best answer to that is, that it is used by a well-known firm of plate makers to prepare excellent plates. The following is the process, devised by Mr. Wilson, which won a prize offered by Mr. Paget in 1880.
To make a pint of emulsion select a 20-ounce, narrow-mouthed stoppered bottle, with a well-fitting stopper and thin bottom Make it perfectly clean. Make a stock solution of
Hydrochloric acid (pure) ... ... ... 1 fl. drm.
Put into the 20-ounce bottle
20 minims of the above dilute acid.
3 fluid ounces distilled water.
210 grains ammonium bromide.
80 grains Nelson's No. 1 photo, gelatine.
Leave the gelatine to swell for, say, fifteen minutes or longer. In a clean glass vessel (beaker, measure, or flask) dissolve 330 grs. of nitrate of silver (re-crystallised) in 3 ozs. of distilled water. Pour out about 2 fluid drms. of this silver solution into another small vessel (say test tube), and dilute it to half strength with an equal quantity of distilled water. Take the 20-ounce bottle and the two lots of silver solution into the dark-room. Mr. Wilson prefers to use a large paraffin lamp, protected by one thickness of ruby and one of dark orange glass to two thicknesses of dark orange paper without any ruby. In the dark room have a gas-boiling stove, and on it a tin pot or saucepan deep enough to contain the bottle when the lid is on. It should have a tin, perforated, false bottom to prevent the bottle resting immediately on the true bottom ; or a piece of wire gauze will answer. Let the pot contain some 3 or 4 ins. in depth of boiling water. Turn out the gas of the stove, if alight, and plunge the bottle into the water two or three times, so as to avoid cracking it by too sudden heating; then leave it in for a few minutes until the gelatine is completely dissolved. Do not leave it in longer than necessary for complete solution. Take it out, shake up, remove the stopper, and set bottle down on the table near your lamp, so that you can see what you are doing. Pour in, all at once, the 4 drms. of dilute silver solution. Put in the stopper, and shake up thoroughly, but not too violently, for about half a minute. Now pour in the