Temperature control was by

means of circulating colo water and knife-blaae heaters.

These were controlled by means of an electronic regulator

and mercury capillary contact switch, ana could be checked 148

Table 37

Preparation of the Cobalt Compounds of Anthranilic Acid and Several of its Derivatives

Reagents Procedures Tried, Conditions, Description et c. of Compounds

Anthranilic Acetate buffer, pH 4.4a Pink flaky acid (A «A.) Activities shov/ed*-*99% of solid the cobalt was potd.

N-methyl A.A. Acetate buffer, oil 4.4 5.8. No cpd. formed

N-phenyl A.A. Reagent insoluble in solutions No cpd. formed of pH 10. Tried solutions of pH 4.4 & 5.3 with 0Ac“ buffer, and 7 5: 8 with no buffer. Reagent crystallized out, got hydroxides with pH over 8 .

Methylene Di Acetate buffer, pH 4.4, slow Light brown A. A. opt'n after 3 hours, digested ppt. More dense 6 hrs. v\70% of Co opt'd at pH than the an- 4.4 and 95% at pH 5.8. thranilate.

Ethylene Di Acetate buffer, pH 4.4 & 5.8 No cpd. formed A.A. gave no p )ts. Same procedure with no acetate but dissolved reagent in 2-3 drops ammonia, added to slight­ ly ammoniacal Co sol'n, still no pot even on evaporation of ammoni a.

Prooylene Di Same results as with ethylene No cpd. formed A.A. di A.A. Reagent less soluble, used 0.5% s^l'n. Nothing from ai’^oniacal sol'n.

o-(arinomethy1) Acetate buffer, pH 5.8 gave No cod. formed benzoic acid red-pink sol'n, no ppt. No out on evaporation or from amoniacal 3ol'n.

cont'd next oage 149

Table 37 cont'd

Preparation of the Cobalt Compounds of Anthranilic Acid and Several of its Derivatives

Reagents Procedures Tried, Conditions, Description etc. of Compounds

Hydrazo Di- Acetate buffer, pH 5.8? Sol'n No cpd. formed A.A. turned from bright yellow to red-brown on digestion, no ppt. Prom ammoniacal sol'n and from more concentrated sol'ns, still no ppt.

Bis Ammonia Same as with the above reagent.No cpd. formed Di-A.A.

5-3romo A.a . Acetate buffer, pH 5,8, Pink powder Co was 90£ pptd.

5-Iodo A.A. Same as with the 5-lodo. Pink oov/der

3 ,5-dibromo Acetate sol'n, oH 5.8 ,reagent A.A. was ^l^b, no ppt. Ammoniacal sol'n; 0.15 g. re­ Red-orown agent in 3 droD3 ammonia and flakes HgO. Added to 10 ml. of Co sol'n and 5 ml. conc. ammonia. Digest 6 hours, small red-orown oot. ^ 20% of the Co was ootd.

3,5-dliodo The same procedures as with the No cpd. A.A. 3,5-dibromo reagent gave no ppt. formed Some reagent came down on digestion.

3 -bromo, 5-iodo Using the same procedures as with No cpd. A.A. the di Br or di I A.A. gave no formed ppt. (acetate buffer of )

Prom a oasic tartrate solution, ? small trace of active opt. after three days standing (?).

a. The orocedure is described on oage 145. 150 by noting the reading of a Beckman thermometer. The tube containing the water and cobalt compound was attached to the spindle, and the mixture was agitated oy the end-over- end motion of the cylinder and solndle, which was about

5 turns per minute. A more detailed description of the soluDility apparatus, including diagrams, is given by

Hall.145

After several hours of agitation the motor was turned off, the cylinder taken out, the rubber band and wax seal removed, and a portion of the liquid filtered through a clean dry Selas microporous filter crucible into a clean dry filter flask. After flushing out the air and re sealing as before, the remaining suspension in the agitation tube was returned to the water bath for further agitation. Immediately after filtration, the suc­ tion was turned off, the crucible removed and a 2b-ml. portion of the filtrate oipetted into a 100-ml. volumet­ ric flask. The flask was diluted to the mark with dis­ tilled water and set aside for counting.

Further samples were collected after longer agita­ tion times and when the activity of the liitrates approached

a constant value, it was assumed that a saturated solution

had been produced. Table 38 shows the values of the sol­ ubility of cobalt anthranilate after various times of agi­

tation. 151

Table 38

The Effect of Agitation Time on the Water Solubility

of Cobalt Anthranllate at 25° C.

25 ml. of solution counted each time

Hours Time for Back- Solubility Agitated 10,000 Total ground Net Mg. of cobalt counts, C./M. C./m . C./M. per liter Min.

12 a 42.090 237.6 47.5 190.112.4 4 .278 +0.055

b 45.690 216.9 I! 171.4 *2.2 3.760 ±0.050

24 a 37.638 264.2 tt 216.7 ± 2.6 4 .865 ± 0 .059

b 42.780 233.8 186.3 12.3 4.182 +0.052

48 a 38.315 261.0 46.1 214.9 ±2.6 4.825 *0.059

72 a 37.567 266.2 " 220.1 ±2.7 4.916 +0.061

b 37.582 266.1 " 220.0 ±2.7 4.916 *0.061

c 21.372 463.0** " 421.9 *4.7 4.336 ±0.054

-sc- Showing the statistical error.

■m-** A 50 ml. portion of solution was taken. a, b ana c

represent three different tabes from which samples

were taken. 152 In work with subsequent reagents, the first samples were removed after 72 hours and it was assumed that these were also saturated* A check was made at 96 hours to be certain of this; additional assurance was given by the fact that samples from different tubes showed the same values after a 72 hour agitation period.

Counting. The procedure for liquid counting is given In Apoendix IV. In the solubility study, emphasis was placed on the accuracy of the count, i.e., long counts were taken to determine the "solution specific activity" accurately. The standardization data for the active sol­ ution are shown in Table 39. The total count taken each time was noted and the expected statistical deviations were calculated and are Indicated in the table.

Results

Solubility values were calculated from the observed

activities of the saturated solutions and the "solution

specific activity" (Dage 176) of the active cooalt sol­ ution. The data and the calculated results are shown in

Table 40. The five compounds that were successfully pre­

pared and studied were increasingly soluble in the follow-

inr order:

3,5-diBr cpd.^ A.A. c p d ^ MeDl cod.^ 5-Br c o d . ^ b-I cod.

