In 8 ounces of absolute alcohol dissolve 5 drachms of anhydrous bromide
of cadmium. The solution will be milky. Let it stand at least twenty-four
hours, or until perfectly clear; it will deposit a white powder. Decant
carefully into an 8-ounce bottle, and add to it a drachm of strong
hydrochloric acid. Label this "bromide solution;" and it is well to add
on the label the constituents, which will be found to be nearly:

Alcohol. 1 ounce.
Bromide of cadmium. 32 grains.
Hydrochloric acid. 8 drops.

This solution will keep for ever, and will be sufficient to last two or
three years, and with this at hand you will be able in two days to
prepare a batch of plates at any time. In doing so, you should proceed
thus: Make up your mind how many plates you mean to make, and take of the
above accordingly. For two dozen ½-plates or four dozen 3¼ by 3¼,
dissolve by heat over, but not too near, a spirit lamp, and by yellow
light, 40 grains of nitrate of silver in 1 ounce of alcohol 0.820. While
this is dissolving in a little Florence flask on a retort stand at a safe
distance from the lamp--which it will do in about 5 minutes--take of the
bromized solution ½ an ounce, of absolute ether 1 ounce, of gun-cotton
grains; put these in a clean bottle, shake once or twice, and the
gun-cotton, if good, will entirely dissolve. As soon as the silver is all
dissolved, and while quite hot, pour out the above bromized collodion
into a clean 4-ounce measure, having ready in it a clean slip of glass.
Pour into it the hot solution of silver in a continuous stream, stirring
rapidly all the while with a glass rod. The result will be a perfectly
smooth emulsion without lumps or deposit, containing, with sufficient
exactitude for all practical purposes, 8 grains of bromide, 16 grains of