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Bulletin of the Society of Scientific Photography of Japan, No. 4-5, Dec., 1955

STUDIES ON BLUE PRINT MATERIALS (Received Sept. 23,e 1954) Yoshitada TOMODA Government Chemical Industrial Research Institute, Tokyo

Introduction

It is said that the principle of blue print materials was first discovered by 3. Herschel in 1840 and since then the photochemical reactions of ferric salts were studied in Europe up to the earlier period of this century. The blue print materials play an important role even at the present time because of their simplicity and low price, but the fundamental studies of these materials from the standpoint of scientific photography have been rather neglected, even though patents or some devices were presented. Recently, senstometric studies of blue print are reported by Mr. A. Hnateko who carried out experiments on the intermittent effect or solarization of blue print, but unfortunately we cannot learn the results in detail. In this country, studies on this subject show activity and fundamental problems were discussed by Prof. Kameyama, Messrs. Kishida, Katagiri, Tsujimura and Suzuki2) in Tokyo University. Parallel with those fundamental studies, problems must be considered from practical point of view in order to contribute in some ways to the improvement of technique, and (in this meaning), photochemical properties such as sensitivity, contrast or blue densities are discussed principally in this report.

Experimental

Photographic properties of blue print materials will be reasonably discussed, if their characteristic curves are determined by the similar procedure as that used customary for silver halide materials. So in our experiments, using a grey optical wedge, test pieces of blue print paper were exposed to a mercury lamp under definite conditions, and then they were treated with an oxidizing bath such as 1 % bichromate solution. Then, after drying test pieces, blue densities were measured by Yamabe's densitometer applying the Wratten's red filter No. 26. The energy intensity of the light source was previously determined by a thermopile and as to the transparency of the optical wedge, it was corrected by photometric measurements. Thus, H & D curves of blue print were obtained for each test piece and they were taken as a basis of our whole discussion. [I] Formation of blue image. When light sensitive paper containing ferric ammonium and sodium ferricyanide is exposed to light, a blue substance will be formed and if the exposure is continued, the blue colour will soon be bleached. But the bleached print regains its colour on treatment with oxidizing agents. This character of blue print is shown by H & D curves in Fig. 1, where the curve I represents the formation of the blue substance during exposure which causes solarization due to bleaching and the curve II is the density curve of blue print oxidized by 2 % ammonium bichromate after the above- mentioned exposure. H & D curves were determined always taking blue densities as ordinate and log E abscissa where E is represented in erg/cm2. In the first stage of exposure, Turnbull's blue probably formed as the ferricyanide3). Thus, the reaction may be, 8 Y. TOMODA Bull . Soc. Sci. Phot. Japan

Fig. 1 H & D curves of blue print. I: exposure only II: exposed and oxidized

(1) (2) But the reaction product is not so simple and there may exist KFe++Fe+++3[Fe++(CN)E]3 or other complex salts. Here, we must pay attention to a decrease of blue densities after the bathing of the blue print as it is shown by the line A in Fig . 1. This means that, either a part blue substance formed in the earlier stage of exposure dissolves into the solution of oxidizing bath or it changes to a colourless substance by oxidation . It seems probable that the former case exists really and it may be reasonable to assume that soluble is formed partially in the course of reaction2) . Solarization of blue print is also an interesting behaviour and this is explained by formation of colourless ferrocyanide by photo-reduction4) , but the mechanism of reaction is discussed in many ways2)5), and a conclusion cannot be drawn easily without further experiments. However, this photo-reduced substance regains its colour by oxidation as shown by the line B of Fig. 1, and the blue colour formation is also observed after washing with water in place of the oxidizing bath , but colour formation is slow and image contrast is low in this case , so the use of the oxidizing bath is practically desirable and 1 % ammonium bichromate solution showed good results but raising the concentration of bichromate was ineffective. The density curves in Fig. 1 are a result of blue print exposed 3 minutes , and we carried out in the same way a series of tests exposing 30 seconds , 1, 2, 3, 5 or 7 minutes, and obtained H & D curves which cannot be put one upon another because the increase of both blue density and contrast was accompained with elongation of exposure time . This means that the reciprocity law failure exists for blue print paper as in the case

Fig. 2 Reciprocity curves of blue print. No. 4-5, Dec., 1955 BLLTE PRINT MATERIALS 9

of silver halide emulsion. Rearranging our results, we obtained Fig. 2 which shows the fact. These are equidepsity curves of differently exposed blue prints and considerable deviation from the reciprocity law is confirmed.