From both the standpoint of the procedure for pre­

cipitation and the large solubllitv value, it appears that

the o ,b-dibromo acid is not suitable for analytical uses. 153

Table 39

Standardisation Data for the Active Cobalt

Solution Used in the Solubility Studies

Mg . Total Activity3 Back- Dead Net Activlty/Mg. Cobalt C,/l£in. ground Time C./Min./Mg.

2.982 5305 43 32 1772

1.988 3632 " 16 1815

0.004 1796 " 4 1759

Average 1782

a. This is an average of a measurement of 50,000 counts 154

Table 40

The Solubilities of the Cobalt Compounds

of Anthranilic Acid and Several of its Derivatives

Cobalt Per Cent Cobalt Net Activity Solubility Compound in Compounds: of 25 ml. of with: Theoretical: Found:® Solution Mg. Co/L.

Anthranilic 17.80#b 13.25# 220.0 ± 2.5f 4 .92 t 0.06 acid (A.A.) 17.72# 211.0 1 2 .5f 4 .84 1 0.06

220.0 ±2.5f 4 .92 1 0.06

Av. 4.89 ±0.04

5-bromo A.A. I2.06b 11.95 22.9 t 2 f 0.514 1.045

15.7 l2f 0.3531.045

14 .8 ±28 0.335 ±.045

18.9 l 2S 0.424 ±.045

A v . 0 .407 ±.022

5-iodo A.A. 1 0 .11b 9.89 8.1 ± 2f 0.132 ±.04

4.9 ±2f 0.108±.04

7.3 1 2s 0.161 ±.04

6.9 ± 2® 0.1521.04

Av. 0.151±.02

3,5-dioromo 9.12b 8.95 1160 ± 10f 25 . 5 +0.3 A.A. 1202 i I0f 26.4 i 0.3

Av. 25.95 ±0.2

cont'd next oage 155

Table 40 cont'd

The Solubilities of the Cobalt Compounds

of Anthranillc Acid and Several of its Derivatives

Cobalt Per Cent Cobalt Net Activity Solubility Compound In Compounds of 25 ml. of with: Theoretical: Found:a Solution Mg. Co/L.

Methylene 17.18#° 14.67# 26.8 0.602:1.05 Di A.A. 14.84 d 14 .45 14.20 e 14 .56 27.3- 2 0.6131.05 13.92 Av. 0.6081.04

a. Determined by dissolving weighed samples and counting

In the liquid counting apparatus to determine the cobalt

content. Good to about ±2#.

b. For the 2-1 compound in the anhydrous form.

c. For the 1-1 coinoounci in the anhydrous form.

d. For the 1-1 compound having 3 molecules of water of

hydration.

e. For the 1-1 compound having 4 molecules of wster of

hydration.

f. Agitated for 72 hours.

g. Agitated for 96 hours. 156

The fact that 3 ,5-dibromo anthranillc acid gives a cobalt oreclpltate while the 3,5-dilodo compound does not may be explained on the basis of the relative acidic prop­ erties of the two reagents.-*-37 The ability of halogen sub­ stituents to supply electrons to the aromatic nucleus and consequently decrease the dissociation of the acid has the order:

F > Cl > Br > I.*

The bromo derivatives, having a greater affinity for hydro­ gen ions, would also have a greater affinity for metal ions and would be more likely to form insoluble metal chelates.

The solubility of cobalt 5-iodoanthranilate given above, 0.151 mg. Co/liter, is considerably less than the figure given by Romero,^-37 which corresponded to 16.4 mg. of cobalt/liter. In order to further compare the radio- metric method with that used by Romero, a 25-ml. portion of saturated cobalt 5-iodoanthranilate solution wns evap-

This order was explained by Baddley and coworkers-*-4 6 in terms of the overlapping of the £ orbitals of the halogen atom and the carbon atom to which it is attached. The ability to overlao is directly related to the ratio of the radius of the halogen atom to the covalent bond radius.

The values of this ratio, R/r, were given: F, 2.15; Cl,

1.58; Br, 1.44; and I, 1*33. 157 orated to dryness in a weighed flask (Romero's procedure).

The residue weighed 0.000 0 gram compared to 0.0041 gram given by Romero, and it appears that his value is rather high.

The three reagents, methylene dianthranilic acid,

5-bromoanthranilic acid, and 5-iodoanthranilic acid, give compounds less soluble than the corresponding anthranilates and may be useful for the analysis of metals not easily precipitated by anthranilic acid. For example, manganese anthranilate is so soluble it is not easily determined by anthranilic acid.151 Hence, these three reagents may pos­ sibly be useful for the determination of manganese.

It Is surprizing that methylene dianthranilic acid precipitates cooalt while the ethylene and propylene homo­ logs do not. It is felt that the analytical applications of this reagent should be investigated further. SUMMARY

Cobalt-60 was used as a tool In. a study of certain phases of the analytical chemistry of cobalt:

An anodic deoosltlon method for the determination of cobalt was developed that utilized the Isotope dilution technique. The advantages of the technique eliminated incomplete deposition and non-adherence of the deposits as sources of error. After a study of interfering elements was conducted, this new method of determination was ver­ ified by analyses of steel and nickel alloy samples, in which the time usually required for the separation of cobalt was shortened considerably.

In a study of the cathodlc deposition of metallic cobalt, the use of cobalt-60 and a solution counting tech­ nique furnished an easy means of analysis of the residual electrolyte and wash solutions. It was shown that cobalt losses occurred in each of ten of the generally used pro­ cedures, the amount varying from 0.01 to 4.0 mg. The co­ balt left In solution had been deposited, but was redis­ solved during the washing process. The formation of sur­ face compounds during the last part of electrolysis was shown not to be the source of positive errors. A quick soot nlate method was given for the estimation of residual

CODftjt.

1 5 8 159

A study of the rate of precipitation of cobalt by potassium nitrite was made under widely differing condi­ tions of volume, concentration of cobalt and reagent, temp­ erature, and the presence of other materials. The cobalt analyses were again performed by the solution counting pro­ cedure. Except under the condition of very low concentra­ tions, the precipitations were quantitative in less than the usually recommended 24 hours. A procedure was recommended for use in cobalt analysis which gave quantitative pre­ cipitation in two hours.

