Three sheets of albumenized paper from the same quire were sensitized on a fifty-grain neutral solution of nitrate of silver and allowed to dry in the dark. These were then cut into pieces 5i in. x 8f 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 recognized 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 deg. 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 deg. 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, to, 15, 25, 40, 6o, 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 too 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 25o c.c.
of pure distilled water and three drops of hydrochloric acid added, and the whole heated to boil ing, 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 sul phate 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: 1. Weight of sulphur in original paper .005o grammes 2. in water adhering to paper .000032 grammes 3.in paper fixed but not washed .2243 grammes ..
4-after 5 minutes' washing .0063 grammes 5- to 0045 grammes 6.15 .co48 grammes , 14 7. " 25 .0044 grammes 8. it 40 .0043 grammes 9. 14 b0 .0o46 gramme= ro. 41 90 .0047 grammes II. 120 .0045 grammes hours' ' .0047 grammes it The amount of sulphur in original paper has been subtracted from results 4 to 12 inclusive.
1. Weight of silver in paper unfixed .0734 grammes 2. . fixed but not washed .0086 grammes 3. 41 ' after 5 minutes' washing ... .0051 grammes 4. u... ... ..... .0035 grammes 5. .. ,. 15 .0037 grammes 6. ., .. 25 ., ... .0037 grammes 7- 40 oo33 grammes 8 .. .. 6o .. , .. . .0036 grammes 90 ... .0038 grammes " " . to. .. 120 ... . . . . .004o grammes 11.19 hours' .0039 grammes From these figures it will be seen that after five minutes' washing 97.2 per cent. of the sul phur 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 ten minutes, 95.3 per cent. After ten minutes' washing the amounts of silver and sulphur remain constant.