[II] Concentration of sensitive solutions. When we prepare blue print paper, its quality depends largely upon the composition of sensitive solutions especially upon their concentration. Here, keeping the ratio of each component as constant, we examined the influence of concentration on H & D curves of blue print. Composition of solutions was as follows : ferric 12 g. sodium oxalate 0.75 g. sodium ferricyanide 2 g. ammonium bichromate 0.2 g. oxalic acid 0.5 g. dextrin 0.75 g. water: 80, 120, 160, 200, 240 or 280 cc. Fig. 3 shows the results, and too diluted solution is not fitted naturally because of low blue density. our experiments, satisfactory results were obtained using 80 or 120 cc of water.

Fig. 3 Influence of the concentrations of sclutions.

It was found out that the dependence of maximum blue density upon concentration of sensitive solutions becomes inconsidelable when the quantity of ferricyanide is increased. So, if we add more ferricyanide, the influence of concentration will decrease. Nominate the above composition as I, and then make the compositions II and III adding 2 g. or 4 g. of ferricyanide to I respectively. Using I, II and III, the following maximum blue densities were observed for each test piece.

[III] Influence of ferricyanide. Blue print compositions containing ferric ammonium oxalate and sodium ferricyanide are always tested in our studies, and in this case, ferricyanide is a colour-forming component though it has slight sensitivity to light. It is shown clearly in the preceeding section, that higher maximum blue dentities can be observed in blue print having higher ferricyanide content. But, as to light sensitivity, it decreases with raising ferricyanide content. We prepared the following sensitive solutions : 10 Y. TOMODA Bull. Soc. Sci. Phot. Japan

ferric ammonium oxalate 12 g.

sodium ferricyanide 0.5, 1.0, 2.0, 4.0, 6.0 or 8.0 g. water 80 cc.

Sensitometric results are shown in Fig. 4, where oxidizing bath containing 2 % sodium ferricyanide is used specially for a test piece corresponding to leftend curve in Fig. 4.

From these results, energy values necessary to obtain blue density of 0.5, 0.7 or 0.9 are determined on the H & D curves and the relation between reciprocal of the energy value 1/E•~108 and quantity of ferricyanide is plotted as shown in Fig. 5.

Fig. 4 Influence of the quantities of Fig. 5 Dependence of sensitivities on sodium ferricyanide. the quantities of ferricyanide.

Thus, in our experiments, log(1/E+c) was proportional to log(g. of ferricyanide) where c are constants 2.6, 3.1 and 3.5 for D=0.5, 0.7 and 0.9 respectively, so sensitivity falls rapidly with increase of ferricyanide content. This result can be explained by the fact that ferricyanide is an oxidizing agent which restrains photo-reduction of ferric ammonium oxalate. [IV] Addition. agents. Photographic properties of blue print may be improved by addition agents such as salts of organic acids, inorganic salts or amines, but the effect of addition of these agents is not known exactly. First cf all, sodium oxalate, ammonium oxalate, sodium acetate, sodium formate, citrate and potassium-sodium tartrate were added to sensitive solutions of the following composition. Ferric ammonium oxalate 12 g. Sodium ferricyanide 2 g. Ammonium bichromate 0.2 g. Water 80 cc. Salt of organic acid 0, 1, 2 or 3g. Maximum blue densities and r values of the test pieces were as follows:

According to the results, addition of sodium oxalate and acetate was effective and sensitivity and maximum density of blue print increased but beyond the proper quantity No. 4-5, Dec., 1955 BLUE PRINT MATERIALS 11

of addition, desensitization accompanied with marked increase of contrast will be obser- ved. Sodium citrate and tartrate were ineffective, but sodium formate showed sensitizing effect specially in combination with formic acid. Aqueous ammonia, pyridine and triethanolamine were examined as addition -agents and slight desensitizing action was always observed. Addition of triethanolamine makes blue print to have very high contrast. Thiourea, guanidine carbonate and sodium nitrite were also tested and the sensitizing effect of guanidine salt was confirmed, but addition of thiourea resulted in making fog. Sodium nitrite had also a remarkable effect for increasing contrast of blue print.

[Y] Oxidation reduction potentials. Photographic sensitivity of blue print is based on photoreduction of ferric salt, and reaction speed of ferric salt can be observed in solutions by measurements of their redox potentials. Immersing a platinum electrode into test solution in a quartz beaker, potential difference was measured between platinum and 1-N calomel electrode. Potential value varies gradually even when we put the beaker in a dark room, but remarkable decrease of potential due to photoreduction of ferric ions in solution can be observed if we throw an ultraviolet light on the solution.