A study was made of the soluDility losses of cobalt durinr the double phosphate determination and the cooalti- nitrite senaration. The optimum pH range for precipitation of the double phosphate was 7.2 to 7.5.

The end point of the titration of cobalt with a solution of l-nitroso-2 -naphthol in 60% acetic acid was detected by radiometric means. A comparison of radiometric with conauctometric and amperoxnetrie methods was given.

The relative solubilities of the cobalt compounds of anthranillc acid and four of its derivatives snowed that three of the derivatives, the 5-bromo, the 5-iodo, and the methylene di- anthranilic acids j;ive cooalt com-

Dounas that are less soluble tnan the ant irir anil ate, and these reagents may prove of value in certain analytical determinations. appendix; I

Organic Irnvinetric and Colorimetric aeagents for Cobalt

Zxanples recent deferences aenarhs

j.itroso oo.r ounas:

1 -iiltrosc>2-.x.phtbol Ko.nar «Tolniachev, Zhur, Anal. Kiiin* Principally gravimetric 21(1950); iaulais .arhuenda. reap nits. Colorimetric Dull. soc. chi,. 1 ranee 206(1951); if extracted by organic hichol, Gan. J. Chen. ^1, 31+5(1953); solventg. In most cases hobuichi, J. y.e, . Doc. Jaoan. Pure the Co-11 cod, is formed C.:e Dcct. 413U955;/ first; excess re;.rent produces varying amounts 2 -iiitroso-i-rnpAx.o!L oaron, Z. anal. J en. 140. 173(195'' ' of the C o ^ cpd.; hence beyuet, iinalos asoc.

0 -rdtro necrose! Dilis ii.oi.jpson, ind. Dng. Ghe;;i., .uial. Zd. 17. 254(1945) •

1 soniirosodinetnyl- dCiio:.ie, Gurrent Dei. 15, 107(1946); dihydrore sore inol ■ ruial. Cidiii. ncta 679(1949) 3 -nitrososalic,.'lie ;aid Perry * Serfass, Anal. Chen. 22. 5o5(1950).

H 8 nsendix I cont’u or uinic Iravi:ictric ana Colorinetric .parents for Cobalt

ua. cries ..ecent Ee fere rices denari; s

i.' troso-h-salt (dC3) ioun- -t al., Ind. -a-". Clien., ioial. I.uS is the noct widely

(ci i sulfo aai ed 1 -1 d 11 -o so - 2 - ->i.. 13, .174(1946) used colorinetric re- :iu_ hthol) cvent- u-nitroso- -ixv'dtJiol-i-suI- . .hin, J. leu. vordoaux 12b 61(1953) i'onlc acid

1 -ni^rc ooci.ro. cotro 1c ncid Ui-riitroso ” 11

2 itroscphenol: vrd.aleiu h o r . e e dixrocheuie ver 1 dhrochiu. dor qualitative tests, - c i a ^ 31411950).

1 -nitroso-2-..a.)i»t..-s’il- 1-oiLlC ac. a ^ i ■ a 1— nit,. ■ o so - a- na c. __.ici.n-nc u:ac * Grracova, G^en. List;,*. 4 jL? ■iravi. letric reaqe: as. 2 -iiitroso-l-na;-tu la..iinea 367(1953).

ioi'iitroso-nalorfl "uuiidiue Jean, iUial, Cidr.1, ^c sa, N_. • *—97* i 2j 523(1952)

I sordino sotc.ioca.r ...or

uxiues

2 -i r.xiro;c:/-l-:iaLi V i. :.aldo:d_ue -.ntio * i-ashiiia, J. Chon. Soc, Japan, In audition to these, Pure Chen, doc. 2kj 564(1953) a larre nunber of o:d. les are qood for qualitative _l satin- -oxn.be l/O st s. /ippe;idix 1 cont'd ur ;xnic Gravimetric and Golorime brie iiea^ents for Jobalt

aoa.iDles .iecent deferences .ce:.iarics

Diiet ir.'lr* lvo :dme Lee* Dieid, froc. Iowa ucad. Dei. X u l-7UviO)

j 0 1 113 0 ^ C ii* 0 . uTL Li-C ^*-C d t l ..usaiite, laze, el.ini. iual. 73.536U v4d )

' uenanthraquinonc-

.. .„.:U

.a loLpGro:_Lc aciu *. ..uzicha, JLem. rist;: £7, 13YC(Iy$3) u.cio-ir.;e

-..j-oa maos:

i'.uueamc acxa

oxanilic acid i.doa due

o —diem'on. ixcio-1>.o.our.;a

.jic.nranilic .»cias:

:.0iae_u others are listed on pa:;e . Grief disad- i -bro:. iou*is: .rani lie .-icida vanba^e is insolubil- it;- of the reagents. * 3 ,5-ciijro;.ioa:it..ra.*lIic acid Jiatii S. Labadi, jcience J alt are Ld ;~4JU953;

-a.u.1 io—G- ■ ia - ■ • u*iio i-C etc — a D^. ■ ax. j ^ ulal* >*** :x. itosa 11 ^ a/ ^ 1) 162 Appendix I cont'd or-anic dravimetric and Colorimetric deagents for Cobalt

nxonples I.ecent deferences dei narks

Oxine a_.d derivatives . a oxine lentryt Sherrington, .analyst 17 Insolubility of reagents (1950); Serges, dev.aeau. cienc. exact, similar to ant iir ani lie 2-net ay 1 oxine fis.-quim. y na^. iaragosa Jj 107(1952) acids. Lorrel 3- Paris, Anal. Cidm. Acta 573 ,7-uibrono oxine U951); ibid 4 , 267(1950)

0ithiocarbamates

Dinine Pribil et al• t Cheft. Li sty 46. 603 Soi.te cobalt complexes d952) ..say be extracted vdth Oupral ibid. Coll. Czech. Che:.;. Co..-.mnica. organic solvents, e.g., id (195 3) cupral complex vdth J arba.iates of I-alissa ililier, Ilia roc hej.de ver ethyl acetate; permits bis( p-sulf oyiienyl) a dne .dk roc him. Acta 40, 63(1952); Chilton, Co-Id separation. Other indole Anal. Chen. 26, 940(1954). earba-.iates are good aniline qualitative reagents. di icthylglyoxine

