I began at first with a thirtieth of the whole
quantity of gelatine, and increased that quantity to a tenth without the
precipitate forming with greater difficulty. The salts were dissolved in
the usual quantity of water, the bromide of potassium was added to the
separately-dissolved gelatine, and both solutions cooled in iced water.
I soon found that even this was not necessary. I accelerated the
solution of the salts by vigorous agitation, so that the temperature
became so much lowered that, even after the addition of the warm
gelatine, it still remained low enough to give the precipitate when
mixed. The mixing took place gradually, all the usual precautionary
measures being observed; such as pouring the silver solution into No.
2 in small quantities at a time, and constantly stirring, and the
separation from the mother lye was complete.
The formula according to which I worked latterly was as follows:
SOLUTION I.
Nitrate of silver...................... 463 grains.
Water................................... 163/4 ounces.
SOLUTION II.
Bromide of potassium................... 355 grains.
Iodide of potassium....................
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