I. WAR RF.SEA.BCH - AN INVESTIGATION OF SOME CHmMICAL

WARFARE REAGm'lS.

and

II. .AN INVmTIGA.TION OF THE PBlSICAL PROPERTIES OF A

TWO - OOMPONENT Sm'l.".D1 IN THE CRITICAL Tl!2J1PERATURI,

CRITICAL PRESSURE REGION.

A Thesis

by

w. G. Schneider, M. Sc.

Submitted to the Faculty ot Graduate Stud1es and

Research ot McGill Un!versity in pan1al tu.lt1l.ment ot the requirements tor the degree of Doctor of

Philosophy.

April, 1941. I wish to express my sincere appreciation and groatitude 'to Dr. O. Maass tor his continued interest and :many helptul. suggestions during the course of this work; his enthuaiaam was a cOD,at8Jlt source at encouragement.

I am indebud to Dr. S. Naldrett tor his collaboration in the experimental work with cy8D.ogeD. fluoride, to Dr. j. Dacey 8D.d Mr. A. Topp tor 'Sheir investigation at the method at preparation at phosphorus tritluoride and calcium arsenide, and to

Dr. S. Naldrett, Dr. R. Harvey 8D.d Mr. Ae Topp tor their oo-operatlon in the measurement ot the service times ot respirator charcoal.

Grateful ackllowledgement 1s made to the

National Research Council ot Oanada tor the award ot a Studentah1p and a Fellowship. TABLE OF CONTm'lB

PART I. - WAR RESEARCH. An Investigation of some Chemical Wartare Reagents.

A. 'Ihe Preparation and Properties ot Cyanogen Fluoride.

I. Introduction ••••••••••••••••••••••••••••••••••••••••••••• 1 II. Apparatus •••••••••••••••••••••••••••••••••••••••••••••••• 1 III. EXperimental...... 2 a) Preparation ot cyanogen tluor1de ••••••••••••••••••••• 2

1) Preparation ot cyanogen 10dide ••••••••••••••••••• 3

2) Preparation ot silver tluoride ••••••••••••••••••• 3

3) Jrocedure tor the preparation ot cyanogen tluoride...... 4

4) Preparation ot cyanogen tluoride trom cyanogen bromide ••••••••••••••••••• 4

b) Purification ot cyanogen tluoride •••••••••••••••••••• 5

c) Properties ot cyanogen tluoride •••••••••••••••••••••• 6 1) Physical properties •••••••••••••••••••••••••••••• 6

2) Results ot solubility measurements ••••••••••••••• 6 3) Chemical properties of cyanogen tluoride ••••••••• 10

d) Chemical test tor detecting cyanogen tluoride •••••••• 12

e) ~x1c1ty ot cyanogen tluor1de •••••••••••••••••••••••• 14

IV. Discussion ••••••••••••••••••••••••••••••••••••••••••••••• lfi

B. Meyurements ot the Service Time ot Respirator Charcoals tor

Poison Gesee.

I. Introduction ••••••••••••••••••••••••••••••••••••••••••••• 17

. II. Apparatus •••••••••••••••••••••••••••••••••••••••••••••••• 18 TABLE OF CONTENTS (cont'd)

III. Exper~tal ••••••••••••••••••••••••••••••••••••••••••••• 22

a) General procedure ••••••••••••••••••••••••••••••••••• 22 b) Charcoal samples used ••••••••••••••••••••••••••••••• 24

c) Experiments with arsine ••••••••••••••••••••••••••••• 25

1) Preparation ot arsine •••••••••••••••••••••••••• 25

2) Results ot service time DlBasurements ••••••••••• 26 d) Experiments with phosphorus tritluoride ••••••••••••• 31 1) Preparatton of phosphorus trifluoride •••••••••• 31

2} Results ot service time measurements ••••••••••• 33 e} Experiments with phosgene ••••••••••••••••••••••••••• 40

1) Construction of a.ma.ll service time apparatus ••• 40 2) Results of comparison measurements with phos88ne ••••••••••••••• 40

t) Experiments with cyanogen fluoride •••••••••••••••••• 44

1) Preparation ot cyanogen fluoride ••••••••••••••• 44

2) Test for detection ot cyanogen fluoride •••••••• 44

3) Results of service time measurements ••••••••••• 45

IV. General Conclusions •••••••••••••••••••••••••••••••••••••• 4'1 Bibliography ••••••••••••••••••••••••••••••••••••••••••••• 48

PART II•

.An Investigation ot the Physical Properties ot a Two - Component System in the Critical Temperature. Critical Pressure Region. I. Historical Introduction ••••••••••••••••••••••••••••••••• 1

II. Purpose ot the Investigation •••••••••••••••••••••••••••• 13 III. General Introduction •••••••••••••••••••••••••••••••••••• 14 TABLE OF CONTENTS (cant'd)

IV. EXper~ental •••••••••••••••••••••••••••••••••••••••••••• 16

a) Apparatus ••••••••••••••••••••••••••••••••••••••••••• 16

1) Description ot equilibrium bomb •••••••••••••••• 16 2} The thermostat ••••••••••••••••••••••••••••••••• 18

3) Analytical apparatus ••••••••••••••••••••••••••• 19

b) Materials ...... " ...... 20 c) Procedure ...... " ...... 20

1) Preparation tor an experiment •••••••••••••••••• 20

2) Filling the equilibrium bomb ••••••••••••••••••• 20

3) Sampling ...... " .. " " " .... " ...... 21

4) Analysis ot the swnples •••••••••••••••••••••••• 22 d) Results •••••••••••••••••••••••••••••••••.••••••••••• 23

1) Critical temperature and oritical dens!ty ot a 1:1 ethylene - propylene mixture •••••••••••• 23

2) Results ot phase equilibria measurements without stirring of the system ••••••••••••••• 28

3) Results of phase equilibria measurements with stirring ot the system •••••••••••••••••• 29

V. Discussion ot results ••••••••••••••••••••••••••••••••••• 32

S\lIIIlla.ry' ...... 37

Bibliography •••••••••••••••••••••••••••••••••••••••••••• 38

Olaims to or1ginal work •••••••••••••••••••••••••••.••••• 42 THESIS ABSTRACT

Ph.D. Chemistry. William George Schneider

I. War Research - An Investigation of Some Chemical Warfare

Reagents.

II. An Investigation of the Physical Properties of a TW'o­

Component System in the Critical Temperature, Critical

Pressure Region.

Cyanogen fluoride was prepared and its chemical properties

were determined, and its aolubility, toxicity and service time were measured. '.lhe reaults indicated that the gas is not particularly suited as a war gas.

'!he service times for arsine. phosgene and phosphorous trifluoride were determined for a number of respirator aharcoal samples by means of an apparatus which approximated the behavior of the human lung. All the impregnated charcoal samples submitted were shown to provi4e fairly adequate protection against the gases studied.

An intensive study of the phase equilibria of the two­ component system ethylene--propylene has been made in the cr1t1cal temperature region. It was shown that when the med1um 1s stined no discontinu1ty in density or phase composition occurs at the critical temperature, while without stirring the attainment of equilibrium is slow and uncertain. (PART I.

WAR RESEARCH

AN INVESTIGATION OF SOME CHD4ICAL WARFARE REAGENTS.

A. '!he Preparation and Properties at Iyanogan

Fluoride. (C.E••5).

B. Measurement. ot the Servioe T1ae ot Respirator

Charcoals tor Poison Gases. (C.E. 4). -1"

PART I : I A. THE PREPARATION AND PROPERTIES OF CYANOGEN FIDORIDE (C.E.25)

I. INTRODUCTION This investigation was undertaken to determine the adaptability of oyanogen fluoride as a war gas, and seoondly to determine whether the Regulation Army Canister provides adequate proteotion against it. To this end, oyanogen fluoride was prepared, and its properties were studied. Since a "light" war gas might be used to greater advantage when dissolved in a suitable solvent, it was neo­ essary to measure the solubility of cyanogen fluoride in a number of solvents. Finally, the toxioity as well as the absorption of cyanogen fluoride by respirator charooal was investigated. Cyanogen fluoride has been prepared by Cosslet (1) in 1931, and s~e of its properties were reoorded. White and Goodeve (2) measured the absorption speotrum of cyanogen fluoride. Apart from these two reports, little is known of the substanoe.

II. APPARATUS Fig. 1 gives a diagramatio sketch of the apparatus employed. It oonsists of a reaotion chamber, whioh is sur­ rounded by a tubular furnaoe F, and which has a oondensing 7. If, ••t

• . .. . J f s F

2 . bulb, D and E, at either end. The reaction chamber is conneoted to a manifold to which are also joined three storage volumes through stopcooks 4, 5 and e, two condens·

ing bulbs at 0, a closed-end manometer ~ the burette L, and the solubility oell S with a manometer M2' A liquid air trap B protects the oil pump trom oorrosive gases. The re­ aotion tube was about eo am. in length and 4.2 om. in dia­ meter, and could be dismantled from the apparatus by means of a ground joint at one end. The trap F (whioh is shown in

detail in Fig. 2) was used for purifying the ges. The solubility oell S wes also removable by meens of a ground jOint, and wes fitted with an eleotromagnetio stirrer H. The open-end manometer X2 was joined to a meroury reservoir, so that the total volume ot the solubility oell oould be maintained constant with changing pressures.

III. EXPERIMENTAL (a) Preparation of Cyanogen Fluoride Cyanogen fluoride was prepared as reported by Oosslet (1) by the action of cyanogen iodide on silver fluoride, as represented by the equation: ONI + AgF -t AgI + CNF Cyanogen iodide and silver fluoride were prepared as follows: -3'"

(1) Preparation of Cyanogen Iodide: Cyanogen iodide was prepared from iodine and sodium cyanide. according to the equation:

Is + NaCN --. NaI + CNI 24 grams of iodine were placed in a 500 co. round botton, three-neck flask and 40 ccs. of water were added. With con­ stant stirring a 5% solution of sodium cyanide was gradually added from a dropping funnel, until the iodine was oompletely disoharged tran the solution. Cyanogen iodide is but slightly soluble in cold water ,and precipitates as a white crystalline solid. To recover the remaining iodine, now in the form ot sodium iodide, a slow stream of chlorine was passed into the solution and sodium oyanide again added as betore. At the end of the reaction a slight excess of sodium iodide was added. The contents of the flask were then transterred to a separatory funnel and the produot was extraoted with ether. The extraot was then dried over oaloium ohloride, evaporated in a draught of air, and stored in a desiccator. The yield was about 70%. (2) The Preparation ot silver Fluoride: Silver fluoride was prepared by treating silver car­ bonate with hydrofluorio acid in a platinum dish. The silver carbonate was prepared by preoipitation from a dilute solu~on of silver nitrate by means of sodium carbonate. After deoompos­ ing the carbonate with hydrofluoric aCid, the solution was evaporated to 5 ccs on a sand bath, filtered, and finally evaporated over cone. sulfuriC aoid in vacuo, and proteoted -4­ from light during storage. The yield was about 64%. (3) Prooedure for the Preparation of Oyanogen Fluoride: Twenty grams of powdered cyanogen iodide were placed in the bulb D (Fig.l), while the silver fluoride (25 gms.) was spread along most of the length of the reaction tube. The reaction vessel was then joined to the apparatus, heated to 220·C. and evaouated. The bulb E was surrounded with Ii qui d air, while D was tmmersed in a glycerol bath at a temperature of 105°C to 125°0. This oaused the oyanogen iodide in D to sublime, pass over the hot fluoride and condense in E. The furnaoe pressure could be followed by the manometer Ml. The reaotion was found to be rather slow, which cculd be attributed ohiefly to the slow rate of sublimation of the oyanogen iodide. Subjeoting the latter to too high a tempera1ure would oause it to deoompose. Furthermore it was found that if the reaotion period allowed was too long, an appreciable amount of silioon­ tetrafluoride was formed. The best results were obta~ed with a reaotion period of eight hours, although in this ttme only about two thirds of the cyanogen iodide had sublimed. Under these conditions the yield obtained, estimated on the amount of cyanogen iodide aotually sublimed, was ~bout 25% to 30%. (4) Preparation of Cyanogen Fluoride fram Cyanogen Bromide: In the latter part of this wor~ cyanogen bromide was substituted for cyanogen iodide in the preparation desoribed above. This change was found advantageous since the bromide sublimes more easily than cyanogen iodide. The yield was somewhat improved and the reaotion time lessened by several hours. The oyanogen bromide used was either a oommeroial

produot of the Eas~1an Co., or, a produot prepared tmmediately before use from bromine and sodium oyanide by a method similar to that used for the preparation of oyanogen iodide. (b) Purifioation of Cyanosen Fluoride: During the oourse of the reaction, the oyanogen fluoride formed together with same cyanogen iodide condensed in bulb E (Fig.l). Bulb E was then Umnersed in dry-ioe-acetone mixture, oausing the oyanogen fluoride to evaporate through stopcook No.3 into storage volume No.4. This preliminary evaporation separates the product from oyanogen iodide and any water or hydrofluorio acid impurities. This was possible since cyanogen fluoride sublimes at about -?OoC. Any silicon tetra­ fluoride present will also sublime since its sublimation pOint is between -?OoC. to -900 C. The product was then condensed in bulb o. The final stage of the purification consisted in paSSing the gas through trap F to deoompose the silicon tetra­ fluoride. Trap F is shown in detail in Fig. 2. The inlet tube extends below the surface of several oubic centimetres of meroury to prevent the water from backing up the tube. On bubbling through the water silioon tetrafluoride is deoomposed

according to the equation:

3 SiF~ + 4 H20 ~ -6­

The amount of hydrated silica precipitated gives an indica­ tion of the amount of the tetrafluoride present in the product. The gas is slowly bubbled through the trap by bleeding it through stopcock No.1 (Fig.l) and condensing in bulb E. The purification is repeated until no more silica appears when fresh water is plaoed in the trap. The final product is again sublbned from dry-ice-acetone mixture to remove any water present. (0) Properties of Cyanogen Fluoride (1) Physical Properties Cyanogen fluoride is a colorless gas which readily condenses in liquid air to form a whi te solid. It sublimes at about -70°C., and could not be obtained in a liqu id state. By determining the vapor density, the molecular weight was computed to be 44.0. The theoretical molecular Weight of cyanogen fluoride is 45.00. This sufficiently identifies the gas for the present purpose. (2) Results of Solubility Measurements: In determining the solubility of the gas, a measured amount of solvent was introduced into the solubility cell S (Fig.l) and frozen with liquid air. The cell was then evacuated, after which the solvent was allowed to warm up by surrounding the cell with a water bath or an ice bath. The vapor pressure of the solvent could then be read on mano.meter M2. By means of the burette L, a measured amount of gas was introduced. The solvent YfaS then stirred by means of the electromagnetic stirrer H, and the change in pressure observed. The volume of the system, which had been previously determined could be kept constant by means of a levelling bulb attached to the manometer M2' Stirring was continued until the pressure remained constant over a period of twenty minutes.