Fig. 6 Redox potentials of ferric ammonium oxalate solutions. Figure 6 shows these variations of potentials in Eh(volt) of a solution containing 4.460 g. of ferric ammonium oxalate in water or in buffer solutions composed of sodium hydroxide and potassium dihydrophosphate. It is clear that the potentials of solutions decrease rapidly under illumination and this represents reduction of ferric ions to ferrous

Fig. 7 Redox potentials of solutions of Fig. 8 Redox potentials of ferric ammonium various concentrations. citrate in buffer solutions. 12 Y. TOMODA Bull. Soc. Sci. Phot. Japan

state. Fig. 7 shows potential curves of sulutions of various concentrations of ferric ammonium oxalate. Measurements were carried out also dissolving 2.029 g. of ferric ammonium citrate in 1 liter of water, but the potential decrease occurred more slowly in comparison with oxalate, and this suggests lower light sensitivity of ferric ammonium citrate (Fig . 8) . In the case of ferric ammonium oxalate, potential fall in darkness was observed as shown in Fig. 7, but potential of ferric ammonium citrate solution varied to higher value. Moreover, ferric ammonium citrate showed more rapid fall of potential in dihydropho- sphate buffer solution than those measured in potassium phthalate buffer solutions even in the same pH. Potential curves of ferric ammonium oxalate solutions containing organic acids are shown in Fig. 9, where potentials are generally high; that is, the solutions are somewhat resistant to reduction by light. Here, the exceptional behaviour of formic acid is noticed and the low potential value at initial point might be due to reducing action of formic acid and such reagent can be used as sensitizer for blue print.

Fig. 9 Influence of addition of organic acids . Fig. 10

When salts of organic acids such as sodium oxalate , acetate, formate or citrate were added to the ferric ammonium cxalate solution , potential curves were found in a lower position as shown in Fig. 10 and the effect of addition of sodium oxalate was most remarkable. As in the case of formic acid , sodium formate also lowered the initial potential of the solution. Thus, potential measurement of sensitive solutions presents a basis for estimation of sensitivity of blue print compositions , though we cannot discuss exactly in detail, but according to our results, it is possible to say that an addition agent which lowers potential value of ferric ammonium oxalate solution, can be used as sensitizer for blue print, just as in the case of our experiments with sodium oxalate, formic acid, sodium formate or guanidine carbonate. There may exist some exception such as potassium dihydrophosphate which lowers redox potential but has desensitizing effect .

Summary

1) Photographic properties of blue print were discussed using H & D curves which were obtained following the example of silver halide emulsions. Formation of Turnbull's Blue and its bleaching was observed and the existence of reciprocity law failure was demonstrated. 2) Compositions of blue print sensitive solutions were discussed and optimal con- centration was shown. Then, the role of sodium ferricyanide was discussed and the influence of its content upon sensitivity of blue print was clarified . No. 4-5, Dec., 1955 POLAROGRAPHS OF DEVELOPING AGENTS 13

3) Addition agents were discussed and suitableness of sodium oxalate, formate was pointed out. 4) Redox potentials of sensitive solutions of ferric ammonium oxalate and ferric ammonium citrate were measured and the effect of addition of some organic acids or their salts were discussed.

LITERATURE

1. A. HNATEK: Phot. Korr., 87, 37, 40, 44. (1951) 2. S. SUZUKI: RPS Centenary Conference 1953. 3. Hay, S Handb. d. wiss. u. ang, Phot., Vol. 5, p. 459 etc, 4. E. STENGER: Z. wiss. Phot., 30, 45, (1932) 5. H. D. MURRAY: J. Soc. Chem. Ind., 59, 645. (1940)

Bulletin of the Society of Scientific Photography of Japan, No. 4-5, Dec., 1955

THE POLAROGRAPHIC STUDIES OF DEVELOPING AGENTS WITH THE ROTATING PLATINUM ELECTRODE (Received Sept. 14, 1955) Shinichi KIKUCHI& Kenichi HONDA Institute of Industrial Science, University of Tokyo

Introduction

The polarographic method is the best one among analyses of organic substances. Therefore authors have usually wished to use this method for the rapid determination of developing agents. But as developing agents are oxydized at the anode, the usual mercury drop electrode is not preferable, because this does not give the fair result, being covered by the oxide film at the anode. The platinum rotating electrode was tried for this purpose. Meanwhile the laborious work of Bent and others1) on the polarograpic studies of dialkylanilines with the rotating electrode was reported. Recently Russian authors, S. G. Bogdanov and N. S. Sukhobekova2) have done the amperometric titration of developing agents with the rotating platinum electrode. Reports concerning the rotating platinum electrode are very scarce compared to the mercury drop electrode. In the first part of this report, the authors wish to describe the basic conditions for the rotating platinum electrode to obtain the good diffusion current.

The method of experiment. Basic conditions

The varying potential is applied to the salution by the ordinary manner and the small diffusion current is amplified in order to drive the self recorder of the milliam- meter type. (Fig. 1) The circuit of this amplifier was already reported in an other paper.3) [I] The size and the manner of attachment of the platinum electrode. The size of the platinum electrode should be very small to obtain the polarization. Two types of the platinum electrode were tried in this experiment, one vertical, the