Organic bases + JC*. hydrazine Typical salts are: (Ph/^As^Co (bCh)^ rvr.'.dine and (Ph3S)3Co(SCN)i,. dercury also forms a I, icotine Burkat et al., /dr. Anal. nhin. cobalt-thiocyanate 325(1951) double salt. 0 or amine Appendix I conl 'a Organic Cravi.ietric and Colorisietric dea~enco i'or Jo alt

■dXi'L.aiics necent deferences le::iarks

Ii ercL’ie bi Lylene tatra..ine

Triuethylphenylarsoniuri salts >.-;yer et al., J. Proc• itoy. doc, 1. b. ..ales 21> 113(1946)

S ILfoniu.i Conrounus Poriraz *r uosen, /nial. Chen 21^ 1276(1949)

a Her ..o'-‘-ents: a ravx.:c srac:

Phenyl hyuarooin mid. Jarrido, .•dales iis. y q :i;a !£, 1195 Juval suggest * that tPiohyuartoin U 947 J; ..ess, x.etailurqia 21> 97 UV 53) these reagents be used .ore extensively. Phenyl or sonic acids rortnov, Jiur. Cbsci.ci 4 him. 13. 594 o(Jl^ 1943) /vrsi.iilic acid ;.usii * 101/ ii j *.. anal. Jne:.i. m , 11(1954) ruinaluinic acid .^xjui.dar t be, J. Indian Che:.;. 00c. 3C, 123(1953)

aayhtiyl t-.iocroa Hatki * Kabadi, loc. cit.

iVciiiuilclIr6S

Co lori 'lebric:

b - b e nzy 11 i 1* u ro n 1. chloride bteiguann, J. doc. Cneu. Ind. 6^» 233(1946) ibid 66 . 353(1947) Appendix I con; 'a or.;ur_Lc Jraviaearic ani Joloriaebric Reagents i’or Jobalt

a>ca...r>±es itecent deferences be:narks

i^'draziiie carix>:\ lie acid Vo’elsanj, -ec. trav. cein. 749 (l%u) derivatives

Giro iotro ic blue LiuOl^. J.OC • Cxt.

oalicy aide H u e beer, laai'ocke.nie vcr. Mikrocaim. dielbvldii. ane .wC a j*LLi3, 11 (1117)

^zo ayes ill... <• Lucolu,Am. "11. y}.iY'L( -

iii.ti uToue ..oo::r_L:i H e 13, 337{lV47)

bitrilotric.ee die .:to lei ..ielzci: *- Lbltz, anal* Glen, 111, 32SMV54)

barbituric co..; o : . a ■Jean, loc, eit.

iarilari et rev, asoc. Hoyaiu. ar ■ entinc. 20, 173 v 175 5)

,L~. Li U77’iX<(a * baaerjee, bcience -urea l i t re 12* 573(1954)

iartrater bobtelsiry *r h'eitner, Bull. aoc. cliini. I ranee 774 v. 1 51)

icld e articular I/.- rood t.'ci-id:.- fcrad 165 appendix II

* rinci moI or-r_nic .xarents for Cobalt - a. Cravinetric

.. caveats .0. - .111:' . on IS .iC .Turks ..cccnt ..cferences

O 'llfioe 0 66-+ f-jO 3U Cr; otaliine prooipifai.es FI ascii: a, A. anal. Chen. i.i Ji ^ . i 'a .v lJj. . uay be obtained in uhe pres- 13.7. 107bt952); Maleeva, 01 iC c of • 1 ridine, bo. © qc- Jiur. Anal. thin. jS, 333 ; 10011 o . pt'n possible. (1951); Audnev, ibid, 3 3 v 195 3) .o.ospnace jOiti Ip-'U/,, O^jO dee olier v/ork on this loldstein, Chemist OC M'MOy nethod in this disserta­ ^..alyst /£, 42 ( 1954) tion. ' - r • • \ \ U Double tiiiocyauate 00 (if’ ) iny be extracted for color­ Lanure, Bull. soc. chin. imetric det'n or titrated 061(1946); Sierra and uith MIU^. Can mask Fe and Carceles, Anales. real hi vritii oxalic acid. soc. espan fis y quin. 47B. 2 7, 341(1951); Marlines, iUiales univ. Murcia, Curso 219(1950) u yamne n ~ 3uu^ - ^..;5r ’ ' a Precipitates difficult ixnadkevich et al., Zhur. ■+■ i.ui. to vaah. A nal • A hi;.. 123 (1946)

* cl hitrites 1360 (..Ci)6 3t;e Ci.. 3 for results of Mallnann, Anal. Ciicn. 22. rUvUU, *^*0^ i^cL-O^ uoi'3.Jo (^0^)6 an investigation of tils 1519(1950) '■_»0, j 0 d . ethod.

a. These vjeirhd:vr forms wore reco.i end u 0 juvai.

h> O) 0 1 ^npendix al cont'd principal inorganic descents for Goijalt - b. Golorii.ietric

i^eajent s Jolorod F o m deriarks decent References

F *iioc,.'anate Jo3JI.) 6 4 blue, I*ask Fe with ascorbic acid. kiimunen et al., Cherist Voxel's Reaction Extraction into organic sol- analyst 42» 21(1954) vents increases sensitivity. - Carboni, La Chi:a. e L* Industria, 50(1956) Ferri cyanide Go(Fe(Gi;)6) 6' 4

:ici Co(Cl)6"*

d ^0,2 + ivi lJO3 00(103)3 3 .,or Lay be used for indirect Laitinen fc Buraett, Anal. 100(003)3 ''.Green voluuetric deter::inations. Chela, 2^, 1265(1951)

li202 in a.Lionia oo(iiU3J& red-violet

^ fku-i-ios, i.auii Cc(QiiK(iLC) -2 Can detect 0.05 rig* Oo per Gordon Schreyer, Anal, rl, by tuis color. Gke:.i. 2£, 351(1951)

H 0> appendix III

VoliL.icoric hetuods for Cobalt

j-Vpe of Unci Point ..ecent i. -i-t ra ^ -LOn Aearents Used Detection References

;te aox, i no iucliHl; h3re(Ch)6 i-n i -3» Pot er.tione trie or Yarcliey, Analyst 21r ^5b titrations of fhis is the ..ost Polarimetric (1950): 'io::ii.cek et al., precipitates In -o roant vol. metric Coll, .izech, Cham, Conmnica. . ;0.... .od. lit. 20(1949) 5 Chepik, Zavod. Lab, 11, 1470(1949); Clanaurh et al., J, nes. t.nt’l 2ur. standards 73 (19 r>4); Lalvoaa *» Zyka, Chen. ixsty 462(1951) roJv^ + ^.pCr^C?