A number of solvents were tested, and the results of these experiments are summarized in Table I. The last column represents the solubility (for purposes of comparison) calculated by Henry's Law (Pl = kXl), to a pressure of one atmosphere of oyanogen fluoride above the solution. TABLE I Solubility of Cyanogen Fluoride

Temp. °C. Solvent Press.of CNF Solubility %Solubility at equilibrium Weight Calculated per cent of cmr for 1 atm. pressure

Water 219 Mm. 0.08 .19 Ethanol 402 It 0.27 .51 Ether 359 n 1.20 2.50 Skelly Solve B 476 " 0.47 .76 Phosphorus Pentachloride 416" 0.20 .37 Hydrogen Peroxide (30%) 560 " 0.24 .33 20° Nitric Acid (1:1) 500 n 0.26 .40 20° Aniline 200 " 0.05 .12 19° Turpentine 353 " 0.32 .64 20° Lactic ACid 610 tf 0.15 .19 0° Propylamine 250 n (reaction forming whl te solid) 20° Benzy1emine 350 It 0.05 .12 20° Almnonia water 64 n reacts 20° Ammonium sulfide 62 " Potassium hydroxide {10%)223 " 0.49 1.45 -8­

These experiments indic ate that cyanogen fIno ride is difficultly soluble in all the ordinary solvents. In the oase of primary aliphati c amines a reaction occurs, probably an addition reaotion, to form a white solid. Acids, alkali and oxidizing agents were included in the above experiments in order to observe the chemical behavior of the gas toward these reagents. According to Raoult's Law, the solubility of a gas can be expressed in terms of its mol fraction in the soluticn as follows:

where Nl is the mol fraction of the gas in solution, Pi is the pressure of the gas above the solution, and pi represents the vapor pressure of the pure solute, or the saturation pressure of the solute. If Plo is known for the temperature under consideration, the solubility of the gas can be calcu­ lated for any desired pressure. If the temperatura in question o is below the critical temperature Pl oan be obtained from Tables or else can be measured. But if' the gas is above its critical temperature, as for example methane at room tempera­

ture, p! ceases to have any meaning as a saturation pressure.

However, by employing the method of Hildebrand (:3), a fioti­ tious value of pl oan be obtained by extrapolating the vapor pressure of the solute above the oritical tamperature, and this value of Plo can be uKed for an approxtnate oaloulation -9­

of the solubility of the gas. The extrapolation oan be made more oonveniently by plotting log pi against lIT, whioh aooording to the ClausiuswOlapeyron equation should give a nearly linear plot. From the extrapolated plot the value o of PI for a temperature of, say 0°0, which is above the oritioal temperature, can be obtained, and by substituting in the above squat ion, the solubility oan be oaloulated. The vapor pressure of oyanogen fluoride has been measured by Cosslett (1) from -139 to -70°C. By plotting these values and extrapolating, a value of 38 atmospheres 1 was obtained for Po for a temperature of O·C. If the gas pressure is one atmosphere, we have Nl - i} = 3\ = 0.0263.

This represents the approx~ate solubility of oyanogen fluoride in any solvent when the pressure is one atmosphere. In Table II, the solubility oaloulated in this way, and oon­ verted to weight peroent units for several solvents, is com­ pared with the measured solubllity. TABLE II

Comparison of Measured and Caloulated Solubilities of Cyanogen Fluoride.

Solvent Temperature SolubllitI (Press.: 1 atm.) Experimental Caloulated

Water 0.19%. 3.l~ Ethanol 0.51% 2.6~ Ether 2.50% 0.8~ Phosphorous pentaohlori de 0.37% O.91~ -10­

The experimental and calculated results are in poor agreement, but they are of the right order of magnitude, which for the present purpose is a sufficient test. The reader will be aware that beoause of the nature of this in­ vestigation, it was desirable to obtain practical results as quickly as possible. To this end experimental refinement had to be saorificed, and the solubility measurements must be considered as an approxhnation only_ However, the theor­ etical solubility values calculated in Table II corroborate the order of magnitude of the measured solubility of cyanogen fluoride. (3) Ohemical Properties of Cyanogen Fluoride: An attempt was made to study some of the chemical reactions of cyanogen fluoride with a view to obtaining a

chemical test, which could be adapt~d for use in the measure­ ment of the service time of respirator charcoal. The reaction with amines mentioned above was found to take place very readily with ammonia and primary aliphatic ronines, and somewhat less readily with secondary amiIBS. Iso-amyl amine also reacted very readily. But no reaotion was observed with aniline or benzylamine. However, phenyl­ hydrazine reacts similarly to the primary aliphatic amiDas. Acids and alkali were found to be without action on cyanogen fluoride. Even perchloric acid showed no apparent reaction. All the common oxidizing agents were without effect. -11­

In the products of the reaction with amines, tests for fluoride or cyanide ions were negative, and as it had been impossible to obtain these constituents in ionio fonn with acids, alkali or ozidizing agents, a number of reagents were tested which might be expected to give a color reaction. These included silver nitrate, potassium iodide - starch paper, tumerio paper, oopper rumnonium sulfate, oopper propylamine aoetate, potassium ferrioyanide, methylene blue, fluoresoein, mercuroohrome, malachite green, amine H acid, Congo red, rosaniline blue. No reaction was observed with any of these reagents. Although no study was made of the stability of CNF, several observations were made during the course of this work which may give some indioation of its behavior on storing. During the course of the present work the gas was stored in light insulated bulbs. When the gas was very pure, there was apparently no deoomposition during an interval of several weeks, but occasionally on condensing the gas and resubl~ingJ a less volatile residue remained. This pheno­ menon was again met with in the experiments on service times (see later), and although it was not investigated, it is probable that polymerization had occured. In another instanoe 400 ccs. of pure gas was plaoed in a light-insulated flask oontaini~ a little meroury. The flask was then inverted so that the gas would not be in contact -12­ with the stopcock grease. (Cyanogen fluoride does not attack mercury.) After 55 days the flask was opened. There had been no apparent decomposition or alteration of the gas. In another experiment some cyanogen fluorine was placed in a flask attached to a manometer, to observe the stability of the gas when not light-insulated. Atter 4 weeks no change in pressure was observed. (d) ! Chamical Test for Detecting Cyanogen Fluoride Since cyanogen fluoride is apparently quite un­ reactive, attempts were made to decompose it thermally and test for the decomposition products. These experiments may be summar ized as follows t accordi ng to the method of themal decomposition employed: (1) Beilstein Flame Test - A cyanogen fluori de- air mixture (concentration approx. 1:10) was passed through a small flame which impinged on a copper spiral. With halogen compounds a green coloration is produc ed in the fl arne • With cyanogen tltlOride, although a green coloration was produoed, the test was not sufficiently sensitive. (2) A number of tests were performed in which cyanogen fluoride - air mixtures (Cone. 1:10) were passed over a platinum spiral maintained at a white heat. The effluent gases were tested with potassium iodide - starch paper, d~ethylamino benzaldehyde - diphenylamine paper (4), tumerio paper, benz1dene acetate paper, iodine - starch paper, -13­

silver nitrate and ammoniaoal silver nitrate papers. The dimethylamino benzaldehyde - diphenylamine paper gave a positive reaction, but was not sufficiently sensitive for smaller concentrations of cyanogen fluoride. Cyanogen iodide, which in these experiments was frequently present as an im­ purity since it was deposited on the walls of the apparatus, also responded to this test. (In later experiments the test­ iIJg apparatus was joined to a new assembly consisting of a gas burette and a mixing flask connected with a manometer. With this apparatus, a gas -air mixture of known conoentration coul d be prepared and fed into the testing apparatus at any desired rate. The cyanogen fluoride was carefully purified before being introduced into this apparatus.) Several of the test papers mentioned above gave a positive color reaction, but these also reacted positively with air alone after it had been passed over the hot platinum spiral. Another test paper which was tried in this connection and which at first showed promise was the Schenbein-Pagenstecher (5) test paper (prepared by impregnating with dilute CU804 solution and alcoholic guaicol, and moistening with formaldehyde before use.) With cyanogen fluoride and cyanogen fluoride air mixtures, after traversing the 1:10 t spiral, a blue coloration of the test paper was observed. This test however was not sufficiently sensitive. Moreover the blue coloration was frequently very faint, and a slight positive reaction was obtained with air alone. -14­

(3) A series of experliuents were oarried out in which gas-air mixtures were passed through a heated silioa tube, and the effluent gases tested as above. Dimethylamine benzaldehyde-diphenylamine paper gave a faint test. It was found that the sensitivity of this test was greatly enhanoed when the silioa tube was packed with copper oxide and the

0 tube heated to a red heat (600 - 700°0.). Other catalysts e.g. hopoalite, silver, niokel and niokel oxide were not as effeotive as copper oxide. The Schenbein~Pagenstecher test paper also reaoted positively under these conditions, but presented the same difficulties as in the above experiments. The dtmethylamino benzaldehyde-diphenylamine was found more satisfaotory, and was used in measuring the service time of aotivated charcoal for cyanogen fluoride. The sensitivity of the test is disoussed in Section B. (e) The Toxicity of Cyanogen Fluoride Some physiological properties of cyanogen fluoride were determined. Two mice were exposed to a concentration of the gas of 1:200. Their eyes overflowed with tears immed­ iately, indicating the gas to be a powerful lachrymator, a property which is also common to all the cyanogen halides. One mouse was dead in 20 minutes. Further tests were carried out by Dr. R. Noble and co-workers of the Physiology Department. With a concentration of 1:1000 some rats lived for 48 hours. AutopSies showed d~age to the liver and kidneys. A concentration of 1:10,000 was not at all toxio. -15­

A study was also made by Dr. R. D. Gibbs of the Department of Botany of the effeot of oyanogen fluoride on oertain plants and seedlings. The gas was, however, found to cause no specific damage to the plant cells. (t) Absorption of Cyanogan Fluoride by Resnirator Charcoal. See Seotion B.

IV. DISCUSSION. The results of this investigation may be briefly commented upon as follows: 1. Cycnogen fluoride when prepared from silver fluoride and oyanogen bromide or iodide, is obtained in poor yields and is generally contaminated with silioon tetra­ fluoride if a glass apparatus is used. Because the silver is difficult to recover and beoause of the small yield the pre­ paration is an expensive one and not oommercially adaptable. 2. The gas condenses into a white solid which sub­ limes at about -70°C. A less volatile residue, which is probably a polymer,was frequently observed when the gas sub­ limed. The gas, however, is quite stable when stored in con­ tact with light or over mercury. 3. Cyanogen fluoride is difficultly soluble in all the common solvents. It reacts readily with ammonia and the s simple amines to form a whj.te solid, but otherwi se is chemic­ ally quite inert. 4. A test was developed by means of which cyanogen fluoride could be deteoted in an air stream. Using this test, -16­ the absorption effioienoy of the gas by respirator oharooal, that is, its "service time", was measured (See Seotion B.) 5. The gas is not extremely toxio. Beoause of its relatively low toxioity, diffioulty of preparation and insolubility and in addition as it is a relatively light gas whioh would become easily dispersed, cyanogen fluoride is not well suited as a war gas. Finally respirator oharooal now in use offers fairly adequate protec­ tion against this gas. -17­

B. ME.ASURNviENTS OF THE SERVICE TIME OF RESPIRATOR CHARcOAts FOR POISON GASES I. INTRODUCTION

This investigation was undertaken with the purpose of obtaining information on the effioienoy of absorption ot a number of potential war gases by aotivated respirator char­ coal. An attempt was made to approximate as nearly as possible aotual field conditions. Briefly, the method consisted in passing air ot oontrolled humidity and containing known conoentrations of poison gas through a charcoal bed at a known rate. The servioe time in this oonneotion is defined as the time in minutes re­ quired until the gas passes the charooal bed at sufficient concen tration to resp ond to a chemical test. Ordinary respirator charcoal now in cammon use, and whioh may be derived from cocoanut, beeChwood or some other source, is prepared in granular form and activated with dry steam. The aotivated prOduct oontains apprOXimately 16% moisture. In addition respirator charcoals now in use are generally impregnated with some metal. The moisture oontent of the aotive charcoal is an important faotor in the absorption behavior of the charooal. It is therefore neoessary to store the charcoal in moisture ­ proof containers. Furthermore, because the behavior of the charcoal depends on its moisture content, the relative -18­ humidity of the air becomes an important factor, since extreme hlli~idity conditions of the air may alter the mois­ ture content of the charcoal. In meaalring the service time of any particular charcoal sample it is therefore necessary to take into account the relative humidity of the air which passes through the charcoal. In addition to this there is the possible effect, which the moisture in the air may have on the poison gas itself.

The concentrat ion 0 f the gas to be taken into account is a factor which may be variable within wide limite. The concentration necessary to be effective in the field will depend on the toxicity of the gas, but in general this con­ centration is likely to fall within the limits of 1 in 10,000* to 1 in 200 in exceptional cases. From the point of view of protection against the gas, the upper limit of concentration is of more immediate concern. A concentration of 1 in 100 is considered very exceptional under field conditions, and although most of the tests will be carried out for a concentra­ tion of 1 in 200, a concentration of 1 in 100 was also tested.

II. APPARATUS The apparatus consisted essentially of an assembly by means of which an air stream could be humidified to a desired humidity, and mixed with sufficient gas to maintain

:1 All concentrations will be indicated as parts by volume TO " HYVAG CHAR'OAL CELL. f -­-­ --===::::;"\ -~ -r O i I H

Alit IN LIT (r-- -,1 r~=o=:. r;=== +-­

c A

FIG. 3 -19­

a oonstant and known oonoentration of the gas. By means of an automatio pumping arrangement, the gas-air stream oould be drawn through the oharooal oell intermittently in a manner whioh approximated the behavior of the human lung. The gas-air mixing apparatus is shown in Fig. 3. Air is drawn through the humidifiers at A, passes through the glass wool filter at B, and into the 50 litre mixing volume C. S is a motor-driven stirrer fitted with three flexible blades, and a meroury oup seal at G. The poison gas is introduced into the apparatus through a ground joint at F. H is a liquid air trap whioh proteots the oil pump.

Two storage volumes ar e also provided. The burette L (100 00. oapaoity) is oonneoted to a meroury reservoir by means of whioh the gas is fed into the air stream at K. Fig. 4 shows the oharooal oell and the pumping assembly. Immediately behind the cellis the test chamber, which is oonneoted to a by-pass by means of whioh the test ohamber could be conneoted into or out of the air stream as desired. The test paper is suspended in the test chamber. The pmnping uechanism is a modified form of auto­ matic Toepler pump (6). When the oil pump is started mercury is drawn up into the large bulb D, which causes the mercury to be drawn down the other arm C. This causes the thread of mercury between C and B to break, the remaining mercury in B is sucked up through the arm A into D, so that D is moment­ arily open to the atmosphere, But this causes the meroury in FIG. 4 -20­

C to rise agal n to its former level and meroury flows into B and up through tube A into D. The aotion then repeats itself, resulting in a periodio suotion in the arm E, whioh is oonneoted to two meroury reservoirs as shown in Fig. 4.

