AMMONIA (Pr., Ammoniaque ; Ger., Ammo niak, Ammoniakwasser, Salmiakgeist) A volatile, pungent gas, which for photographic and many other purposes is used in the form of a watery solution ; formerly known as " spirit of hartshorn." The strongest solu tion, and that mostly used, is of •88o sp. g., contains 35 per cent. of the gas and is commonly known as " ammonia •88o " or " liq. ammon. fort." " Liquid ammonia " is the incorrect, popular form of the term " liquor ammonia?." A weaker liquor, kept by most chemists, one-third the strength of the -88o solution, is rarely used in photography. Ammo nia has many uses in photography, the principal being as an accelerator in the pyro developer, for blackening the mercury-bleached image in intensification, in emulsion-making, and as an addition to the bichromate bath for sensitising carbon tissue. Liquor ammonim should be kept in a glass-stoppered bottle, as it loses its strength rapidly if exposed to the air, and cork stoppers very soon deteriorate. The fumes of ammonia are extremely irritating to the eyes, throat, and nose, and particular care should be taken when opening bottles of it in hot weather, or when the bottles have been left on a warm shelf, as the liquid may spurt out and cause serious damage. Bottles containing liquor ammoni should be kept in a cool place, as heat develops great pressure, which may blow out the stopper or burst the bottle.
A. Haddon states that experiments show that ammonia expands on dilution with water about x8 per cent., and points out how very un reliable and varying is a solution of ammonia in hot weather, freshly bought samples of the •88o solution varying in specific gravity from that to -904, or from 35.8 to 26.9 per cent. volume. It is this variation that makes it unreliable as an accelerator in development ; hence the necessity of using it fresh or keeping it in a gas-tight bottle and in the cool.
In process work, ammonia is not largely used. It is added to the albumen bichromate solution and also to the fish-glue solution to neutralise acidity, and increase the keeping qualities. A few drops added to the developing water makes the albumen bichromate image develop more quickly. A dilute solution of ammonia with whiting is used for cleaning copper, to free the surface from grease. Perchloride of iron solution for etching, especially for photogravure, is often neutralised by the addition of ammonia. Added to copper sulphate until a bright blue solution is formed, ammonia makes a bath for coating zinc with a film of copper without the use of an elec tric battery.