U cji.+

^ ~. a ^ *“jeU j

***- 3

+ -*hCC3 imperonetnc Durdetl and Laitinen, loc. cit. Pribil, Coll, Czech, Chem, Co. nunic. 1 ^ 31(1950) . +3 ■ JO

Jo..^le:5o,iLetric +JJ ±d\ Indicators Flasciica, i*i.rochin ver 1 JLkroCidjii Acta 30(1952) » T^l * *. I i. 1 i harris bweet, Anal, Chen,

26, 1649c1954)J Suartzonbach 168 iielv, Chin. ncta * 1,1*7(1111} Aimendix1 4- III coni'd Yolur.etric Lethods Tor Cobalt

i o oi rind Point iiecent i it ration uca 'onus ised betecLion aefcrences

.iriu.-l Potentionetric Javicuhi, jam. chin. L^ne) 40, I5J(1950)

aara-cs Conduetone trie iobteisk" 1c Sine he;', i-u' 1 • soc, ciii Prance '70(1950 )

'j’.'auue .d_uctroi.ietric Jochevauov, iavod. Lab. H u nd7av4d)

.iC idiue-ric xnuicnLorG Lurried * Perez, anales real soc, espan, i'is 7 quin, jo-j. lul(195b)j toetzeo, u, Soc. 997(1951) n on-a< iu'jouc - j_u ^ xri ^ j- o XjCu iG Potentionetric or rifcr *< dollish, Anal, visual Cue:.:, 24, 519(1952) rreciritatlon bead Stou Vl(193l); Fritzsche, iTennstoff-Cnaa, 49(1954) oxine Outside indicator Bucrerer * -Leier, 1. anal, Ciieu. 39, 161(1932)

01 <0 Appendix IV

Experimental Details

The Isotope Dilution Technique

The isotope dilution method of analysis was applied to the anodic deposition problem. A general discussion of this method may be found in the series of papers In Analyt­ ical Chemis t ry , Vol. 21, 1949, or In the survey and pro­ cedures of Plnajian, Christian and Wright.Recent uses of the method Include applications to penicillins analysis and to the determinstion of strontium In sea water.^®*^®

The present work involved the direct approach, i.e., it is based on the fact that the decrease In concentration of active isotope when an isotope dilution is made gives a measure of the amount of Inactive material originally pres­ ent. More specifically, the method as used here consists of the oreparatlon of a standard curve which is a straignt

line obeying the following equation:

w =H m )w - »

/i/here Is the weight of inactive material to be diluted by

w milligrams of active material to give a mixture having a

soeciiic activity of SA} (measured In counts oer minute per

milligram). SAq is the specific activity of the standard

tracer material.

A known volume of active cobalt solution (w mg. and

specific activity SAq) I 3 added to each of a number of sol­ 171 utions that contain k n o w n amounts of cobalt {W milligrams).

If some of this active isotope mixture from each solution

Is isolated in a pure, weighaole, and easily countable form, a straight line graph can be constructed in which

W is plotted against l/SA^. Then when the quantity W is unknown and the same volume of active cooalt solution Is used, the specific activity of the isolated portion allows one to find W from the standard curve.

In the present work cobalt was Isolated as a hydrated oxide. This was deoosited on a platinum disk which served as the anode In a modified tower electrolysis cell. Since beta ^articles are subject to appreciable self absorption in the deposit, only gamma radiation was counted; the beta was filtered out with an aluminum absorber.

Apparatus

a. Anodic Deposition btudy

The platinum disk anodes used for the deposition of

cobsltic oxide were lb/16" In diameter and 0 . 0 0 5 " thick, with one surface uniformly sand-Dlasted. These were ob­

tained for use with the Tracerlab planchet holders, shiel­

ded manual-samole-holder, No. 5C-9D, and electrolysis cell

No. E-1 6 as modified by Sweet and Theurer. ^ 0 A Tracerlab

T3C-2 GrM tube was used for counting the denosits, end a

Fotter predetermined decade scaler, Model 341 wa 3 used to

record the counts. 172

b. Liquid Counting

A liquid counting technique was used in the studies of the deposition of metallic cobalt, the cobaltinitrite method for cobalt, the radiometric titrations, and the sol­ ubility studies. Because of the very penetrating gamma ra­ diation of cooalt-60, direct measurements of the activity of C'-'oalt in solution are possible which are quite conven­ ient and time saving compared to the usual methods, e.g., evaporation to dryness in petri dishes. Disadvantages of liquid counting as compared to that with isolated dry sam­ ples include (1) the loss of sensitivity due to absorption of radiation in uhe solution, and t2) the fact that some isotopes contaminate glassware by being adsoroed on it.

The latter difficulty was not encountered with cobalt-60.

The liquid counter apparatus that was used was

Model LC1 of Nuclear Instrument, and Chemical Corporation,

Chicago. It consisted of a cigar-shaped Geiger-Miller counter tube (Nuclear*s D-52 or Tracerlab TIC-6), a cable for voltage suoply from scaler to counter, a jvarineili oeaker, and clamps for the beaker and counting tube. A

Marine.! li beaker has a glass tube sealed vertically tnrough its center so the counter may be surrounded by gamma emitting liquids without being wet by them. This apparatus is pic­ tured in Figure 11.

c. Other Apparatus

Other special apparatus that was used in the work fT3

''UN TE R PAHATU 174

Included an Eberoach rotating electrode electroanalyzer, a

Beckman Model H2 pH meter, a clinical type centrifuge and

50-ml. Pyrex centrifuge tubes. A large Cenco centrifuge,

"International Centrifuge No. 2 ” and 200-ml. centrifuge bottles were used in the radiometric titrations. The con­ stant temperature oath with agitation motor and spindle which was used in the solubility study was that of R. M.