Suotion in the arm E will oau se the Ire roury torise in the first bottle and oreate a suotion in the seoond. When the pressure in E is again a tmospherio the :meroury returns to its former level. Henoe the mercury in the second bottle moves periodioally up and down, oausing an alternate suotion and expulsion of air, and approximates therefore the behavior of the human lung. Two Bunsen-type valves are attaohed as illustrated, and permit the air-gas mixture to be drawn through the oell and test ohamber via the first valve, and is then expelled through the seoond valve. The Bunsen valves were made from flexible rubber tubing, about 4 om. in diameter, suoh as is supplied for use with Gooch oruoibles. A length of about 7 om. was slipped over a pieoe of glass tubing, and the other end was flattened down and oemented with rubber oeJ:nent, leaving an opening of about 1 em. The glass tubing was then fitted into the neok of a 300 00. round bottom flask having an outlet tube as Shown, and oemented in position with de Khotinsky cement. On exhala­ tion the rubber tube of the first valve oollapses, and opens on inhalation. The seoond valve is reversed to that of the first and opens for exhalation and oloses for inhalation.

The rate of "breathing" oould be oontrolled wi thin oertain limits by raising or lowering the depth of the tube E -21­

in the first reservoir; lowering the tube into the bottle decreased the rate of breathing, and raising the tube in­ oreased it. In this way the volume of the "breath" or puff could be controlled. The actual rate of flow is further dependent on the number of puffs per minute. This is deter­ mined by the dimensions of the apparatus, that is, the volume of air in the bulb D and in the first reservoir of the "lung" and also by the rate of evaouation of the oil pump_ By partially shutting off the stopcook on arm D the number of puffs could be varied to a considerable degree. With the apparatu s used the number of puffs per minute oould be ad­ justed from 12 to 16, which is about the normal number in human breathing. The dimensions of the charcoal cell were chosen so that the volume of the charcoal bed was one-eighth that of a standard res9irator canister. It had an inside diameter of 3.5 am. A sintered glass disc was fused into the oell, which formed the bottom boundary of the charcoal bed, and a re~ovable sintered glass diso was placed on top of the bed. The cell had further three oorrugations in the wall above the lower diso, whioh made it similar in design to that of a re­ spirator oanister. When in use the oell was packed with charcoal to a height of 5.2 em. Since this volume of charcoal correspomed to one-eighth of the volume of the respirator canister, the overall rate of flow in the apparatus had to be adj usted to -22­ one-eighth of the normal human breathing rate. The latter, for a man sitting or lying quietly, is approximately 8 litres per minute (a man exercising breathes abou t 4 times as fast). Most of the experiments were carried out with a rate ot flow of one-litre per minute, although in many cases a flow rate of two litres per minute was also used, and represents a breathing rate of 16 liters per minute, which would correspond to a man walking or doing other mild exercise.

III. EXPERIMENTAL (a) General Prooedure: Preparatory to an experiment the rate of low of the apparatus was oalibrated by collecting the air from the outlet valve, and measuring the time required to displaoe 5 litres of water. The adjustment of the rate of flow had to be made by trial and error by moving the tube E (Fig.4) until the desired rate was obtained. Before an experiment the relative humidity of the air in the mixing volume had to be adjusted. The stirrer was started and air was drawn through the apparatus for a period of one and one half to two hours. The humidifi er A (fig. 3) conSisted of three Winchester bottles containing dilute sulfuric acid having a specific gravity of 1.26. The relative hmuidity of air above this solution is 66~ (7). The specific gravity of the acid solution was frequently checked with a hydrometer, and adjusted when neoessary. -23­

The cell was charged by adding the charcoal in four portions and tapping the cell after each addition, the tapping being both vertical and on the side of the cell by means of a piece of wood. These precautions were necess­ ary to obtain reproducible packings. The cell was packed to a height of 5.2 cm., measured after the removable s:i nter ed disc was pressed on the top of the charcoal bed. The cover of the cell was then placed in position, and the oell was attached to the apparatus. The pOison gas was introduoed into the apparatus through the ground joint F (Fig.3) and condensed in the bulb E, where it was fractionated. The first and last fractions were discarded, and the middle fraction was condensed in the bulb D. The stopcock at 0 was then closed. The burette L was filled by warming the bulb D. Sufficient gas was added to the minng volume at the beginning of the experiment to obtain the de­ sired conoentration. With the oell in place, the pumping system was started and the time reoorded. SuffiCient gas was then fed from the burette into the air stream at one minl~lte intervals to keep the concentration of gas in the mix­ ing volume constant; the amount of gas necessary could be calculated from the rate of flow of the air stream. The test chamber was connected into the air stream at fre~ent intervals, and the time was noted when a definite color change was observed on the test paper. This was recorded as the

servi ce time. -24­

When the apparatus was in operation a series ot runs could be made, but if a change of concentration or humidity was desired, or before beginning a series of runs the follovTing day, air had to be blown through the apparatus to sweep out the pOison gas until a negative test was shown by the test paper. (b) Charcoal Samples Used: In all of this work the charcoal samples used were chiefly of two kinds: (1) Wbetlerite Charcoal- A respirator charcoal, activated by steam and impregnated with copper. Its moisture content was about 16% by weight. (2) English Charcoal - This product was derived from activated cocoanut charcoal and was impregnated with silver. The mOisture content was of the order of 15%. An unimpregnated sample of this charcoal (desi gnated as A-8?) was also used in some experiments. It should be mentioned in this connection that the portions of charcoal used in the following experiments did not all belong to the same lot. Charcoal samples were reoeived in bulk in the laboratory from time to time, and the different lots varied somewhat both with respect to their servioe times and their moisture conten't. Whether or not there is a direct relationship between these two factors was not investigated here. In most oases however, the date the oharcoal samples were received will be indic ated to aid in differentiating them. -25­

(0) Experiments with Arsine (1) Preparation of Arsine Arsine was prepared by the action of water on calCium arsenide, according to the equation:

OaaAs2 + 6 H20 --. 2 AsH3 + 3 Oa(OH)2 The calcium arsenide was prepared by fusing powdered metallic arsenic with oalcium metal in a 6-inch crucible. The apparatus for the preparation of arsine is illustrated in Fig.5. The tube A containing the powdered arsenide, fits into a ground joint at B. The one-litre flask 0 was half filled with water, and was surrounded by an ice bath D. Arsine is readily de­ composed by heat. By adding the calcium arsenide gradually to a relatively large amount of water, which in turn is kept at a low temperature, the heat ot reaction is largely dissi­ pated. The arsenide was added gradually by turning the arm A through an angle slightly greater than 90°. E and F are two traps surrounded by an acetone-ba th at -25°0. by means ot which the product was freed of water vapor. The arsine was condensed in G with liquid air. The first and last fract ions were discarded, and the middle fraction was used in the servioe time experiments. Arsine has a boiling point of -55°0. On storing at room temperature the gas gradually decomposed, forming a black mirror-like deposit on the walls of the apparatus. It was therefore necessary to store the gas at liquid air tempera­ tures. TO VACllUM

E G

o - - - -

FIG. 5 -26'"

The test used to detect the gas in the service time experiments was the well knovm Gutzeit test. Filter paper was impregnated with a concentrated solution of merwnc

chloride, drie'd and out in small strips t whioh could be plaoed in the test chamber of the apparatus. The limit of sensitivity of this test is about 1 in 200,000. The service time was recorded as the time when a distinot yellow oolora­ tion of the test paper was visible. The toxioity of arsine has been studied by the United States Department of Sci entifio and Industrial Re­ search (a). Aooording to these results a concentratia1 of 1:20,000 produoed dangerous results in one hour, while a 12 hour exposure with a concentration of 1:200,000 was reported as fatal. (2) Results of SerVice Time Measurements with Arane After a few preliminary runs had been carried out to oalibrate the apparatus, the first experiments on service time measurements were made with arsine. These were oarried out with seme oharooal sarllples, Whetlerite, English Charooal and English A-a?, reoeived March 5, 1940. The relative humi­ dity of the air was controlled at 66%, and arsine conoent ra­ tions of 1:200 and 1:400 were used. The Whetlerite s8IIJ?le as reoeived contained 18.a% moisture. A portion of this was dried over phosphorus pentoxide in vaouo, whioh reduced the moisture content to 3.a%. Enough of this partially dried material was mixed with a portion of the original sample to bring the total mOisture content to 16%. The results of these experiments are summarized in Table III. -27­

TABLE III Servioe Times for Arsine

Rate of Cone "Arsine Charcoal .. Air Servioe Time flow (Min. ) English 2 Litres/min. 1:200 50 53 Mean 57 tt tt _ -"­ U _ _ _ _ _ 1:400 116

English A-87 1:200 3.5 3.5 Mean 3.5 ------Whetlerite (18.8% moisture) " 1:200 41 34 Mean 38 ------Wbetlerite (16.0% mOistura) " 1:200 25 35 32 Mean 31 1:400 75 73 Mean 74

According to these results the English silver- impregnated charcoal is nearly twiee as efficient as the Whetlerite, copper impregnat ed charcoal contai ning 16.0% moisture. However Whetlerite samples received later were much more effieient. Here as in some later experiments, doubling the conoentration of gas gi ves approximately half the service time, but the relationship is by no means exact, and is probably dependen t on the mechanism of the absorption process, which for any particular gas may be a simple adsorption, -28­

or a hydrolysis, oxidation or some other catalytic reacticn, or a combination of these. The effect of impregnation of the active charcoal with either silver or copper is very apparent when the service times of the English and Whetlerite charcoals are compared

, with that of the English A-8? charcoal; the latter is un1m­

pregnated ~~d has a service time of but 3.5 minutes. The flow rate of 2 litres per minute used in the above experiments is twice the normal breathing rate, and corresponds to the breathing rate of a man exercising mildly.

Furthermore a concentration of 1 in 200 is high under field

conditions. A service time of half an hour is generally con~ sidered adequate protection under the above conditions. According to the above experiments both the tinpregnated English charcoal and the Whetlerite charcoal provide adequate protection against arsine. Two new samples of Whetlerite and English Unpreg­ nsted charcoal were received March 20, 1940. These were tested as before, and the results are tabulated in Table IV. TABLE IV Service Times for Arsine (Relative Humidity of the Air = 66%) Cone: Arsine Service Time Charcoal Rate of flow air (Min ) Whetlerite 2 1itres/min 1:200 1U3 123 122 Mean 121 ------English 50 " " 50 52 Mean 51 -29­

On oomparing Table III and Table IV the variation of' the servioe times for different lots of charcoal is very apparent, the new sample of Whetlerite being almost four times as efficient as the first sample. The history of the different charcoal samples submitted from time to time was not disolosed, and is inconse­ quential as far as the purpose of' the present work is ooncerned. In the course of the above experiments it was observed that a very considerable amount of heat developed when the arsi ne was taken up by the charcoal. The charcoal oel1 beoame quite warm, expelling large amounts of' moisture which condensed on the walls of the apparatus below the charcoal bed. Since it was at first oonsidered probable that the absorption mechanism involved a hydrolysis, and sinoe the expulsion of the moisture f'rom the charcoal may affect the service time, a study of the effect of varying the relative humidity of the ingoing air was considered worthwhile. The results of this investigation are summarized

in Table V. TABLE V Effect of Variation of the Relative Humidity Rate of flow - 2 litres/min. Concentration: arsine/air = 1/200 Charcoal samples sane as in Table IV Service Time (Min.) Relative Humidity English Charcoal Whetlerite 43 70 37 90 Mean 40 80 - ~ ------­ 50 119 50 122 52 123 51 121 - ~ - - ~ - - -- ~ ------­ - .. -­ 0-10% . 120 122 129 124 -30­

A relative humidity of 90-100% was obtained by bubbling the lngoing air through water, while a relative humidity of 0-10% was obtained by bubbling the air through concentrated sulfuric acid. Since these values of the re­ lative humidity were not determined exactly, a variation ot 10% is allowed.

The results indicate quite definitely that the service time is less for very moist air, and very consider­ ably greater with dry air. The results moreover do not point to a hydrolysis meohanism for the absorption process. It is conceivable however, that dry air passing through the cell might remove moisture condensed on the active centers of the charcoal, and hence allow the arsine to reach these centers more readily. With a moist air stream, the mOisture already present on the charcoal would not be desorbed as readily, and thus less surface would be available to th~ arsine, resulting in a shorter service t iDle. Valuable informat ion coul d be obtained on this question by varying the moisture content ot the oharooal itself, but due to more urgent prOblems, the matter was investigated no further. Another factor whioh may heve same bearing on the variation of the service times with relative humidity is the sensitivity of the test for arsine. If the test becomes less sensitive for dry air, the variation in service times might be explained, but it is unlikely that this source would lead to as great a variation in the service times with the relative humidity as is Observed. -31­

Some additional experiments were performed with arsine for a rate of flow of 1 litre per minute, and also for a concentration of 1:100. These results are shown in

Table VI. The experiments were carried out with English Charc 001 only. TABLE VI Effeot of Variation of Flow Rate and Concentration Relative humidity = 90-l00~ .Arsine Serv Co n.C Air low: 1 litre

1:200 81 43 88 37 Mean 85 40

1:100 39

As might be expected, since the same total amount ot gas passes through the charcoal bed, a concentration of 1:200 at 2 litres/min. gives the same service time as a concentration of 1:100 at 1 litre/min. In as much as the above experiments represent severe field oonditions, the oharcoal samples tested are considered to offer fairly adequate proteotion against arsine. (d) Exoeriments with Phosphorus Trifluoride: (1) Preparation of Phosphorus Trifluoride: Phosphorus trifluoride was prepared by means of the reaction between antimony trifluoride and phosphorus trichloride with antimony pentachloride as a catalyst (9,10): PCla + SbFa --+ PFa + SbCla -32­

This type of reaction has been recently studied by Booth ana co-workers (11), and it is from their results that this prooedure was adopted. The apparatus consisted of a three litre, three-neoked reaction flask fitted with a worm teed, a dry ice-acetone oon denser , a stirrer and a dropping funnel. The outlet of the condenser was joined to a condensing bulb and storage volumes. About 85 grams of phosphorus trichloride were placed in the reaction flask, and warmed up to 40°0. by means of a water bath. One cubic oent~eter of antimony pentachloride was then added, and powdered freshly sublimed antimony tri­ flu oride was gradually added. The dry ice-acetone condenser prevented the by-produots PF01 2 and PF20l, whi ch have an appreciable vapor pressure at 40°0., from contaminating the product. The product was condensed and purified by fractional dist illation. The test used for detecting phosphorus trifluoride in the service time measurements was as follows: A saturated solution of silVer nitrate was prepared, and concentrated ammonia added until the precipitate, which first formed, dissolved. A strip of filter paper muistened with this solu­ tion gave a dark brown to black coloration in the presence of phosphorus trifluoride. Brown coloration of the test paper can be obtained with phosphorus trifluoride-air mixtures of the order of 1:7000, while blaokening occurs at a concentrati01 of abou t 1:3000. In the servi ce time meafU rements, the brown coloration of the test paper was taken as the end point. The toxicity of phosphorus trifluoride has been tested at the University of Toronto: With a gas conoentration of 1:4000, one of 25 rats died after a 23 minute exposure, while for a concentration of 1:1000 an d a 6 minute expo Sl re only 4 rats died. For a man it is unlikely that these con­ centrations are as toxic, especially for short exposures. However, more thorough studies of the toxicity of phosphorus trifluoride will no doubt be made. (2) Results of Servioe Time Measurements with Phosphorus Trifluoride: Preliminary experiments showed that with phosphorus trifluoride a relatively short servioe time of the order of 5 minutes was obtained. The rate of flow was 2 litres per minute. To substantiate this a large number of runs were oarried out. The results are tabulated in Table VII. Two end pOints for the servioe time are reported, the first re­ presents the pOint where the first distinct brown ooloration of the test paper was noted, and the second when the test paper turned dark brown to blaok. The first end point therefore corresponds to a concentration of gas leaking through the charooal of about 1 in 7000, and the seoond end paint 1 in 6000 to about 1 in 4000. This gives a rough indication of the conoentration of poison gas passing the charooal at the point of break-down. -34­

TABLE VII Service Times for Phosphorus Trifluoride Rate of flow = 2 litres per minute Conoentration PF3/air = 1/200 Relative humidity = 66%

Charooal Service Time (Min.) ______F_i_r_s_t__e_n_d~-point Seoond end-point

English 4 10 :3 10 3-1/2 10 4-1/2 8 4 8 5 10 4 9 5 Mean 4-1/2 -9

'i1hetlerite 5 12 7 13 12*1/2 lr* 18. 11-1/2* 16.... 9 13 8 12 9 12 9 12-1/2

.. In these two experiments the purity of the gas used was doubtful. From these experiments it is apparent that for a rate of flow of 2 litres per minute, which corresponds to a fairly active breathing rate, the English charcoal and the Whetlerite do not provide adequate protection against phos­ phorus trifluoride; the Whetlerite sample is slightly more effeotive than the English Charcoal. It will be shown later, however, that there is a considerable safety margin when the rate of flow corresponds to the normal breathing rate. -35­

Some further experiments were carried out in whioh the relative humidity of the air was varied. These results are recorded in Table VIII. TABLE VIII Effect of Variation of the Relative Humidity Rate of flow = 2 litres/min. Conc. PF3/air = 1/200

Servi ce Time (Min.)* Relative humidity English Charcoal Whetlerite CW3**

0-10s' 9 14 66% 4-1/2 9 90-100% 4-1/2 7-1/2 5-1/2

* The service times recorded here and in the tables following represent the average of two or more exp eriments, and are the first end-points only.

