ch 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 1/2-plates or four dozen 31/4 by 31/4,
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 1/2 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
nitrate of silver, and 2 drops of hydrochloric acid per ounce. Put this
in your stock solution bottle, and keep it in a dark place for
twenty-four hours. When first put in, it will be milky; when taken out,
it will be creamy; and it will be well to shake it once or twice in the
twenty-four hours.

At the end of this time you can make your two dozen plates in about an
hour. Proceed as follows: Have two porcelain dishes large enough to hold
four or six of your plates; into one put sufficient clean water to nearly
fill it, into the other put 30 ounces of clear, flat, _not acid,_ bitter
beer, in which you have dissolved 30 grains of pyrogallic acid. Pour this
through a filter into the dish, and avoid bubbles. If allowed to stand an
hour, any beer will be flat enough; if the beer be at all brisk, it will
be difficult to avoid small bubbles on the plate. At all events, let your
preservative stand while you filter your emulsion. This must be done
through perfectly clean cotton-wool into a perfectly clean collodion
bottle; give the em