American cinematographer (Jan-Dec 1924)

December, 1924 AMERICAN CINEMATOGRAPHER Nineteen lOcc. of each solution was used. A measured amount of one-hundredth normal silver nitrate was added to the solution containing only gelatine, and the same amount of water to the solutions to be analyzed. Ice. of 1% sodium sulphide was added to each and the comparison made. By a few trials the amount of silver nitrate required to give the same turbidity in each case was found. The results calculated in terms of silver bromide are given in Table I. These figures, while not extremely accurate, are sufficient to show that the developing solutions are capable of dissolving a measurable amount of silver from the emulsions during development. Table I. Solvent Power of Developing Solutions for Silver Halides Developers Composition* oj Solu Formula tion in grams per liter NazCOz NazSOs KBr Emulsion Equivalent oj Silver Bromide per liter grams MQ tank 12.5 MQ tank 12.5 MQ tank 12.5 MQ tank MQ 25 MQ 25 16X 12.5 25 25 100 grams 18.75 18.75 18.75 18.75 75 75 100 grams 0.75 Eastman Motion Picture Negative Film 0.17 0.75 Eastman Motion Picture Positive Film 0.19 0.75 Eastman Brilliant Velvet Bromide Paper 0.21 0.75 Azo E No. I Developing Paper 0.60 1.5 Eastman Motion Picture Negative Film 0.15 1.5 Eastman Motion Picture Positive Film 0.15 3.75 Eastman Motion Picture Negative Film 0.56 ♦Reducing agents were omitted from the solutions. The effect of soluble bromide in diminishing the solubility of silver bromide is shown by the smaller value obtained with MQ25, which contains much more sulphite than MQ Tank, but more potassium bromide. (b) Precipitation by Lead Acetate or Silver Nitrate. When a small amount of lead acetate was added to the fogging developer containing sulphide, it was precipitated out so completely that the developer again gave entirely satisfactory results. The precipitated lead sulphide settled out quite rapidly but even while in suspension it caused no trouble in development. With a developer which contained 0.01% sodium sulphide, it was found that when 0.05% of lead acetate was added and mixed thoroughly with the developer, all the sulphide was removed. Any excess of lead salt forms a white precipitate which is probably a basic lead carbonate with possibly some sulphate or sulphite. It can easily be determined when sufficient lead salt has been added by observing whether further additions produce a white precipitate instead of a dark one. The solution must be thoroughly mixed and the first dark precipitate removed by settling or by filtering a small sample before making this test. A large excess of lead salt is objectionable because it removes from the solution some of the necessary carbonate or sulphite. The precipitation takes place most favorably if a comparatively dilute solution of the lead salt, for example, about 10%, is stirred in slowly. In most cases, not more than 0.5 gram of lead acetate crystals per liter should be required. When silver nitrate was added in order to precipitate sulphide from a developer, the results were not very satisfactory. The reduction of the silver interferes with the rapid precipitation of silver sulphide, and the precipitate settles much more slowly than that of lead sulphide. Moreover, the developers to which silver nitrate had been added showed a tendency to produce a spotted dichroic fog which looked as though it had been picked up from 6. I. I. Crabtree, The Development of Motion Picture Film by the Reel and Tank System. Trans. Soc. M. P. Eng.. No. 16. 163, (1923). the surface of the solution. It appears, therefore, that the most satisfactory way of removing sulphide from a developer is to stir in thoroughly a small quantity of a solution of lead acetate which precipitates lead sulphide. 2. Attempts to Prevent the Growth of Yeast. A series of solutions containing 1% thiosulphate and yeast were tested with various preservatives to see if the growth could be prevented. The substances added were phenol, 0.1% and 5%; thymol, sodium salicylate, 0.5% and 5% ; formalin, 0.1% and 0.5%. Sulphide was formed in all these tests except with formalin. When MQ tank developer was diluted 1 to 3 and 0.25% thiosulphate added together with yeast, sulphide was always formed. With this solution it was found that the addition of sodium salicylate in a concentration of 0.1% and 0.5% accelerated the formation of sulphide, while formalin in concentrations of 0.1% and 0.2% only acted as a retarding agent. Probably the sulphite in the developer combines with the formalin rendering it ineffective. In these tests, therefore, no substance was found which would prevent the growth of yeast in a developer. If the formation of sulphide is caused by some other type of organism perhaps it could be prevented more easily. At this time, however, the authors are unable to recommend any substance which can be added to a developer to prevent such growth. In case a tank of developer becomes affected, it should be thoroughly cleaned before a new batch is added in order to prevent infection from the tank. While the difficulties described in this paper arose with motion picture developers, these solutions are essentially the same as developers used in any other branch of photography. In motion picture work developers are used in large quantities and are frequently kept in tanks for several weeks. Such conditions are especially favorable to bacterial growth. However, the same phenomena may occur in any case where developers in either large or small quantities are kept after being used. Although the authors have not observed the bacterial formation of sulphide in unused developers, such an occurrence is not impossible. SUMMARY 1. Several samples of tank developer which suddenly began to give excessive fog were found to contain sodium sulphide. 2. The concentration of sodium sulphide in two of the fogging developers was determined photographically and found to be approximately 0.005% and 0.02% respectively. 3. When free sulphur was added to a developer, sodium thiosulphate or other poly-thio salts were formed but no sulphide could be detected. The formation of sulphide from thiosulphate or rubber in a developer is, therefore, improbable. 4. Many different organisms are capable of reducing hypo, sodium sulphite, and sodium sulphate to sodium sulphide. Certain unidentified fungi and several species of bacteria, some of them chromogenic, were found living in the fogging developer. 5. The formation of sulphide in developers was reproduced experimentally in the laboratory by adding yeast or slime. The evidence, therefore, indicates that the sulphide in the fogging developers investigated was formed by reduction of the sulphite by living organisms. 6. When a developer is used continuously, the dis (Continued on page 23)