** CW3 was a new s~~ple of Whetlerite received April 21, 1940. The results of Table VIII follow the same general variation of service times with humidity as was noted with arsine, the service time for very moist air is about half that for dry air. The humidity of the air is therefore an important factor to be considered in the field. Here as with arsine it is difficult to explain the effect of the humidity without a knowledge of the role which the moisture on the oharcoal as well as that of the air plays in the absorption prooess. Further experiments were oonduoted to examine the servioe time for a rate of flow of one litre per minute. These results are oompared in Table IX with the servioe times for a flow rate of 2 litres per minute, and for three different values of the relative humidity. -36­

TABLE IX Effect of Variation of the Flow Rate Conc : !i: = 260

Charcoal Relative Humidity low: 2 English Charcoal 0-10% 9 80 66% 4-1/2 35 90-100% 4-1/2 43 -- - ... ------.. Whetlerite 0-10% 14 114 66% 9 39-1/2 90-100% 7-1/2 III

There is a large difference in the service time for a flow rate of 2 litres per minute, and for a flow of 1 litre per minute. Moreover for a rate of flow of 1 litre per minute there is not the same regular gradation of servi ce times with the relative humidity, but rather the service time is shorter for the intermediate humidity of 66%. It should be pOinted out here that while the absorption process was highly exo­ thermic for arsine, only a very slight amount of heat is de­ veloped when phosphorous trifluoride is taken up by the ohar­ coal. With the rate of flow kept constant at one litre per minute J some measurements were al so made for a ooncentra.­ tion of phosphorus trifluoride:air of 1:100. These results are shown in Table X. TABLE X Effeot of Variation of the Concentration of Phosphorus Trifluoride

English 0-100% 80 42 Charcoal 90-100% 43 28 -- -- ­ - ~ ~ - - - -- ­ - - - - Whetlerite ·0-10% 114 63 90-100% 111 42

The rasults of Table :IX: and Table X show that for a flow rate of one litre per minute, which corresponds to the normal breathing rate, both charcoals provide fairly adequate protection even for concentrations as high as 1 in 100, while for a more active breathing rate, corresponding to a flow rate of 2 litres per minute in these experiments, the protec­ tion by both charcoals against phosphorus trifluoride is not quite adequate. The rate of flow is apparently a oritioal factor in this case. It must be borne in mind that when the flow rate is 2 litres per minute, the gas-air mixture actually passes the charcoal at a rate of approxnnately 4 litres per minute, since the flow consis ts of a series of puffs. If there are, for example, 12 puffs per minute, then eaoh puff moves a volume of gas-air of 167 cubic oentimeters, while between puffs there is no flow through the charcoal bed. Therefore, for an overall rate of flow of 2 litres per minute, the velooity of the air stream during the ffinhalation" period may be so rapid that all -38­

of the gas molecules are not able to come in contact with the surface of the charcoal particles. It is possible there­ fore that a "channeling" ooourred for a flow rate of 2 1itres per minute, and the gas was thus able to leak through. This would explain the short service times for a flow rate of 2 litres per minute, and also, if a stoichiometrical reaotion is involved, why the service time is not the same for a oon­ oentration of 1:200 and a flow rate of 2 1itres per minute, as for a concentration of 1:100 and a flow rate of one litre per minute; in both cases the same total amount of gas passes through the charcoal cell. However, on the supposition of a

"channeling" occuring for a flow rate of 2 litres per minute it is difficult to explain why this effect was not observed for arsine and phosgene, In this connection several experiments were oarried out using a continuous flow of the air-gas stream rather than an intermittent flow. The continuous flow was obtained by using the same pumping arrangement as before and placing in series with the air stream a 50 litre "surge" volume between the charcoal cell and the inlet valve (Fig.4). The results of these experiments for a flow rate of 2 1itres per minute are recorded in Table XI, and are oompared with those for an intermittent flow of 2 litres per minute under the same conditions of oonoentration and hlli~idity. -39­

TABLE XI Comparison of Continuous and Intermittent Flow Conoentration: PFs/air - 1/200 Relative humidity = 56% Overall flow rate • 2 litres per minute

Charooal Servi ce Time (Min.) Intermittent Flow Continuous Hlow

English oharcoal 4-1/2 19 English A-8? 5 19 Whetlerite 9 :1.2-1/2

In acoordanoe with the above disoussion the servioe time should be longer for a continuous flow than for an inter­ mittent one. But the differenoe observed is not as great as might be expeoted; if the flow rate is the determining faotor, then the service time for a oontinuous flow at a rate of 2 Iitres per minute should be of the same order as for an intermittent flow of one liter per minute, for the same oonoentration of gas (See Table IX). As a final phase of the work on phosphorus tri­ fluoride, several attempts were made to find some absorbing substanoe whioh could be used in oonjunction with oharooa1, and wh i ch would absorb phosphorus trif1uori de more eff:ioient1y.

These substanoes included si1ioa gel t potassium hydroxide, soda lime, alumina, cuprene and hopoa1ite. These were found unsatisfaotory as absorbents, exoept hopoalite whioh gave a service time of about 35 minutes for a flow rate of 2 1itres perminute and a conoentration of 1 in 200. -40­

(e) Experiments with Phosgene The above experiments on the measurement of service times of respirator charcoal were oarried out in conjunotion with similar measurements by the National Research Council in Ottawa. The a.pparatus used in the two labcratories differed in several respects; in the Ottawa laboratory the service time was measured directly with a respirator oanister, in place of the oharooal oell. This involved a rate offiow of the gas-air mixture eight times that used in this laboratory. Sinoe the service time measurements involve a number of variable faotors (e.g. hwuidity, temperature, conoentration and manner of flow) and if the results are to be comparable, it was necessary to compare the apparatus in the two laboratories. To do this certain conditions were arbitrarily chosen as standard, and phosgene was chosen as a reference gas. In this way it was hODed to determine the "apparatus constanttt of the apparatus used in this laboratory and thus faoilitate the comparison of the service time measurements. (1) Construotion of a Small Service Time Apparatus. In this conneotion it was also considered advantage­ ous to construct another service time apparatus, but on a still smaller soale• With this a pp~}ratus very much smaller amounts of gas would be neoessary, which is a decided advantage for experimental purposes, when the gas to be studied is difficult to prepare by a laboratory ::uethod. -40"-'

Moreover, if absorbents other than charcoal are to be studied, only small amounts of these would be required. The .ileW assembly was built along the same general plan as that already described. A flow meter was attached to the air inlet (Fig.5) so that the flow rate could be followed during the course of en experiment, and could be adjusted by means of a mercury reservoir attached to the "lung", part of the apparatus. A 5 litre mixing volume was used and the gas­ air inlet tube was sealed on the bottom. The charcoal cell had an inside diameter of 1.2 em. (The height of the charcoal bed was again 5.2 em.) In order to heve the results of the two assemblies directly comparable, the rate of flow of the snal1er apparatus was adjusted so as to give the same "space velocityff through the charcoal bed as in the rger apparatus. This was cal­ culated from the ratios of thA square of the diameters of the lArge and small cell; corresponding to 2 Ii tres per minute, a flow of 235 cubic oentimeters per minute was used tor the small assembly. (2) Results of Comparison Measurements Vii th Phosgene: For the detection of phosgene, the dimethylamino­ benzaldehyde-diphenylamine test paper (4) was used. The limit of sensitivity of this t est is 1 :800,000. {The lethal con­ centratiol1 of phosgene for 2 30 minute exposure is about

1: 50,000 (12)). -41­

The conditions chosen for the comparison experi­ ments were: (1) Relative humidity = 66% (2) Concentration: 12hossene 1 air :: 100 (3) Rates of' flow: Ottawa apparatus 16 11tres/minute McGill Large tf - 2 " tt McGill Small " 0.235 tt For these experiments five samples of \Vhetlerite supplied by the National Research Council (May 22, 1940) were used. The results are tabulated in Table XII. TABLE nI Comparison of Service Times for Phosgene

Charcoal Service Time fMinl. Small Apparatus Large Apparatus Ottawa Ipparatus

CWl 82 90 35 CW2 68 72 39 CW3 68 80 33 CW4 73 73 36 CW5 86 93 31

The agreement is no t good. Comparing the first two columns, the small apparatus gave slightly shorter service times. Moreover it was found that with the small ap?aratus more reproducible and consistent results were obtained than with the large assembly; the figures in Table XII represent the average of two or more measurements on each charcoal sample. A. much greater discrepancy is apparent when the first two -42­

columns are compared with the results ot the Ottawa apparatus; the latter resul ts are only about half the value of the tormer, and the variation in service time from one charcoal sample to the next is not in the same order. Four additional Whetlerite charcoal samples were supplied (Received July 20, 1940) and were tested as before. The results are recorded in Table XIII. TABLE XIII Comparison of Service Times for Phosgene

Servi ce Time (Min.) Charcoal Small apparatus Large apparatus

eW5 88 55 CW7 85 83 ewe 88 81 CW9 92 70

The results at the Ottawa apparatus for these samples were not available. The agreement between the re­ sults of the large and small apparatus is not consistent; contrary to the results of Table XII, the service times of the large apparatus are generally somewhat shorter than those of the small apparatus. There are several factors which may have a bearing on these inconsistencies: (1) The temperature of the absorption cell may account for a part of the discrepancy. The larger the char­ coal cell, the higher the temperature which is attained as a result of the absorption process. This can be explained by -43­ the small heat conductivity of charcoal; for a large char­ coal bed, less h~at is disSipated from the interior.

(2) The relative humidity of the air was not measured after it had passed the humidifiers, nor was any attempt made to correct the relative hum.idity of the air stream for changes in the temperature of the room. Changes in the absolute humidity of the air may be a serious factor in the case of phosgene where a certain amount of vapor phase hydrolysis probably occurs in the mixing volume of the apparatus. (3) A sintered glass disc was fused into the ab­ sorption cells as a support for the charcoal bed. Partial fusion of the disc itself, which took place in this opera­ tion, especially in the small cell, offered considerable resistance to the air stream. This would tend to smooth out the breathing pulsations of the flow, which would result in a longer service time. In the Ottaw2 assembly no sintered glass discs were used. If this factor were appreciable how­ ever, there should be a greater difference between the service times of the large and small apparatus in this laboratory, since the small cell had a much greater resistance to an air stream.. The above experliuents on the comparison of service times of the different assemblies led to the design of a new apparatus, which is now being used in this laboratory by other -44­ investigators. The mixing volume was dispensed with, and the gas is being added continuously into the air stream from a burette into which mercury flows from a reservoir at a pre­ determined rate. The relative humidity of the air is measured by a wet and dry bulb ther~ometer in series with the air stream, and can be adjusted when necessary. Finally, a new charcoal cell is being used in which the charcoal bed is supported by a brass screen, rather than a sintered glass disc. (f) Exoeriments with Cyanogen Fluoride (1) Preparation of Cyanogen Fluoride (See Part A) (2) Test for the Detection of Cyanogen Fllloride The test used was briefly as follows: Cyanogen fluoride, or air containing it, was passed through a red hot (600-700°C.) silica tube, packed with copper oxide. The gases after passing through the furnace were tested with dtmethyl­ amino-benzaldehyde-diphenylamine paper (4). In the presence of cyanogen fluoride the paper was colored yellow-orange. The sensitivity of thi s test was investigated. Cyanogen fluoride-air mixtures of known ooncentrations were drawn through the furnace at the same rate used in the service time measurements with the small apparatus (0.235 litres/min.). The results are indicated in Table XIV. TABLE XIV Sensitivity of Cyanogen Fluoride Test Concen tration Time for a positive cyanogen fluoride:air paper test 1:1000 3-5 minutes 1:400 40-50 seconds 1:100 instantaneOl S -45­

For concentrations less than 1:1000 the test is less satisfactory, as a relatively longer time is necessary. A blank test with air alone gave b'Jt a faint yellow coloration after 25 minutes, which did not increase in intensity after two hours. With some experience allowance oan easily be made for this, and it is possible to detect concentrations less than 1:1000, but caution must be exercised. As mentioned in Section A, cyanogen fluoride is toxic at a concentration of 1:1000, but only under conditions of relatively long exposure.

(3) Results of Service Time Measurements with cyanogen fluoride. As cyanogen fluoride was difficult to prepare the small testing assembly was used, and the testing apparatus des­ cribed above was connected into the air stream ~ediately after the absorption cell. The results are tabulated in

Table XV. TABLE XV

Results of Service Tll~e Measurements with Cyanogen Fluoride. Concentration: Cyanogen Fluoride/air = 1/100 Relative Humidity - 66% Rate of flow = 0.235 litres per minute Servi ce Time (Min .1 Whetlerite CW2 English Charcoal Series I 19­ 9 ff II 21 10 ff III 19 IV 17 "tf V 17 S " VI 17 a The figures in Table XV represent the average of two or more experiments. Each series was carried out with a sample of gas from a separate preparltion. It was observed during the course of these experiments that the cyanogen fluoride had to be carefully purified. In the later series only the first fraction of a sample of the pure gas was ~ployed and this gave more consistent and reproducible results. The last fraction of gas in any sample was considerably less volatile than the first fraction, and as mentioned in Part A, may be attributed to polymerization whioh is oommon to the oyanogen halides. The servioe times tabulated in Table XV represent the time for a definite coloration of the test paper to develop.

