The ferricyanide had a small influence and, as might be expected, hyposulphite is fatal to the assay. |
The picture may now be fixed by the use of the hyposulphite of soda, as in the preceding process. |
The hyposulphite, however, is the safest, both for the plate and for the operator. |
I develope the image by a very weak solution of sulphate of iron, and fix with hyposulphite of soda. |
The resulting clear, deep brown-coloured solution is treated with hyposulphite of soda solution until quite colourless. |
It is as hard to get rid of from the copper as hyposulphite is from a negative. |