Commercial Aqueous Ammonia differs in many ways, and contains certain impurities. The sp. gr. diminishes of course with the amount of ammonia present, but should be about .940. A table is given, however, at the conclusion of this article to enable one to determine the quantity of ammonia present by the specific gravity of the liquid. Solution of ammonia absorbs carbolic acid rapidly from the air, forming carbonate of ammonium. It is therefore necessary to keep in a well-stoppered bottle, and to avoid leaving the mouth open as much as possible. A good plan is to smear the stopper with vaseline, which makes it fit perfectly close, and prevents it from becoming fast.
Aqueous ammonia may contain the following impurities : Chlorine, which may be detected by adding a small quantity of nitrate of silver ; it gives a cloudiness. Lime, which gives a pre cipitate with oxalic acid left as a solid residue on evaporation. Empreumatic oil ; it then has a yellow color and a disagreeable smell.
Pure aqueous ammonia is a colorless liquid, smelling of ammonia, and has a sharp burn ing, urinous taste. A perfectly saturated solution freezes between —100 and— 105 degs. Fahr., forming shining flexible needles. At —12o deg. Fahr. it solidifies to a gray gelatinous mass almost without smell.
Liquid ammonia possesses the property of dissolving many salts which are insoluble in water. Its principal uses in photography are in the emulsion process for dry plates, and in the developing and intensifying of the image. It is also used in the positive process, when sensitized
albumen paper is subjected to its fumes, and by this means increased sensitiveness and brilliancy are obtained. It dissolves silver chloride, and for this reason has been recommended as a fixing agent. It has only a slight solvent action on silver albuminate, however, and is therefore of no use wtih albumen paper. For plain salted paper it answers the purpose very well, and is said to be even superior to hypo. The bath recommended is made up of 44 ounces to liquid ammonia in zo of water.
In development, ammonia is used as the accelerator by rendering it alkaline and so en hancing its deoxidizing power, and it possesses the advantage over all other alkalies of giving greater brilliancy and vigor. With some makes of plates, however, ammonia will produce green fog. In published formula ammonia with specific gravity of .88o is generally recommended. It should, however, be tested by the accompanying table, as it is difficult to obtain with so low a specific gravity.
Ammonia can be detected by its changing red litmus paper blue or by its smell, and also by its formation of a white precipitate with solutions of mercuric chloride. Solutions of ammonia are more stable the more dilute they are ; therefore, it is advisable to add plenty of water and use proportionately.