In order to obtain some idea of the ooncentration of gas pass M ing the charooal at this stage, a new test paper was inserted in the test ohamber and the experiment oontinued. It was found that 8-7 minutes were required for the new paper to develop a positive coloration. From this it may be estimated, consider~ iog the sensitivity or the test used (Table XIV) that the con­ centration of gas passing the charcoal at this stage is con­ siderably less than 1:1000 and may be of the order of 1:2000. Some experiments were also carried out using a gas­ air ooncentration at 1:200, the relative humidity and flow rate remaining constant. For Whetlerite (CW2) a servioe time of 38 minutes was obtained. This is about twice the service time for a ooncentration of 1:100. -47­

The rate of flow used here corresponds to a rather active breathing rate. Since cyanogen fluoride is not appre­ Ciably toxio at concentrations less than 1:1000, and since

after 38 minutes conoentration of the gas passing the charooal is still less than 1:1000, the protection provided by the Whetlerite charcoal is considered fairly adequate. Hopoalite was also tried as an absorbent for cyano­ gen fluoride. It was found however, that with an equal volume of hopcalite and a concentration of 1:100, a service time of only 5 minutes was obtained.

IV. GENERAL CONCLUSIONS In the course of the preceding pages the experimental results of the service time measurements have been co~nented upon. These results may be very briefly summarized as follows: From the sensitivity of the test used in detecting the pOison gas, an estimate of the concentration of the gas passing the charcoal at the break-down point oan be made. If the point of break-down of the charcoal (that is, the service time) for a nor.mal breathing rate is of the order of half an hour, and if the concentration of the gas leaking through at this pOint is not toxic, the charcoal is considered to provide adequate protection against the gas. Although this was found to be the case for arsine, phosgene, phosphorus trifluoride and cyanogen fluoride, for a more active breathing rate, the proteo­ tion by the oharcoals studied against the last two 8ases is not Quite sufficient, and a greater tfsafety margin" would be -48­

BIBLIOGRAPHY

(1) Coss1ett, V.E. Zeit. Anorg. Chem. 201, 75 (1931). (2) White and Goodeve. Trans. Far. Soc. 30, 1049 (1934). (3) Hildebrand, J. "Solubility", 1935, p.31. (4) Sartori. "The War Gases", 1938, p. 81. ( 5) Lunge and Ambler. Technical Gas Analysis, p. 297.

(6) Maass, O. Journ. ~ner. Chem. Soc. 41, 53 (1919). (7) Wilson, R.E. Ind. & Eng. Chem. 13, 328 (1921). (8) Leaflet No.9. U.S. Dept. of Soient. & Ind. Research. (9) Moissan, H. Ann. Chim. Phys. 6, 433 (1885). C.R. Acad. Soi. Paris 100, 272 (1885). ( 10 ) Ruff, O. Die Che::nie des F1uors. p. 27, 1920. (11) Booth, Hard Bogarth, H. Journ. Amer. Chem. Soc. 61,2927(1939). (12) Vedder, E.B. "Medical Aspects of Chemioal Warfare", p .83, 1925. PART II.

AN INVllBTIGA.TION OF THE PHYSICAL PROPERTIES OF A 'lW0­

COMPONmT SYSTPl4 IN THE CRITICAL ~ERA.TUU. CRITICAL

PRESSURE REGION. I. mSTORICAL IN'lRODUCTIO!j:

the phenomena occuring at tho critical tomperaturo ot a

8ubs~ce have been the subject ot a ser1es of researches in this laboratory, and the present investigation 1s a further continuation in this field. In order to appreciate tully the purpose and method ot this investigation, as well as the issues it involves, a brief survey ot the numerous works which have been published on crttical temperature phenomena is necessary and will conveniently serve to introduce the subJ'ct matter ot thie thesis.

~e detin!tion ot the cntical temperature as such is generally credited to Cagnaird de la Tour (1) who in )1822 Observed that when a liquid is heated in a sealed tube. the meniscus dis­ appears at a detinite temperature, the critical temperature. At this temperature, the visible line of' deme.iI'cation of' liquid and gas having disappeared, the system was believed to consist of' a highly compressed homogeneous gas. Later .Andrews (2) made a quantitative study of' this phenomena, and obtained the parabolio ourve representing the coexist­ ence boundaries for liquid and vapor up to the critical temperature region. 1he work ot Andrews togethea:- with that ot van der Waals (3) tormed the basis ot the classical theory ot the continuity ot state.

Andrews in studying the pressure - ~lume relations ot carbon di­ oxide tor various temperature", showed that the isothermal just below the critical temperature was contiguous to that just above the crit1cal temperature. This was interpretated as indicating a continuity of' state, -the gaseous and liquid states being only -2­

distant stages of the same condition of matter and are capable of passing into one another by a process of ~ continuous change". This

theory gained further acceptance trom the van der Waals equation of

state which was tound to give tair quantitative agreement for liquids

as well as gases. Ibreover, by a judiciOUSly chosen sequence of

temperature and pressure changes, the change of state trom liquid to

gas can be brought about in such a way that all physical properties

vary continuously.

As early as 1880 experimental evidence was accumulated

which pointed to the possibility of more complex changes taking

~lace at the critical temperature. According to the theory of con­

tinuity of state, the critical phenomena should occur only at one

specific density, the cr!tical density. De la Tour had already

observed that the meniscus was seen to disappear over a range of

densities, and Hein (4) fount the crttical phenomena tor carbon di­

oxide to occur when the mean density varies from 0.241 ~./ c.c.to

0.589 (!J.I1./c.c. To explain this density range, Ramsay (5) and ~am1n (6)

postulated that the liquid state exists above the critical temper­

ature,and although the density of the liquid and vapor become equal

at the critical temperature, there is a fundamental difference

between liquid and gas molecules. This difference was believed to

be due to the liquid molecules dittering in the number of atomic

constituents and hence at the critical temperature the system was

considered to be chemically heterogeneous, but homogeneous physically since the phases were considered to be mutually miscible in all proportions. Call1etet and Colardeau (7,8) aeemed to believe that the liquid and gaseous states persisted separately atter the critical temperature had been exceeded. To sUbstantiate this theorJ'. Cailletat and Hautteuille (9) experimented with iodine and carbon dionde in a tube. Abo...e the critical temperature. the lower portion ot the tube prev1ousl1 occupied by the liquid retained 1ts violet color. while the upper part ot the tube remained colorless• • 'l'.b.e denaity deter.m1nat1ona made by Odlletet. and later

Young (10) are subject to criticism. Meaa.....t. an made 1a such a way which required obunaUou upon 'ib.e poa111oA ot the meniscus. Of necessity readings had to be discontinued shortl1 below the oritioal temperature. Nevertheless the density temperature curves obtained were extrapolated in the torm. ot the classical parabola.

Ge.ll.tzine (ll) working with ethyl ether. made aCCJll'ate dena1ty measurements in the critical temperature region, and reported atditterence in denaity in the upper and lower part ot the tube ot the order ot 20 ~. which maintained itselt indetinitely. EVidence ot a heterogeneous 8ystem was obtained atter 4) or 7°0 above the crit1cal temperature. Small traces of impurities, notably air. were thought to be responsible, but experimental tubes with detinitely­ greater quantitiea ot air inoluded showed no ditterenee trom the results obtained in the tubes caretully tille4 to exclude air.

Young (12) repeated the experiments ot Galitzine using very care­ tully puritied material, and tailed to observe any heterogeneity in elens1ty. He therefore agreed with Galitzine that the denaity perais­ tence could be attributed to impurities. -4­

Gouy (13) attempted to explain the phenomena ot density persistence at the crittcal temperature simply by the effect ot the gravitational tield on the weight of the madium itselt. Because ot the high compressibility ot the system at the critical temperature this idea seemed plausible, and reoeived turther support froa Ruedy (14).

It was however demonstrated later that the density 4iscontinutty at the critical temperature was most pronounced at the point where the menisous was last aeen, whereas according to gnvitational theory there should be a gradual denaity gradient trom. the top to the bottom ot the tube. M:>reoTer the dena!ty ditterences calculated by taking account of the gravitational tield were insufficient to account tor the observed density differences.

In the next fifteen years. 1900 to 1915, tour investigators earned out experiments in which the density of the material in sealed tubes was measured by enolosing a series of marked glass tloats at Various known densities. These were Hein (15), de Been (16)

Kamerl1ngh ODnea and Fabius (17) and Teiehner and Traube (18), (19).

Their results were concordant in most respects. In particular it was found that a density difference did exist above the critical temperature, but the first three found that with time this density

'1tference disappeared. From. these researches, Teichner and 'lraube, de Heen and Rein opposed the classical theory of cont1nuity at state ot Andrews and van der Waals. annes and Fabius took the opposite view attributing the whole phenomenon at persistence to impurities and poor experimental methods.

As a result of these experiments Traube became the chiet proponent at the discont1nuity theory and postulated that there is 8ll ••s8Jltial 41fferenoe in oharao\er between liquId and gas. True liquid molecules were ter...Jl8d "llquidons I'f and true gaa molecules

"peons". The two speoles were consldered to exist in equilibrium.

As the temperature 1s raieed he considered the :aonoentration of

"llquldons" decreased while that ot the "gasons" increased•.At the oritioal t~perature some "l1quldone~ persIsted. De liGen extended

the hypotheais ot Traube by requIring that the ooncentration ot

"liquldone" 1s a funotion ot the W8as--volume ratio or the system u well as tha temperature.

Callandar (20) usina carefully purified \tater in a o sealed quartz tube obttlined a a&rullt1 d1rterenoe as high. 86 0 0 above the oritioal tamperature.

Solubility measurements carried out in the critical

MI3p8rature region in ;JeDeral pointed to a persistenoe ot liquid propertle. abOve the cr1tical temperature. Besides the work of

Call1etet and Hautetoul1le (9) already ment1oned, the experil:18D.ts ot Ha.nzu:a1 and Hogarth (21) with potassil..ll1 10<'11de -alcohol guYS s1n1lar results f 'lbe solute ws found to preclpit8t8 when the liquid just bolow the oritical tem<}orature W&6 heated, but 1t re~ned in solution at a temperature a11ghtly above the or1tical temperature. Because Q certain solvent powor ot the medium exlsteoaboTe the eritloal teapernturo, the results ware QOnsId~red to indicate the presence of liquid. 31nilar results were obtained by ilictet (22) who studIed borncal- and al1zar1n--aloohol solutlou. llowever the expen.:nenta or Ber'rand and Leoa.rme (23) are oOlltra41otor'1 and gave Videnoe of aqual ...... *1.. seluh11it~ in bo th phases at

the cr1tical temperaiu£e for salts in water and alizarln--Bloohol solutions. -6­

In addition to density and solubility. a tew researches

were carried out at about this time which ind1cated that O'iher properties also varied discontinuously at the er1tioal temperature.

Conduotivity measurements in the critical temperature reglon were

reported by E9'erahe1m. (75), as well 8.8 dielectric constant measure­ ments ('16).

Because ot ita theoretical implications , mantion

should be made at this point ot the critical opaleacence, which has

been the subject ot muCh controversy_ Tb& opalescence occurs when the system. is heat.d close to the critical temperature and is at

tirst limited to the phase boundary. It the sy-stem is kept at one tem.perature long enough, or shaken, or stirred, the opalescence

finally occupies the whole volume. On heating ...11 above the

oritical temperature the opalescence disappears but reappears on subsequent cooling, becoming Tery intense just betore condensation.

The moat generally accepted explanation is that developed by

Smolucho..ski (24) :from the Kinstein theory ot density fluctuations, and that ot Kaiater (25) which is essentially the same and attrib­ utes the etfects to statistical variations in density among the phase cells ot 'the highly compressed system. as a consequence ot the

41~tribut1on ot the velocity of the molecules. Donnan (26) in 1904 advanced an explanation for the opalesoence efrect on the basis of the intertacial tension or liquid drope at the critical temperature.

Lt the critical temperature the intertacial tension becomes zero tor all ordinary radii ot curvature but remains positive for small values or the radius ot ourvature. Henoe minute droplets ot liquid particles can exist tor a tinite range above the critical temperature. -'1­

'l'b.1s theory was supported more recently by Ostwald (2'1) who con­ aiders the critical opalesoence as a typical colloidal phenomena with liquid groups the dispersed phase. Similar theories ot dis­ persed liquid droplets .ere aleo advanced py J.ltsohul (28),

'l'.ra.vers and Usher .( 29) and Cardoso (30). According to Schroer (31) the pheulHDOn can be considered to be due to the superimposed ettecta ot both the Donnan and Smoluchowsld. "theories. DS.m8l.y, the emulsion ettect 1Ih1ch appears due to a premature :mixing ot the two phases betore their true mixing point and also a light dispersion ettect caused by 8tatistical tluctuations ot density.

In 1931 the attention ot this laboratory was drawn to a study ot critical temperature phenomena by the observatioa by

Sutherland and Maus (32) that the reaction velocity ot the hydro­ gen chloride-propylene system dropped to z.ero above the critical temperature, in spite ot the tact that the concentrations ot the reactants .ere as great or greater than the concentrations in the liquid state. In vie. ot this result a thorough investigation 0'1 the changes occur1ng at the critical temperature was undertaken.

Abr1et survey ot theae researohes tollows.

By the use ot a McBain-Bakr (33) spiral and a small glass float, Tapp, ateacie and Maass (M) were able to make accurate density measurements ot both phases at the critical temperature. The resulta showed conclusively that a sharp density diacontinuity at the critical temperature was obtained at the point where the meniscus diaappeared. Mecban1cal stirring tailed to destroy the discontinuity. Further density measurements .ere carried out by Winkler and Maass (~). Geddes and Maass (36) and McIntosh and Jlaass (7'). allot which confirmed the pers1s:tence

01' the 11quid above the crttlcal. temperature. It was observed

moreover that the magnitude of the denslty dltference, and the

temperature required tor equalization 01' the denslty was oharacter­ latic ot the aubstance under investigation. Once destroyed the den­

s1ty ditterence did not reappear on cooling until the liquid phase

retomed, • Time lags in the denalty were observed subsequent to

changes in temperature, and the lag was apparentl1' greater when the

system was being cooled above the critical temperature tban when a

corresponding heating waa carried out. Impurities such as air were

found to :magnify the denaity ditferenc••

A:.number ot oth.r physical properties ha.... been measured

in the crttical temp.ratur. region and in general these measurements

prortde turther evidence ot a discontinuity. Among the properties

inv.stigated ...re surface tension (~l. dielectric constant (38),

adsorption (39,40), h.a10 capacity (41,42). viscosity (43,44) t

opaleacence (45) and solubility (46). In addition P-V-T relation­

ships haVt been determined tOl" ethylene (47). !he P-V isothermal.

obtained indicated f'airly conclusively that (t~)T\O at the critical

temperature as required by classical. theory, but becames equal to o zero at 0.30 C above the critical temperature. ntis led to the

conclusion that a two phe.ae sya1o_ existed abovs the criticalt$elperature.

