THE BRITISH JOURNAL OF PHOTOGRAPHY. Volume 40, No. 1736, Aug 11, 1863, p.511

ON THE AMOUNTS OF SILVER AND HYPO LEFT IN ALBUMENISED PAPER AT DIFFERENT STAGES OF WASHING.

[London and Provincial Photographic Association.]

ANY one studying the literature of photography must be struck with the diversity of opinion expressed by different workers on the important points of fixing and washing prints, some recommending neutral and others alkaline hypo, and the strength of the fixing solution varying from five to thirty per cent., the length of time the print should be washed varying from one to twenty-four hours.

The danger of an acid fixing bath and its tendency to yellow the whites of a print, and in addition its doubtful fixing power, was first pointed out by Mr. J. Spiller in a paper he read before the Photographic Society of Great Britain on January 14, 1868. Mr. Spiller in his paper says that "a hint was thrown out by Messrs. Davanne & Girard to the effect that the so-called 'pure whites' of the albumen prints still retained a small proportion of silver in an insoluble condition, and most probably in the form of sulphide."

Further on, the author says: "My experiments went to prove that the metal was retained in the whites of the albumen print, and indeed in all parts of the coating, in the form of an argentic organic compound, colourless, unalterable by light, and comparatively insoluble in hypo sulphites and other fixing agents. It could not be a simple sulphide, for the test by which I discovered its existence in the paper was the production of a brown stain upon moistening the white surface with sulphide of ammonium." In a paper in the Photographic News for October, 1862, Mr. Spiller recommended the, addition of carbonate of ammonia to the ordinary hyposulphite fixing solution, for the double purpose of preventing by its alkalinity any chemical change or decomposition of the double hyposulphite ; and, secondly, of directly aiding by its special solvent properties in the removal of this organic compound of silver.

In carrying out this research, we had two objects in view: firstly,. to determine the time the print should be washed; and, secondly, to endeavour to determine the cause of the fading of the finished print.

Three sheets of albumenised paper from the 'same quire were sensitised on a fifty-grain neutral solution of nitrate of silver and allowed to dry in the dark. These were then cut into pieces 5½ in. x 8½ in. The pieces from one sheet were marked A, from the next B, and from the third C.

The paper thus cut up and marked was washed for ten minutes in running water till all free silver had been removed.

Two of these pieces, taken. from different sheets, which could be easily recognised from the, letters on the back, were placed on one side, in order to determine the amount of sulphur originally present in the paper and also the amount of silver that had to be removed by the fixing agent.

The remainder of the paper was placed in a pint and a half of a twenty per cent. hypo bath; and, as this gave a little, more than, two ounces of hypo per sheet of paper, we consider we were on the safe side, as Captain Abney says that one ounce of hypo will fix three sheets of paper.

The hypo bath was tested before and after use, and was found to be slightly alkaline to litmus. The temperature was 22.4° C.

The prints were kept in the bath with constant changing for fifteen minutes. Two pieces (again from different sheets) were then taken and allowed to drain for five minutes, and the total sulphur and the remaining silver to be removed by washing determined.

The remaining pieces were then placed in a large vessel filled with water and into which water was constantly flowing. The temperature of the water was 13° C. During the first hour the pieces of paper in the water were constantly turned over in order to prevent them sticking.

Two pieces were removed at the end of 5, 10, 15, 25, 40, 60, 90, and 120 minutes, and 19 hours, and the amounts of silver and sulphur remaining in them determined.

The estimation of the sulphur and silver in the papers was carried out as follows :--In each case the two pieces of paper were allowed to drain for five minutes, and 'then torn up into small pieces and placed in a large beaker, with a mixture of 100 c.c. of nitric acid and 200 c.c. of strong hydrochloric acid (free from sulphur), covered with a dark glass, and heated on a sand bath till the paper was completely destroyed. The solution was then taken down to dryness, and 250 c.c. of pure distilled water and three drops of hydrochloric acid added, and the whole heated to boiling, allowed to cool and filtered, and the filter paper and beaker washed with boiling water. The filtrate was heated to boiling, and chloride of barium added, which precipitated all the sulphate present as barium sulphate. This was then collected on a filter, dried, and weighed in the usual way, and from this the amount of sulphur present in the paper calculated.

The chloride of silver on the filter was then dissolved out with ammonia, and precipitated by means of nitric acid, filtered off and treated in the usual manner.

The figures obtained are as follows

The amount of sulphur in original paper has been subtracted from results 4 to 12 inclusive

From these figures it will be seen that after five minutes' washing 97.2 per cent. of the sulphur originally present has been removed, after ten minutes 98 per cent., and that, however long-continued the washing, no more of the sulphur can be eliminated. Turning to the silver, we find that as the paper comes from the fixing bath it has lost 88.3 per cent. of its silver; after washing for. five minutes, 93.1 per cent; and, after 10 minutes, 95.3 per cent. After ten minutes washing the amounts of silver and sulphur remain constant.

It is evident from these figures that the permanency of a print does not depend so much on the washing it receives as on its thorough fixing; and we are strongly of opinion that the best way of removing all the silver is not by using two baths if hypo in succession, but by washing for about five minutes after the first bath, and then soaking in a second fresh bath of hypo.

In what form the silver occurs in the paper, whether as soluble AgNa₄S₂O₃, or the soluble Ag₂Na₄3S₂O₃ held in a "loose combination" with the films of the paper, we are unable to state. However, the fact remains that, after a more thorough and fixing than prints generally get, .246 of a grain of silver in each 22 x 17 in. sheet of paper: and this, which is probably in the form of hyposulphite in the presence of light and organic matter is reduced to silver sulphide, and will easily account for the yellowing of the whites of prints after a time.

We had hoped to determine the silver and sulphur in gelatino-chloride paper, and the silver in paper that has been treated to several baths of different composition; but, owing to the length of time required to carry out these experiments, we have been obliged to defer the investigation of those points for a for a future occasion.