Hall.145

As far as possible riExax" volumetric glassware was used. It was calibrated in the usual way. Radioactive solutions were pipetted by a remote plpettor when neces­ sary or b'r a "Propipettes" ball-valve, ruober-bulb safety pipet filler when small ssmoles were oeing transferred, standard active solutions were stored behind ieaa orick when not in use.

Counting Procedures

a. General Procedure

Counting was conducted a3 follows: Aith all con­ trols In the "off" position, the scaler was connected to the 110 v. outlet; the sample changer or liquid counter apparatus (Fig. 11), with the corresponding GM tuoes in position, was placed beside the scaler and the cable was attached to the high voltage supply of the scaler. The power was now turned on and advanced to the prooer oper­ ating voltage. (The operating voltage was determined

about once per month by clotting a volt-count plateau). 1 7 5

After a half hour warm up period, a blank (disk or Marinelli beaker with water) was placed in counting position, (with an aluminum absorber in place for disk counting), and a 30 min­ ute background count was taken and recorded. Then a stan­ dard sample was exchanged for the blank and counted for

40,000 counts and its activity was recorded.

Next, the sample to be measured wa3 placed in posi­ tion and counted for a suitable number of counts, e.g., if a relative statistical deviation of no more than 0.5# was desired, the count should be 40,000 or more since the rel­ ative deviation is given byjl^l

V n '

The observed activity of the sample was then calculated in counts oer minute and the coincidence, background, and efficiency corrections were applied, respectively, to oive the net activity.

Coincidence corrections were calculated from the usual equation*. 1 ST Correction s* - N0 = NrTlI 1 * 1____No J 'here N a is the actual activity, NQ the observed value ana

is the recovery time of the tube. For making these cor­ rections it was most convenient to make a dot of Na - NQ

vs. N0 and read the corrections from the graph.

Efficienc;/- corrections were based on the daily count

of a standard samole. If the standard xave x# more counts 176 on a given day than on the first date It was counted, then all counts taken that day were decreased by x£>. Hence, all samples could be compared on the same basis. This correc­ tion was necessary because of variations in the counter from day to day and because of any shift of the plateau of the Ciy tube. It could also be used to compare one GM tube with another If a replacement had to be made. The small correction for decay of cooalt-60 would also oe in­ cluded In the efficiency correction.

b. Liquid Counting

Using the standard radioactive cobalt solution pre­ pared for the electrolytic study (#1 p. 178), a series of solutions were made up each of which contained a known amount of cooalt In 100 ml. Each sample was olaced in the

Marinelli beaker and Its activity was measured. The ob­ served activities were corrected for background, and coin­ cidence, and a olot or net activity against weight of co- nalt taken was prepared--Figure 12. In the activity range that was used, ooserveo activity was directly proportional to the ouantity of cooalt. Tnis was true for ooth the

D-52 and T I C -6 tubes.

When It had been established that the liquid counter

gave linear resoonse, It was not necessary to ootain a new

standard curve for each standard active cobalt solution that was used. It was sufficient to determine the "solution

specific activity", I.e., the activity per mg. of cooalt as Activity in Counts / Minute 2400 2000 1600 1200 000 400 0 0.2 Response of the Liquid Counter Counter Liquid the of Response g f oat Taken Cobalt of Mg 04 i. 12 Pig. 06 0.8 1.0 177 178 measured In a volume of 100 ml. in the liquid counter.

This was done by using two or three samples prepared from the standard solution for which the "solution specific activity" was desired and calculating the average numoer of counts per minute per milligram. This is equivalent to the use of the slope of a curve constructed from two or three points. Values of the "solution specific activ­ ity" for each standard active solution used are J.isted below along with the standardization data.

Chemicals and Reagents

a. Cobalt

Solutions were prepared from spectrographically pure cobalt sponge of Johnson Iviatthey & Company, Ltd.,

London. They were standardized by titrating with ethylene- dlaminetetraacetic acid according to the procecure of

Harris and Sweet.1 ^ 2 ^ millicurie sample of high purity cooalt-50 was obtained from the Oak Ridge National laboratories and portions were used as needed.

Anodic Deposition Study

A standard coDalt solution consisted of 1.000 gram

of the sponge dissolved In the minimum amount of sulfuric

acid and diluted to one liter. The standard active tracer

solution contained approximately one millicurie of active

cooalt and 200 mg. of carrier in one iir,er. 179

Electrolytic Study

Solution # 1 . One and two tenths grams of sponge were dissolved in 5 ml. of sulfuric acid, one millicurie

of active cobalt was added and the solution was diluted

to 1 liter. Standardization by EDTA gave:

Volume taken, 25° C.: Cobalt found:

24.98 ml. 29.93 mg.

24.98 29.96

Av. 29.95 mg.

The solution specific activity was 205Q counts/min./mg.

with the D-52 tube and 1326 counts/r-in./mg. with the TGC-6.

Solution # 2 . Two and one-half grams of sponge were

dissolved in about ten ml. of sulfuric acid. One me. of

cobnlt-60 was added and the solution was diluted to 5

liters. Standardization:

Volume taken, 25° C.: Cobalt found:

24 .98 m l . 24 .55

24.98 24.55

24.98 24.54

Av. 24.55 mg.

The solution specific activity of ft2 was 1576 c./m./mg.

using the TIC-6 tube.

Solution # 4 . One gram of sponge was dissolved in

b ml. of sulfuric acid and diluted to one liter. This was

mixed well with 200 ml. of solution ftl • Fifty ml. of tnis

solution contained 51.6 mg. of cooalt; tnis solution wns 180 used in the rate study and not the studies where the depos­

its were weighed. The solution specific activity was 221

c./m./mg. as measured with the TGC-6 tube.

Gobaltinitrite Study

Solution //5. Two grains of cobalt sponge were dis­

solved in the minimum amount of sulfuric acid and diluted

to two liters. This solution was then mixed with 600 ml.

of solution jt2. Standardization:

Volume taken, 32° C.: Cobalt found:

24.98 ml. 24.62 mg.

24.98 24.69

24.98 24.77

Av. 24.70 mg.