Considering now more particularly the theoretical

aspect of the general results outlined above, the classical theory

01' conttnui101 ot state cannot account tor the cr1tical phenomena observec1. In apite ot much pertinent crtt1cism ot the experimental

:methods employed to demonstrate the 41sconttnuity at the cr1tical -9­ temperature. nevertheless in View ot the many experiments quoted abo•• and espectally the work carried out more recenttly in this laboratory, the evidence in. tevor ot a discontinuity at the or!tical temperature is very ample.

To date, the hypothesis advanced by Maass (48) has been 'the BIOst satistactory in attempting to explain the critical phenomena obeerTed; liquid moleoules are postulated to be subject to a regional-onen-u.Uon, and in this respect a liquid ditters trom a highly compressed gas. 'I'he orientation must be coneidered dynamic in nature. as opposed to the orderly tixed arrangement in a crystal lattice. The liquid molecules are pictured as retaining their indiVidual translatory and rotational motions, but throughout the liquid there will be regions in which the molecules on the average assume certain preterred directiona. These regions are not sharply detined, blending into one another. and due to ordinary theJ!m8.l motions ot the molecules. these regions are continuously shifting, disappearing, and new ones tor.ming at new centers. This interpretation assigns to the liquid state a detinite structure as opposed to a gas which has no struoture. In this respeot the liquid atate represents an(: inte:rmediate stage, with the gaseous and solid states representing the extremes ot lack ot structure and a very pronounced and orderly structure.

The hypothesie ot a liquid "structure" has gained considerable support trom a study ot the mesomorphic state, more commonly called -liquid' crystals". The properties exhibited by substances 11ke cholesteryl benzoate, melting sharply to tom a milky anisotropiC liquid (mesomorphic state) and at a higher temperature undergping a sharp transition to a clear liquid, are well known. and have been sucaesstu.ll.y explained on the basis ot regional orientation.(See tor example :friedal (49) and Oseen (l5O). -10­

Evidence ot a liquid ·structure- has also been obtained tram. Xi-ray studies ot llquids. It baa frequently been ahown (51) that X-ray dittraction intenaity curves observed tor liquids closely resemble the smoo"-hed out curve ot the corr8apoJlding aolt4.

Stewart and co-workers (52) ha....e obtained X-ray patterns tor ethyl ether and iao-pentane in the critical resion. They expla1n their tindiD.ga in tems of a atructure in the llquid state which they call ·cybotaxia " •

The liquid state is conaidered to be composed of regions in which the molecules possess mutual orientation separated by regions in which the molecui_ are distributed at raa4om. The un1ta ot structure are called "cybotactic groups" and are belle....ed to in"t'Ol....e 25 to 1000 molecules each. This hypothesis has :much in common. nth that ot regional orientation described above.

It should be noted however that the :X-ray curves tor liquids can be explained without presupposing the existence ot any structure involTing an ordered grouping ot molecules (53,54,55).

'l'hua Harvey (55) tound that nitrogen under moderate preasure tar remo....ed tram the liquid state yields a dittraction pattern, and conclUded that to obtain a peak in the intens1ty CurTe 1t 1s sufficient merely to have a large number ot sca.ttsring centers in a small apace.

Numerous investigators ha....e developed theories ot the liquid state bued on theoretical conalderations. Sbaposh:D.1kov (56) computed a aeries of tables trom wl:Iich he cla1ma that the meniscus disappears when the liquid and vapor beoome misolble, which ocours when the densities ot the two phases are still ditferent. Muller (57) believes all substances except hellum contain polymerized molecules. -ll-

This "tie. is shared by Walker (58). Parthasarathy (59) obtained

endence to abo. that liquids contain aggregates of molecules not

in the nature of aaaociation. Important contribution. to this tield haye also been made by Debl" d(60), Eyring (51), Wheeler (52) and others.

1he methods of stat.istical mechanics have recently been applied with considerable success to the problem ot gas-liquid systUis.

Mayer and Harrison (63) by developing the ordinary st.atistical and thermodynamical equations of an tmperte~t gas, ahowed that these equations IDa) be extended to include a condensed phase. llolecular interaction is considered in tems ot cluster tormation dependent on intermolecular distance. The equations led to the usual condensation. phenomena and predicted the tollowing behaVior at the critical tempBrature:a"'Dlere are two characteristic temperatures, To and 1m, with Tc)'lm. Above To the P-V curve 1s nowhere horizontal and there exists no d1fterence between gaa and liquid. Below 1m the condensed phase has & surtace tenaion. Beween 'lm and 'l'c, and above To there exists DO surface tension". Ahove Tc, there 1s no Tolume tor which

(~~)T1S z.ro. Above ~ temperature ot cl1sappearance of the meniscus

('lm) a denaity diacoJltinui,y is pred1cted. The authors belleve the latter theoret1oal prediction to be em.ply eontir.med by the experimental resulu of Maass and CG-lIOrkera described a.bove.

Band (54) also on the basis at statistical mechanics has treated the condensing system trom the standpoint at dissociation ot assemblies. Thus,due to gas impertection molecules to~ clusters, and the cluster dissociates when the molecules moye out at the range at molecular torces. Condensation is treated as a clustering process. ~e principle theoretical deductions are summed up in the tollowing quotations: "The presence of considerable proportions ot very large clusters in the assembly under cond1tions close to the critical point, gives rise to a dependence upon gravitational potential which hitherto has been entirely neglected in the theory. At temperatures well below the critical only very small clusters in low ooncentration are to be expected a; the intertace,and the transition trom vapor to liquid is exceedingly sharp. But as the temperature approaches the critical large clusters(107molecules or larger)occur,and there w111 be an appreciable gradient ot ooncentration among these clustem ius to the etfect of sr&yity. !hi. gradie:n:i in concentration ot clusters is physically obaervable as the blurrinc ot the lIl8Discus, and occurs when there i8 ati11 a difference in density ot the two phases".

-,lcoorcling ~ our present argument the usually obaerved critical temperature at which the meniscus appears to Yaniah is somewhat too low; the true critical point will be where the difference in density Yanishes. 1he blurring ot the meniscus could theoretically be made to occur simultaneously with the true critical conditions onlY by making the observations in an arrangement which neutral.i.zea. the gravitational tield". Band baa further shown theoretically that although surface tension vanishes at To, the surface energy of large clusters. remains finite. 'lllis theory while derived in a ditterent way i8 in essence similar to that ot Mayer and Harrison, but ditfers in asa1gning the density di8continuities at the critical temperature to the gravitational field. II. PURPOSE OF 'fB:E INVES'liGATION

From. what baa be_ said aboye it will haYe become

apparent that, apart from the interest in the cr:ltical pbeaomeua as such, eritical temperature studies haYe yielded much i!lto:l'ma:;ion on

the Batura ot the liquid atate. In general terms. the present inYest­

igation ia an attempt to extend thia infozmation.

hctpt tor the work ot Winkler and Maasa (65) in which

the "1JIO-C01DpOnent systems comprised of propylene. methy'l ether and

carbon dioxide were lnYes"iga:ted, all ot the cr:ltical "em.pera"ure i studies in ,,~ laboratory haYe been oarried out with a one componen"

SY8".. In order to de"e:rm1ne whe"her the UJD8 general phenomena obaerved with a one component system could be ob"ained, or whether the introduction ot a second component modifiea the na"ure ot the phenomena. .. atudy ot the behaYior ot a two-coaponen" sya"em. in the critical temperature region was considered 1IOrthfttle.

J.part t:rom. the phase denaities. the phase equilibria. or phase compositions are the lJX)8" important physical properties ot a two c*mponent system in the critical tempera"ure region, and a detailed investigation ot these properties waa undertaken. It fta originally intended to obtain further intozmation on the same BYS"em. by carrying out P-V-T measuremente. This would haYe enabled the calculation ot the thermodynamic propertie. ot the system. However, because of the present war, this research program was interrupted, and to date only the phase densi"y and phase composition ot the system. eth1lene-propylene. have been determined. -14.­

III. GEN:li:RAL INTRODUC1!ION

Ethylene and propylene were cbosen as the two components to be studied. The reasons tor this choice are several.:

(1) Propylene has a small dipole moment while that ot el5hylene i8 zero. 'Ih1s ditterence 1n the nature ot the two molecules may have a con­

8iderable influence oa the equilibria obtained.

(ii) Mixtures ot ethylene and propylene yield a conTenient critical temperature and critical pressure.

(i1i) 'lhese gases are readily obtained in a pure state.

'!he crttical properties ot ethylene and propylene are

81IIIIIlr1zed in 'fable I.

Table 1.- The Critical Properties ot Ethylene and Propylene.

T d Reterence c c

Ethylene 9.2°0 (9.~C) 50.9 a~. 0.22 glcc (71, 92)

Propylene 91.40 C 45.4~a~ 0.233 glee (93)

The experiments were cont1ned throughout to an equi-molar system, that 1s, a system. containing ethylene and propylene by volume in the ratio ot 1:1.

Recently cona1derable interest 1n the phase - equi11bria ot hydrocarbon systems has been stimulated by the increasing tendency in present-day industr1al practice to subject hydrocarbon mixtures to conditiona ot temperature and pressure approaching ot exceeding the cr!.tical values. The ordinary laws ot solution and vapor pressure break down completely in this region, and necessitates an independent determination tor every sys~ to obtain exact thermodynamic data.

Up to the present time phase equilibrium data on a number ot binary hydrocarbon systems have been reported: sage, Lacey and eo-workers have investigated the methane-propane (66) t methane-e'tbane, propane­ n-butane, propane-n-pentane, methane-n-butane and methane-decane systems over a range ot temperatures and pressures including the critical. CummiD.gJ:I (67) obtained data trom atmospheric pressure through the critical region on three systems: n-butane-n-hexane, n-pentane-n-heptane and n-hexane-n-octane. Kay (68) studied the ethane­ heptane system oyer a pressure range including the critical. Ihase equilibria data tor the ethylene-propylene system has not appeared in the literature.

It should be pOinted out that it a discontinuity in phase composition at the critical temperature exists, the phase equi­ libria studies on binary hydrocarbon systems mentioned above, due to the methods employed are not capable of detecting such a discontinuity.

In every case a mixture ot the two components in knon. amounts was prepared, and P-V-T data were obtained on this mixture. For a binary system it has been general.ly Msumed that the two phases become uniform in composition at the critical temperature, but in fact this generalization has never been subjected to an actual experimental test. -16­

IV. EXPERIMENTAL:

a) Apparatus

In order to study the composition ot the two phases ot the syateIn in the crttical temperature region, it was neceasary to obtain a representative sample ot each phase in such a way that the equilibrium ot the system 1s not disturbed. 'lb1s was accomplished with the aid ot mercury contained in two amallaample bombs attached to a main central bomb. The mercury was allowed to tlow trom. the sample bombs into the main bomb, which displaced a portion of' each phase without changing the volume ot the aystem. The apparatus employed was similar in principle to that used in this laboratory by Holder and :Maaas (46). knew assembly was conatru.cted which embodied several modif'icationa over that ot the f'ormer apparatus.

i) Description ot the Equillbrium Bomb Fig.I ahows a cross section ot the main teatures ot the apparatus. It consists of' a central main bomb to whioh two small sample bombs B and a, are attached. The sample bombs are tilled with mercury at the beginning ot the experiment, and in order to withdraw a sample trom. either ot the phases, the valves ot the sample bombs are apened.

'!he mercury tlows into "he bottom. ot the main bomb and at the same time a portion ot the phase is drawn into the sample bomb.

'lb.e main bomb was machined trom a bar ot stainless steel (18-8 composition, "Sta-brite"). 'lhie material was chosen because it was tound that the phosphor bronze bomb employed by Holder and Maass (46) was slowly attacked by mercury. Moreover phosphor bronze has not a sufticiently high tensile strength, and threads cut into it at the joints yielded on tightening the gland nut at these joints. The stainless steel B

FIG. 1 - The Equilibrium Bomb . -17­ used is non-magnetic, which made possible the use of en eleotro­ magnetic stirrer.

'!he dimensions 01' the bomb were chosen so as to provide a sufticient depth in order that the meroury will run readily out

01' the sample bombs. '!he depth 01' the bomb was 11 in. and the inside diameter ~ in. with a wall thickness 01' i in. At the top 01' the 16 bomb a ahoulder was lettto~ which the sample bombs could be joined, and above this a tlange 4t in. in diameter to which the cover could be bolted. 'lb.e cover was 1 in. thick and was tastened to the bomb by means of four 3/8 in. steel bolts. Jl. lead gasket G was held in plaoe by two "V" grooves on the seat of the bomb, and by two try. shaped tongues on the cover.

'!he sample bomb. proper, B and C, were made 01' cold rolled steel. 'lhese units were the same as used by Holder and l4aass (46), and consisted ot a reservoir and a needle valve combined in a single body. The bottom 01' the reservoir consisted 01' a threaded plUg screwed against an internal shoulder. This shoulder defines the volume of the sample bomb. Seamless steel tubing was connected internally to the bottom plug by welding, and both the plug and tubing were re111roroed externally by silver soldering. No material subject to amalgamation comes in contact with the interior. The needle valves E and K, together with the needle valves F and D define the volume of the sample taken. 'Ihe needle valves, made 01' stainless steel, were

~eaded into the two bodies 01' the sample bombs, a tight closure, being ettected by means 01' a thin copper gasket. Graphite and string were used for the valve packings.

'!he bottom or liquid sample was drawn into the sample bomb C with the aid 01' a tine stainless steel tube T, which extends -18­ approx1.ma.tely two thirds ot the distance do1Rl. the main bomb. '!he plug

P merely served to reduce the unavoidable dead space at this point.

'!he stirrer S consisted ot a glass--encased iron core wi th sturdy glass sp1rals joined to aither end. A. bulb about 5/8 in. in diameter was joined at ths top end with the double purpose ot steadying the stirrer in .ts up and down motion, and 01' setting up a turbulanca in the vapor phase to ensure etticient mixing. ']he stirrer was operated by the solonoid H. which consisted 01' 3000 turns ot 1/20 B&S. cotton--covered copper wire, and which was connected in series with a make and break circuit. 1b.e aolonoid was enclosed in a brass case, and had a sufticiently large inside diameter {9cm) 80 that no temperature gradient would be set up along the length 01' the

Jamb as a result 01' any heating 01' the solonoid.

'!he design. 01' the equilibrium bomb is such that when the aolonoid is removed. the bottom ot the bomb could be surrounded with a Dewar tlask containing liquid air 1I1thout danger ot leak or ham to the bomb. This greatly tacilitated charging the bomb with the gases to be stud1ed.

2) The 'l'hermostat:

The thermostat consisted ot a cylindrical copper tank, titted .with two windows. and equipped wi th two high speed, tour-blade stirrers. A. high boiling hydrocarbon oil ()(arcol HX) was used as the thermostat liquid. Heating as well as regulation ot the thermostat was ettected by a single, inter.mittent 250-watt heater placed halt­ way down the side 01' the bath. By supplying heat to the thermostat intermittently in this manner, and operating the stirrers at a high speed, temperature gradients were eliminated. Although slight heating

01' the solonoid, which operated the bomb stirrer, did occur, this .FIG. 2 - Ana lytical APPA· aratus. -19­ was efficiently dissipated by the brass case enclosing the solonoid.

'Ihe:rmocouples were placed at various points in the thermostat, end no temperature gradients could be detected either in the bath itself. or around the solonoid and along the length of the equil1brium bomb. o Temperature control was good to :to.Ol C. The thermometer used througbout 118.8 previously calibrated against a pla't1num. resistance thexmom.eter.

3) .Analytical. Apparatus The essen't1al features ot the analytical apparatus are shom in Fig.2. III is a conste.nt--volume manomater equipped with a mirror scale. The calibrated l2--11tre volumes A and B were used for storing purified ethylene and propylene respectively. 0 and

D are two calibrated 3-l1tre volumes into which the liquid and vapor samples trom the equi11brium bomb were expanded. Ethylene and propylene are contained in the cy11nders G. The bulbs F and E were used tor purification of' the gases. The bulb I, made of heavy walled pyrex tubing, tree from stratns and striations was used for deter­ mining the critical temperature and the critical density ot the ethylene--propylene mixture. H is a calibrated 500 cubic oentimeter volume in which the gases were measured in t1lling the bulb:\ I.

'!he e,uillbrium bomb 118.8 joined to the apparatus at

J' by means of a p1ece of copper tub1ng. which in tum 1118.& connected to the glue tubing by a de Khotinaky joint. P is a 'lbep1er pump;

S is a 1ow--tanperature analytical fractionating co1umn of the

Podbiel.D1ak type (70), equipped with a column manometer Me and a receiver manometer 15. 1he receiver R had a capaoity of 600 cubic centimeters. -20­

b) Material.a

Ethylene and propylene were obtained f'rom the Ohio

Chemical Co. 'Jhe ethylene gas was certif'ied 99.5% pure, and the propylene 99.~ pure. The gases were condensed separately in the bulbs E and F and wb.1.1e surrounded with liquid air vacuum was applied to remove any permanent gases. J'ach gas was then f'raction­ ated once, the tirst third and last th1rd f'ractions being discarded.

'lhe middle tractions were stored in the volumes A and B.

c) Procedure.

i) PrePAl'tion for an'Exper1ment Into the equilibrioa bomb 40 cubic centimeters ot mercury were placed. 'l'b.e cover was then bolted on, and the bomb connected to the analytical apparatus (Fig.2). The needle val.vtle on the sample bomb B were opened, while the valves ot sample bomb

C were closed. The system. was then ,"acuated. Valve D was closed, and ethylene or propylene was admitted to the apparatus to a pressure of' one and a half' atmospheres. f'orcing mercury up through val.ve E and f'illing the reservoir B. Val.ve E was then clos8d.

Sample bomb 0 was f'illed with mercury in the same manner. When both side bombs were :tilled, enough mercuq remained in the main bomb to cover "the bottom. The apparatus 118.8 then again thoroughly evacuated and f'lushed tWice with propylene or ethylene. All evacuations were carried out to a pressure of' 1)(10-4 to 10..5D1D.. of' mercury.

2) Fill.1ng the Equilibrium Bomb

The volume of' the equilibrium bomb, when it was ready 'to be charged, (1,e. when the sample bombs were t1lled and a l1ttle mercury remained in the bottom of' the bomb) was cal1brated -21­ by weighing with mercury. This volume was tound to be 87.43co.

The amounts ot ethylene and propylene required to g1ve a 1:1 mixture and a mass--volume ratio ot 0.230 were calculated, and condensed into the bomb with liquid air, propylene being oondensed tirst. The amount ot each gas condensed was measured accurately. by the ohange in pressure intthe calibrated volume A, (ng.2) both gases being measured sucoessively f'rom the same volume. 'lhe aocur­ acy with which the amounts of' the two gases were measured were thus dependent on the pressure measurements only. Pressures were read to

O.lBm of' mercury. Since the amounts ot propylene and ethylene used were of' the order of' 12 grams and 8 grams respectively, the error in the measurement ot the masses ot the gases condensed into the bomb is believed to be considerably less than 0.1%.

The charged bomb was placed in the thermostat at the desired temperature and the stirrer started. Thermostating was continued f'or 14 hours or longer with continuous stirring, to allow the system to come to equilibrium. The rate ot stirring varied f'rom

75 to 120 strokes per minute ( a stroke including one up and down

motion ot the stirrerl. Between these l1m1 ts the tinal equil1brium obtained was apparently independent ot the rate ot stirring.

S) Sampling

In withdrawing the phase samples, that ot the

-liquid- or lower phase was taken tirst. ValTea F and K (Fig.l) were opened f'or a suf'f'1cient time f'or the meroury to run down into the main bomb. In the same way the vapor or upper semple was then drawn into the sample bomb B by opening Talves D and E. The apparatus was removed trom the thermostat and after the pressure in the main bomb had been released. was joined to the analytical apparatus (1I"1g.2) at -22­

1 J and evacuated. 'lbe samples were then expanded into the calibrated

volumes a and D and the pressures and temperature recorded. By means ot the 'l'oepler pump P the sample bombs could be pumped down to a

pressure ot lam ot mercury. and the gas samples in the volumes C and

D could be circulated to ensure proper mixing.

4) Anal.lsis ot the Samples The 88lllPles ....rca analysed by lo1lE-tem.perature traction­

atlon. 'Ihe tractionating column was ot the Podb1eWalt type ('10). A 500cc. portion ot the phase semple was transterred to the still by means ot the Toepler pump P )F:lg.2) and condensed In the bottom ot the

column. Ethylene was distilled over 1n the usual manner and the

reeeiver pressure recorded at the out point. 'lb.e propylene was then

allowed to expand into the same receiver, and the tinal pressure

reoorded. The composItion ot the sample in mol perctnt (or volume

percent) ot each component could then be ealculated direotly from the pressure readings of the reoeiver manometer. Duplicate analyses ot the

phase sample. were made.

In order to establial the accuraoy that could be attained by the analysis, as well as to improve the analytical tech­ nique, a number of synthetic samples were prepared and analysed. 'lhese contained appro:rlita.tely equal amounta by volume ot ethylene and propy­ lene, corresponding to the proportion ot ethylene and propylene which will be encountered in the phase equilibria experiments. A comparison ot the composition of tka some synthetic samples, and the oomposition determined by analysis after the technique had been well developed is

shea iJi Table II. -23­

Table 11- Analyses of Synthetic Mixtures of Ethylene and Propylene Gom;22si tion iMole ;eer coti - Deviation S~th.tic SamR1I BZ Anallsis ~ (Mole per cent Error % Ethzlene Pro&lene E,hXJellja iPg.ypy1ene Etllllene) 48.35 51.65 48.44 51.56 0.09 0.18

48.73 51.27 48.7'1 51.23 0.04 0.08

50.19 49.81 50.14 49.86 0.05 0.10 50.55 49.45 50.5'1 49.43 0.02 0.04

51.23 48.'1'1 51.16 48.84 0.0'1 0.14

Tne accuracy claimed by Podb1elniak for analysiS by this

method is of the order of 0.5%. According to the above results an

accuracy of the order of 0.2% bas been achieved. This is to be expected however since only the two constituents are present, and these in nearly equal amounts, thus greatly simplifying the analysis.

'!he agreement in duplicate analyses of the actual phase samples however was not always quite as gpod, due probably to the detailed manipulation and handling of the samples involved. d) Results 1) Oritical Temperature and Critical Density of a 1:1 Ethylene--Pro;eylene Mixture Before any measurements of the phase equilibria of the system in the critical region could be carried out, it was necessary to determine the critical temperature and the critical

density of the system. This was accomplished by filling glass bombs

to various densities and observing the temperature of meniscus d1&­ appearance as the bomb is gradually heated; for a critical filling of the bomb, the meniscus disappears near the centre of the bomb. The glass bombs were blown from high pressure pyrex -24­ tubing whioh had an inside diameter of 10 mm. and a wall thickness of 3 rom. Capillary tubing 1 mm in inside diameter was sealed to one end by means of whioh the bulb could be sealed to the analytical apparatus (Bulb I, Jig.2). A small stirrer oonsisting of a glass enoased iron oore, joined to a glass spiral was enolosed in the bomb by means of which the medium could be electromagnetically stirred in a manner similar to that of the steel equilibrium bomb. The volume ot the bombs, which ~aried from 5.8 cc. to 6.8 c.c., was determdned by weighing with mercury. Because of the pronounced effects of small amounts of impurities on the critical temperature, the gases were carefully purified as desoribed above. and the bombs evacuated to a pressure of lXlO 5 rom of mercury and flushed several times with propylene or ethylene.

By means of a oapillary stopcock: joined ddractly to the bomb (Fig.2) the two gases could be measured and oondensed successively; was propyleneftcondensed first. The gases condensed were accurately measured be the drop in pressure in,the calibrated 500 c.c. volume H(Fig.2), which was immersed in'a water bath. In this manner the bombs could be tilled to any desired density. ~e bmmbs were sealed otf immediately below the stopoook and allowed to warm up to room temperature and subsequently placed in the thermostat at a temperature close to the critical. The temperature ot the thermostat was gradually raised (about O.loC per hour) and the meniscus behavior observed. Beoause the preliminary experiments on phase equilibria were to be carried out witho.t stirring of the medium. the tirst measurements ot the were made critioal tsmperature in the glass bOmbS ii~nout stirring. The results ,A -25­ are summarized in Table III.

Table III- Critical Temperature and Critical Density ot 1:1 Ethylene-Propylene .Mixture

Temperature ,I5C~ at which meniscus Position ot Density Became Disappeared Reappeared meniscus at critical OE!;lescent tem:2erature 0.220 57.67 58.60 58.24 Below centre

0.230 57.67 58.40 57.90 M1.ddleof'bulb

0.230 57.79 58.44 58.00 Middle of' bulb

Due to the peculiar behavior of' the meniscus it was difficult to state detinitely when the meniscus had disappeared, as it broadened out into an opalescent disc. which gradually became more ditfuse. ~e temperature at which the ppalescence appeared was however quite sharp, as was also the temperature of' reappearance of' the meniscus. The cr1tical density was tak en as 0.230.

'nle critical temperature when the medium is stirred is a more definable quantity and can be accurately reproduced. 'lbe temper­ ature at which last traces of' liquid disappear is def'inite. It was f' tound however that the maximum temperature at which liquid can exist varies considerably with the mass--voluma ratio ot the bomb tilling. 'lbe results of' a number of' experiments are shown in Table IV and plotted in F1g.~. ., r--- -,------r----,-----,

ro r----r---4---+---~

~ r---+---~-~

., ~-_~ __~~~_L-__~ 0 . 18 0 .20 0 . 22 . 0 0 . 24 0 . 26 MA.SS - VOLl.l&! ~1I O . GII. ./C.C.

FIG. 3 - Relation or the Critical Temperature

to the Mass - Volume Ratio. -26­

Table IV- Relation of Oritical Tamperature to the Mass--Volume

Batio, with stirring of the medium.

Mass-Volume Ratio ~erature ot 41s­ 0 Posltion of meniscus (gmJe.c.) appearance of liquid( C) disappearance

0.190 59.89 Bottom

0.200 59.56 It

0.200 59.59 .. 0.210 59.25 .. 0.220 58.70 ..

0.220 58.74 It

0.225 58.48 Below middle

0.230 58.27 Middle

0.230 58.31 ..

0.250 58.29 It

0.250 58.31 It

0.240 57.94 Top

0.250 57.59 tt

It was observed that for a maBa--volume ratio less than

0.250, the meniscus remained more or less stationary until a few tenths of a degree before the liquid disappearance, when it gradua1ly moved

to the bottom of the bulb and disappeared. On lowering the temperature again the first traces of liquid appeared at the bottom. The temperature of disappearance and reappearance ot liquid was found to co1ncide

111 thin O.Oloe, and indicates therefore a true equilibrium, which cannot be attained without stirring. These results are in agreement with the experiments of Mason, Naldrett and Masss (74) using a shaking bomb. -27­

Wi thout stirring or sheldng, the temperature ot meniscus reappearance is usually somewhat lower than the temperature ot meniscus disappearance as shown by the results ot 'lable Ill. and which has been the general experience in this laboratory.

J"or a mass-volume ratio greater than 0.230, the meniscus rose and disappeared atl the top ot the bulb aa the temperature was raised. I'or a tilling ot 0.230 alone, the meniscua remained stationary until it disappeared at the oentre ot the bulb, and this was there­ tore taken as the critical density. The temperature ot liquid dis­ appearance. corresponding to this density. 58.30o±O.O~C. ftS taken as the oritical temperature ot the mixture.

It is of interest to compare the behavior ot a two­ cwnponent system with that ot a one-component system in the critical temperature region. In a one-component system, the critical density represents the maximum ot the classical, parabolio vapor-liquid co­ existenoe curve. In a two-component system, the critical density is not the maxhmm ot the vapor-liquid ao-e:D.stence curve, but, as was early observed by Kuenen (78). and as illustrated by Fig.3. the maximua ot this curve lies at a density considerably less than the critical. Moreover in a. one-component system, critical phenomena can be observed over a. considerable range ot densities t whereas in a two-component s1stem as exemplified by the ethylene-proP11ene system ('lable IV) t critical phenomena occur only over a rather limited density range.

Due to this lim1ted cr1tical denait1 range, and because it ft. necessary to have the meniscus disappear in the centre of the equilibrium bomb so that a true phase sampling would be ob~a1ned near the oritical tanperature, the experiments on phase

equilibria were confined to a density of 0.230, which has been

shown to be the orttical dellSity for the mixture under investigation.

2)Results ot Phase Equilibria MeaaU1'tlDl81lts wi~hout

stirring of the System.:

Some prel1m1nary experiments were carried out in

which ~he medium in the equiliijrium bomb was not stirred. The period

of thermostating varied from 8 to 12 hours.. The results of these

experiments are summarized in ~ble v.

Table V- Phase Equilibria in the Critical Temperature Region

ot a 1:1 Ethylene--Propylene Uixture without stirring.

Temperature Va~r Phase Lig.u1d Phase °c Density Composition Dens1ty Compos!tion (MOle ~ ethylene) (lllole " e~ylene) 56.95 O.ll '12.9 0.4:4 28.0

58.20 69.1 30.1

59.4:2 0.12 68.4 0.3'1 31.8

59.54 0.12 68.5 0.3& 31.4

63.23 0.13 65.1 0.36 34.4

!he phase denaities were calculated tram the known volumes of the aa:mple bombs, and the pressure, volume, temperature and composition (by analysis) of the expanded sample J and are include" in Table V. These experimente are to be considered as preliminary in nature, and no attempt 68 made to ~8tabllah to what extent the results represented a true equilibrium state.

They demonstrate however that without stirring or agitation of the system, a large difference both in composition and in density e:dsts between the upper and lower phase, even after prolonged thermostating. A.t the highest temperature studied, 58.2So0, the composition of the liquid and vapor phase still varied by 30 mole percent. Because ot the uncertainty ot establishment of eqUilibrium, and the prolonged thermostating periods which would no doubt be necessary under these conditiOns, it was considered ~perative at this point to study the phase equilihria of' the system with stirring during the period of' thermostat1ng.