With the TOC-6 tube 1 mg. gave I860 c./m., while with the

D-52 tube it gave 2075 c./m.

Radiometric Titrations

Solution yb. Two grams of cooalt sponge were dis­

solved in the minimum amount of sulfuric acid and diluted

to one liter. The carrier free active solution that was

used contained 2 me. of cobalt-60 in 1 liter of water.

De fLonick’s Reagent105

The radioactive solution of Na3Co(N0g)6 for the

rate study of the potassium determinations contained about

0.5 me. of cobaJt-SO plus the usual amounts of cooalt

nitrate and sodium nitrite, in 1 liter. 181

Solubility Studies

Solution jf6, This solution contained 500 ml. of solution #5 plus the remaining cobalt-60 in the Oak Ridge sample (about 0,3 me.), and it had a solution specific activity of 832 c./m./mg. as measured by the T0C-6 tube.

Solution #7. Five hundred ml. of the carrier free

active solution from the titration 3tuay was evaporated to 300 ml. To this was added 0.5000 gram of cooalt sponge that was dissolved in a little nitric acid, and the whole was diluted to 500 ml. The solution specific activity was

1780 c./m./mg. with the D-52 tube.

b. Other Chemicals and Reagents

Potassium Nitrite. I/ierck reagent grade, granular,

minimum assay 87/3. Titrations with potassium permanganate

showed this to be 94% potassium nitrite.

1-nitroso-2-naohthol. The solution used in the

radiometric titrations was approximately 0.1M and was

preoared using 60% acetic acid as solvent. The Eastman

reagent was used as received.

Anthranilic Acids. Anthranilic acid was oDtainea

from Coleman & Bell and was used as received. The N-phenyl,

the 3,5-diiodo, and the N-methyl derivatives were avail­

able as Eastman white label reagents. N,N* ethylene di-

anthranilic acid was obtained from W. F. Karri;!53 The

5-iodo, and 3-oromo-5-iodo derivatives were orepared and 182 purified by the procedures described by Romero.137 The

5-bromo and 3,5-dibromo acids were prepared by the method of Wheeler and Oates;153 they were recrystallized an ad­ ditional time. The hydrazo di-, bis ammonia di-, methyl­ ene di-, oropylene di- anthranilic acids and o-(aminomethyl) 14n benzoic acid were obtained from W. A. Young. 183

Appendix V

Counting Data Table 2

'.Vt. Deposits Total K f f . Back­ De ad Net Mg. C./M. C o r r . ground Time Activity

2 . 624(M ) 6273 72* 125 S326 0.732 807 43 2 767 0.435 508 56 451 0.526 576 52 1 525 3.17 4(M) 11732 51 475 12156 1.613 6203 51 150 6232 0.203 504 52 1 453 1.044 2001 55 13 1959 0.878 1754 55 11 1720 0.973 2037 52 14 1999 0.925 1925 52 12 1865 0.929 19 63 51 13 1925

Table 4, same columns, TG 0-3

2.312(M) 100 62 -2.33 fo 41 311 10332 1.672 4353 -2.0 45 67 4376 1 .755 4270 tt 45 47 4170 0.952 3216 0.0 41 16 2291 2.032 4976 -2.0 45 33 4915 1 .14 6 2852 0.0 47 32 2837 2.242 5251 if 47 95 5299 1 .431 3724 t> 47 50 3727 1.429 3305 tt 41 37 3301

Table 5, same cojunns, TG C-2

5545 0 48 141 543Q 52 34 tr II 140 5426 4308 ii II 113 4373 3815 H It 100 3867 3151 183 59* 36 3316 4 071 243 42 60 4331 2853 169 it 31 2991 6115 125 78" SO 5223 1347 10 6 96*"' 67 4442

These disks were contaminated by an ignition ana had

a high background count. 184 Counting Data cont’d

Table 6

wt. Total Dead Back­ Efflc. Net Deposits A. Time ground C o r r . Count

3.797 5203 95 46 436 5669 3.989 5568 110 43 379 6014 3 • 655 5092 90 46 426 5562 2 .052 3173 38 46 266 5430 1.952 2993 37 46 253 3255 1.931 2907 32 43 198 2094 Table 11

161 0.632 1090 5 50 2 1047 1680 1.340 2223 6 50 1 2180 1627 1 .460 2384 6 51 -91 2248 1540 0.511 1004 3 62 -83 862 1687 0.637 1222 4 62 -96 1068 1675 2.237 3479 7 66 0 34 20 1530 2.148 3372 7 66 0 3313 1541

125a0•624 1103 3 49 -79 978 1565 1.434 2406 G 49 -61 2302 1608 0.507 861 2 52 0 811 1600 2.069 3455 7 52 0 3410 1558 2.189 3445 7 52 0 3400 1551 0 . 635 1005 2 52 0 1005 1582

162 0.609 892 3 47 23 871 1430 0.727 1047 4 47 26 1030 1417 1.182 1669 5 50 0 1624 1373 0.766 1155 4 50 0 1109 1445 1 .534 2293 6 50 0 2249 14 65 1.141 1646 5 50 0 1601 1403

157 0.553 870 3 49 37 787 1422 0 . o 65 912 3 49 39 887 14 62 1.552 1039* 3 186 1334 2190 1385 0.692 -41* 1 186 557 913 1311

Counted with a TGC-8 tube, factor 2.062. 185 Counting Data cont'd

Table 9, TGC-2

Metal Weight Total Dead Back­ E f f . Net S.A. Deposit s A Time ground Corr. Res A