S) Beauts ot Phase Equ1llbria .Meaaurementa with : stirring of the system

As mentioned above the exper1menta were conf'ined to a IIUs--TOlume ratioot 0.230, and to a m1:x:ture o'l ethylene and propylene in the ratio o'l 1:1. Stirring was carried out throughout the pertod of 1i.hermostating, and also while the samples were being withdrawn. '!he period of' thermostating varied 'from lS to 20 hours.

With the rate of stirring used, equilibrium. was probably reached in a considerably shorter tU-. It was found convenient however to ther­ mostat the equilibrium. bomb over--night.

'!he results of the phase equilibrium measurements are sUDlD8.rized in Table VI. 'lb.e tirst colUIIID. g1ves an indication of the order in which the runs were carried out. The tollowing nomsn­ clature has been employed in summarizing the data tor the liquid and vapor phase:

Vv- volume of' expanded vapor phase sample. p v - pressure (om. > ot expanded vapor phase sample.

Tv - temperature (oe) ot expanded vapor phase sample.

Xv - composition ot vapor phase in mole percent ethylene. dv -- density of vapor phase in gm./cc. '!'able VI - Phase Equilibrium Data of' 1:1 Ethylene - Propylene System in the Critical Temperature Region

F!J::pt. T~. Val!2r Phase L1.g.uid Phase Pv"'P1 dy+d no. C d 1 Tv Pv Xv ~ Tl Pl xl 1 2­ ~------...------..--...... -..----.....------..-----.....-..------...-.....--, 1 58.68 21.'1 58.30 00.3- 0.226 21.7 50.'10 50.0 0.233- 119.00 0.230 2 58.43 22.5 59.9;5 50.1 0.200 22.5 60.35 49.9 0.23-2 120.30 0.231

12 58.38 22.1 59.90 50.4 0.200 22.1 60.50 50.1 0.232 120.40 0.231

'1 58.34 50.2 22.5 60.30 50.2 0.232

3 58.28 21.2 53.50 50.'1 0.20"1 21.2 66.25 49.4 0.257 119.85 0.232

5 58.12 22.4 50.61 51.5 0.194 22.4 68.85 48.8 0.268 119.45 0.231

*11 58.14 22.0 51.19 51.3 0.195 22.0 68.40 48.9 0.256 119.59 0.231

8 5'1.6'1 20.0 47.25 51.8 0.182 20.0 '12.30 48.2 0.284 119.55 0.233 14 57.57 22.1 47.52 52.2 0.182 22.1 71.50 48.1 0.279 119.12 0.230

4 5'1.00 22.0 44.80 53.0 0.168 22.0 74.15 4'1.5 0.290 118.95 0.229

9 56.04 22.1 41.41 53.4 0.15'1 22.1 78.31 46.'1 0.307 119.'12 0.232

6 55.84 21.5 41.45 53.5 0.158 21.5 77.85 46.8 0.306 119.30 0.232 13 55.02 20.0 40.00 54.2 0.151 20.0 '19.16 46.3 0.313 119.16 0.232 10 54.13 21.5 38.40 54.5 0.142 21.5 81.50 45.9 0.321 119.90 0.232

o 0 * Temperature raised to 58.70 and kept oonstant f'or 12 hours,then lowered to 58.14 and thermostating continued f'or 13 hours. ..

T• ~-.....,c...... - ""...-.-- ... -... .-.. ----... ..f------+­ i L.

0.1:> 0." 0." OPXJITT . cat. /e.c .

FIG . 4 - Plot of Phase Densities in the

Critical Temperature Region. -30­

Vl - volume ot expanded liquid phase sample. Pl - pressure (em.) ot expanded liquid phase sample. Tl - temperature (oC) ot expanded liquid phase sample.

Xl - composition ot the liquid phase in mole percent ethylene.

dl -- density ot the liquid phase in sma/c•c •

The values ot Vv and Vl were obtained by calibration with water and were 3113.2c.c. and 3133.9c.c. respectively. From the VOlume, pressure, temperature and composition ot the expanded samples, and the volwne ot the sample bombs, the phase densities, dv and dl. were calculated. The yolumes ot the sample bombs were obtained by weighing with mercury, and were 15.43 c.e. and 15.40 o.c. tor the vapor and liquid samples respectively. It 1s dittioult to estimate the error ot the phase densities obtained in this way. The detailed manipulation ot the phase samples involved limits the aocuraoy with whioh these values can be determined.

Another serious diff1cul~y i8 the tailure occasionally ot the mercury to drain out of the sample bAmbs completely when the phase samples are being withdrawn. Nevertheless the error due to this oause was not as great as might be expected, a fact which is borne out by the near constancy of the SUlll PV+Pl in the second last column of Table VI. The last column ot the table represents the calculated average mass-­ volume ratio of the bomb tilling. These values ot course are subjeot to the same errors as those of the oaloulated liquid and vapor phase densities. but agree however reasonably well I'llth the value 0.230, the original mass--volume ratio of the bomb filling. This was found to be a valuable test for leaks in the bomb system.

In view ot the a.ove considerations, the phase densities T. ­ . ,-,..-.;...o...~ ------­ .. f-----t--­ o o

o ~ L.

FIG. 5 - Plot or Phase Composi tion in the

Critical Temperature Region. -31.­ tabulated in Table VI are to be considered as rair approximations of' the relative phase densities rather than absolute values. Fig.4 is a plot of' the ealculated phase.densities against temperature. The phase compositions of' the system through the critical. temperature region are shown in columns 5 and 9 tor the vapor and liquid phases respectively, and are plotted in Fig.5. A summary or the phaseequil1brium data taken f'rom Table VI is contained in Table VII.

Table VII - SUmmary of' Phase Equilibrium Date. of' 1:1 Ethylene--Propylene System in the Oritioal.­ Temperature Region.

T~. Va122r Phase Lig,uid Phase 00 dv Xv dl Xl

58.68 0.226 50.3 0.233 50.0

58.43 0.230 50.1 0.232 49.9

58.38 0.230 50.4 0.232 50.1 58.34 50.2 0.232 50.2

58.28 0.207 50.7 0.257 49.4

58.12 0.1.94 51.6 0.268 48.8 58.14 0.196 51.3 0.266 48.9

57.67 0.182 51.8 0.284 48.2 57.67 0.182 52.2 0.279 48.1

57.00 0.168 53.0 0.290 47.5

56.04 0.157 53.4 0.307 46.:1

55.84: 0.158 53.6 0.306 46.8

55.02 0.151 54.2 0.313 46.3

54.13 0.142 64.5 0.321 45.9 -32­

V. DISCUSSION OF Rl!SULm

'!he moat 1m.por'tant conclusion to be d.rawn. trom. the abo .... reaults ie the tact that no ditterence 1n coonpo81t10n ot the vapor, and What was the liquid phase, was detected at or above the critical temperature ot the 1O'8tem. !h.e crttical temperature ot the s;ystem 11'&8 determined to be 58.30°0:to.0500. A.t a temperatura ot OS.34oe and at higher tem.peratQ.l'e8. the compositiona ot the upper and lower phase are, within the limits ot experimental error, equal. lD support ot thie conclus10n aeveral releTant points merit discussion.

'lba:t the phase compos! tions obtained at each "temperatura represent *rue equilibrium oonditions there oan be l1ttle doubt. ~ time ot thermostatlng as well as the rate ot stirring used were ample to allow equilibrium to be attained. With the same rate ot stirring 1n the glus bombs, the liquid phase 11'&8 tound to appear and diaappear with1n a :range ot 0.01°0 at the critioal tempera.ura, 1ncl1.cat1n& a rap1d eatabl1ehment ot equi11brium under these cond1tions. J'inallJ', it has been demonstrated taee exp't, no.ll, 'l'able VI) that the aame equilibrium cond1't10n 1s obtained when the syatem ie tiret heated above the cr1t1oal temperature, as when 1t 1s brGught from. a lower temperature, and thermoetated at a gi....n temperatura; the .quilibrium is thus reveraible with reap.ct to temperature•

.An obvious er1"ttclam ot theae exper1m.ente i8 the 1nab111ty to obaerve the meniscus behaTior in the equilibrium bomb. 1Ih1le W. i. e .erious 41aadTantage, the et·tect it 11187 haTe on the present results will depend on the accuraoy with which the critical taapersture can be reprGduced. With slas. bombs the critical taperature has been shown to -33­ be quite reproducible. If i1t is assumed that the meniscus disappeared in the equilibrium bomb at a lower temperature than in the glass. bombs, as would be the case in the presence of impurities, then the results could still be 1nterpretated to indicate a differenoe in phase composition at the critical temperature. However it was possible to obtain fairly oonvincing evidence that liquid phase was present at o least u high as 58.28 C tram the sound of the glass stirrer moving up and down in the metal bom'ij. In the absenoe of liquid the noise or the stirrer, moVing up under the magnetic field and striking the bottom when the field was off, was somewhat muffled, while in the presence of liquid, the noise was particularly audible. By holding the ear close to the top metal support of the bomb a characteristic "swishing" of the liquid could be heard as it was being Vigorously stirred.

The behavior of a one component system in the critical temperature rEition has been explained by Maass and co-workers (48) by means of the hypothesis of regional orientation. Ltquid molecules are postulated to be subject to a regional orientation. 'nle liquid state is thus characterized by a definite structure. Experiment sboWfA-that at the crttical temperature a difference in density persisted between the upper and lower phase after the meniscus had disappeared, and could be explained by assuming that liquid struoture persists above the temperature of meniscus disappearance. This theory of liquid persistenoe has been further developed by Mayer and Harrison (63) and by Band (M) on the basis of statistical mechanics. and it has been shown that a clustering of molecules occurs at and slightly above the observed critical temperature. Same recent experiments in this ~

laboratory (44,4'1) indio:ated that a more adequate explanation ot the critical temperature phenomena is obtained it the persistent

liquid phase above the critical temperature is considered ~ become mutually dispersed to a greater or lesser extent with the

vapor phase. 'lhese theories can be extended to explain the behavior at the critical temperature of the two-component system studied in the present investigation.

As tor a one-component system in the critical temper­ ature region a persistence ot the liquid state may be postulated, where the liquid aggregates now are composed ot two-species of molecules. It is not unlikely that due to inherent differences in the two molecules (propylene possesses a dipole moment) one speCies of molecules may be capable ot UclusteringU to a greater degree, but since the two substances are mutually soluble in all proportions, the composition ot individual clusters will on the average be tm.1form and will be.i iependent on the temperature (and pressure). At the critical temperature, whers the liquid persists, the vapor phase may be expected to be richer in the more volatile component, ethylene, and the persistent liquid phase richer in the less volatile component, propylene. Due to this difference in phase composition, the ditterence in the phase densities will be enhanced, since the less volatile component hss slso a greater molecular weight. SUch a state of aftairs may be expected at the critical temperature ot a two-- component system in the absence of any stirring of agitation.

k'system !If in this state (that is without stirring) is exceedingly

difticult to investigate experimentally and the time for equilibrium

establishment may be expected to be considerably greater than in a -35­

one-component system, where, due to the high compressibility, true equilibrium is reached but slowly. If however the system at the oritical temperature is stirred or agitated a mutual dispersion ot the liquid olusters with the vapor molecules will

occur. (The liquid clusters referred to here must be thought of as dynamic groups which are continually breaking up and reforming). This mutual dispersion, although it ocours to a lesser extent slightly below the critical temperature where opalescence first appears, becomes complete at the critical temperature where the surface tension of the liquid is zero. Because the suftace tension is zero the dispersion is not in the aature of an emulsion. The dispersed molecular groups of clusters are considersd to be micro­ scopic in magnitude and because of this as well as their dynamic

structure, 11111 not settle at the bottom of the bomb when stirring is oeased, except perhaps a lesser concentration by the gravitational

field. As the temperature is raised above the critical temperature,

the molecular groups of clusters, due to the increased kinetic energy of the individual molecules, become disrupted, and finally a

true one-phase system is reached. There is "a priori" no reason to assume all the clusters or molecular groups to be of uniform microscopic size, and as a matter of fact such a state is highly 1mprobable from statistical considerations. If the presence of larger clusters, even to the extent where they assume macroscopic dimensions is postulated, a density discontinuity may be observed between the upper and lower part ot the system in spite of vigorous stirring.

However since the two components are mutually soluble in all pro­ portions, a density discontinuity does not demand a discontinuity in phase oanposition. Unfortunately this question could not be settled b. the present investigation. It will be observed that tirst in theAtour experiments ot Table VII, the vapor phase density 1s consistently slightly less than the liquid phase density, but the

ditterence lies within the range ot experimental error and a ietinite conclusion as to whether the difterence is real would be unwarranted. It is desired to point out however that a density discontinuity is not tlPossible, even though the phase compositions

are unitorm. 'lhis point :may mert t further investigation. The question ot whether a dispersed two phase system actually exists at the critical temperature where the oomposition of the upper and lower parts of the system become unifonn could also be settled by acouratemeasurements ot the P-V-T relationships immediately above the critical temperature. This prooedure has met with sucoess in this laboratory for a one component system, and the temperature at whl0ll(~C)T.:::::'0 was found to be O.70 C higher than the true critical

temperature (obtained b~ shaking or stirring the system), indicating a two phase system over a tinite temperature range above the critical temperature. -37­

SUMMARY

Phase equilibria measurements have been made tor a 1:1 ethylene--propylene system in the critioal temperature region by means ot an apparatus which enabled the withdrawal ot a phase sample trom the liquid and vapor phase without disturbing the equilibrium. ot the system. The critical temperature and the critical density ot the system were determined. The critical temp­ erature was tounc1 to vary with the mass-volume ratio ot the system. Analysis ot the phase samples showed that no discontinuity in phase composition occurs at the critical temperature whan the medutm is stirred. Approximate relative phase densities were oalculated trom the data obtained, and likewise, within the limits ot error, exhIbited no disoontinuity at the critical temperature. Without stirring the attainment ot equilibrium i8 s~ow and uncertain. me results are interpretated by means ot the liquid persistence and dispersion theories based on considerable experimental evidence in this laboratory. -38­

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OI..I.DB TO omGINAL WORK

In Part I an origin.al study of some chem1ca.1 warfare reagents is presanted. Cyanogen fluoride was prepared and its. properties investigated to deter.m1ne i'tis adaptabillty as a war gas. The solubility, toxicity and the service time for cyanogen fluoride were measured, and it was shown that the gaa does not poaseas any outstanding properties which would make it a Tery effectiTe war gas.

The service times for araine, phosgene, and phosphorous trifluoride were determined for a number of respirator charcoal samples by means of an apparatus which appro:x1laa.ted the behavior of the human lUD.g. All the impregnated charcoal samples submitted were shown to proTide fairly adequate protection against the gases studied.

An intensive atudy of the phase equilibria ot a two­ componen:t system in the critical temperature region has been made for the first time. '!he cr1tical density and the critical temperature of the system were determined. The critical density was shown to vary with the mass-volume ratio ot the system. It was turther demonstrated that when the medium i8 stirred no discontinuity in density or phase composition occurs at the critical temperature, while without stirring the attainment ot equilibrium is slow and uncertain.