- 2.318 3516 45 52 16 -21 3505 1515 - 1.078 1713 10 52 8 - 4 1675 3 552 Pe 0.934 1499 7 52 8 1462 1565 Pe 0.712 1142 4 52 6 1100 1545 Cu 1.286 1947 12 47 62 1974 1535 Pe Cu 0.968 1525 8 48 37 -48 1480 1530 Fe Cu 0.510 804 2 47 7 766 1505 Cr 0.939 1447 7 47 57 -37 1428 1522 Zn 0.727 1114 4 48 34 1104 1520 Bi 1.031 1595 9 47 51 -48 1599 1549 Ag 1.489 2238 16 48 39 2258 1480 Al 0.440 720 2 47 6 681 1527 Ba etc,. 1.154 1694 9 43 91 -48 1704 1521 Pb 1.127 1666 9 43 89 1721 1527 Cd 0.600 1010 3 51 -12 -37 913 1521 Ni 0.842 1203 5 48 8 it 1131 1392 Ni 0.785 1178 4 48 7 -21 1130 1442 Nia 0.719 1074 4 47 9 1039 1448 iua 1.167 1625 8 52 8 1593 1390 Mn 1.903 340 1 48 2 295 155 As 0.900 94 6 3 52 5 902 1002 H r 3.324 4133 60 49 316 -21 4439 1340 Hg 0.420 39 6* - 200 223 476 1135 Mn sep . 0.389 15 61* - 213 - 1349 1518 Mn " 1 .602 2579* 8 227 2452 1530 Hg " 0.762 1300* 0 187 - 1124 1479

■m- These samoles were counted with a TOC-6 tube while all

others were counted with a TGC-2. The Efficiency correction

is included with the total count.

cont’d next page 186

Counting Data cont'd Tabla 13

Expt Residual Co 3ol*n B a c k ­ Dead Net Mg. of No. Activity No. ground Time A Cobalt

1 2355 1 63 7 2299 1.12 82 1 68 14 0.01 2607 1 74 8 2541 1.24 76 1 62 14 0.01 2 778 1 68 710 0.35 161 1 68 93 0.05 72 1 62 10 0.01 1210 2 62 1148 0.68 3 96 1 72 25 0.01 224 1 72 152 0.07 160 1 41 119 0.06 iei 1 62 119 0.07 4 1380 1 52 1328 0.65 8255 1 50 80 8285 4.03 4530 2 52 25 4505 1.64 4550 2 52 25 4525 1.66 5 413 1 68 345 0.18 654 1 72 482 0.24 355 1 72 282 0.14 1210 2 62 1148 0.68 6 602 1 41 561 0.27 144 1 41 103 0.05 365 1 47 318 0.16 166 2 47 119 0.07 7 154 1 50 104 0.04 635 2 52 583 0.21 1233 2 52 1181 0.43 453 2 50 4 03 0.15 155 2 55 100 U.04 8 952 + 820 1 37 1755 1.31 4 69 ■+ 450 1 37 882 0.66 169 + 521 2 37 653 0.40 692 + 643 1 47 1288 0.97 9 577 1 36 541 0.27 141 2 55 86 0.05 457 2 55 402 0.24 2380 2 47 7 2540 1.40 10 94 1 61 33 0 .02 164 1 61 103 0.05 124 2 38 88 0.04 330 2 33 292 0.17 92 2 50 42 0.02 107 2 50 S7 0.02 107

Counting Data cont'd

Table 15

Time Net Activity and Time of Electrolysis M i n . E x o11 N o s .: 1 2 3 4 5 6 7 8 9 10 0 3919 34 66 3488 3559 3730 3600 3450 3860 3710 4012

5 181 791 391 1426 746 270 409 239 3710 2120

10 125 159 31 100 93 57 45 21 5230 829

15 57 0 0 6 0 10 9 27 2282 224

20 0 4 - 0 4 20 1485 81

25 - 0 23 7 704 29

30 - 15 7 311 7

45 0 14 6

60 - 3 -

Table 19

E x o 't Co vvt. Cobalt left Total No. Taken Deposits in Sol'n, Mg. Co Mr . Mg. N et A." Pound, Mg.

1 49.60 50.40 65 0.088 50.49

2 it 50.79 59 0.079 50.87

3 11 35.75 10668 14.35 50.10

4 1! 41.06 7123 9.64 50.64

5 11 38.88 3179 10.95 49.33

6 11 40.45 7667 10.28 50.73

7 ft 30.36 7680 20.65 51.01

Q n 46.37 3638 4 .88 51.25

* The 5.S.A. of the cobalt solution was 744.3 C./M./Mg. 188

Counting Data cont ' d

Table 21, typical data » Total Time Vol. of Total B a c k ­ Met % Co Volume in Filtrate Count ground Count in Sol'n V Ml . Hours Taken A a v Ml. C./M. C./M. c ./m .

50 0.5 10 66 58 8 0.1 50 0.5 10 58 58 0 0 100 0.5 50 59 58 1 0.0 200 0.5 50 52 43 9 0.1 200 1 50 47 43 4 0.0 225 2 10 78 51 27 1.4 250 24 25 100 30 70 1.4 e t c .

Table 22, typical data, V was 300 m l •, Sol' n #4, S.S.A. 221

T e m p . Time V Total Count B a c k ­ % Co °c. Hours ground Afi in Sol'n

20° 1 25 m l . 110 29 81 17.7 20 8 11 29 27 2 0.4 35 18 it 83 28 55 3.5 50 4 11 137 27 110 24.4

Table 23, V was 100 ml. , Sol' n #4, similar date for 24 & 25

■7t. Co Time V Total Count Bkgrnd A a % Co Grams Hour s m] . in Sol'n

1.025 0.5 25 333 29 304 2.6 1.525 rt tt 660 30 630 6.0 et c.

Table 26, same columns,

Mixture 7-1 1 hr. 50 ml. 31 26 5 0.08 etc.

The data for Taoles 27 and 28 were similar. bibliography

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153. A.S. Wheeler and W.p. Oates, J. Am. Chem. Soc. 32, 770(1910). AUTOBIOGRAPHY

I, Darnell Salyer, was born In Johnson County,

Kentucky, November IS, 1930. I received my secondary

school education in the public schools of Floyd County,

Kentucky. My undergraduate training consisted of one year at Pikeville Junior College, Pikeville, Kentucky,

and three years at Eastern Kentucky State College,

Richmond, Kentucky. From the latter, I received the de­

gree Bachelor of Science in 1952* From October, 1952,

until June, 1954, while doing graduate work in the Depart­

ment of Chemistry of the Ohio State University, I was a

teaching assistant in general chemistry. During the

school years 1954-55 and 1955-56 I held two fellowships

in the Chemistry Department. The first was sponsored

by the Cincinnati Chemical Works, and the latter by the

Central Division of the Allied Chemical and Dye Corpor­

ation. .Yhlle holding the position of fellow, I completed

the requirements for the degree Doctor of ihilosoohy.

197