Ammonium Citrate 2 26.—An extremely deliquescent salt, and not easy to keep in any form. It is expedient to prepare as required by neutralising 12 parts of citric acid with II parts strong ammonia, added gradually, and then making up to 24 parts with distilled water. Used as a restrainer in developing over-exposed plates, and in some emulsion formula:.
Ammonium Iodide, NH,,I, 145.—Solubility i in of cold water, 1 in 4 alcohol, and very soluble in ether or mixtures of alcohol and ether.
Ammonium Persulphate 228.—Large colour less crystals. Strongly acid. Solubility i in 11 cold water. Used chiefly in solutions of about 2 per cent. as a reducer of the high lights in negative. A solvent of gelatine.
Sulpho-Cyanide, 76.—Colourless deliquescent crystals. Best preserved in solution. Solubility in o•6 cold water. Used for toning gelatino-chloride papers, and is also a fixing agent, but its high price prevents any competition with the ordinary " hypo." Amyl Acetate, 13o.—An amyl ester boiling at 140', and having the odour of jargonelle. Is used in dis solving pyroxyline when preparing celluloid.
Anthion.—A name under which potassium persulphate is marketed for the elimination of hypo from plates and films.
Aqua Fortis.—Nitric acid.
Aqua Regia.—A mixture of nitric acid i part, hydrochloric acid 3 parts, used for dissolving gold and platinum.
Barium Chloride, 244.—Tabular transparent crystals. A solvent of gelatine, used for making baryta paper and fine-grained focussing screens for photo-micrography. Sometimes also added to salting solutions for albumenised paper.
Benzole, 78.—Also known as benzine. A colourless, volatile liquid, with a smell much resembling coal-gas, obtained by distillation of coal-tar. Gives off an explosive vapour, and boils at about 178' Fahr. Used for removing grease and oil, for making certain varnishes, and also as a vehicle for bitumen in engraving processes.
Borax, see Sodium Borate.
Calcium Carbonate, too.—Occurs in nature as common chalk, but for photographic purposes is precipitated artificially. It is used principally for neutralising chloride of gold solutions.
Calcium Chloride, t t L—Chiefly used in the anhydrous state in the calcium tube for preserving platino type and similar papers from the effects of damp. It is
a very powerful absorbent of water, and when moist has only to be heated in an oven to render it ready for use again.
Citric Acid, 2!o.—Colourless, odourless crystals with strong acid taste. Prepared from the juice of fruits, such as lemon and lime. Solubility t in / of cold water. Used as an acidifier in various sensitised papers and clearing solutions.
Copper Bromide, 223.3.—Gray-blue powder or light blue needle crystals. Deliquescent, and very soluble. As used in intensifying solutions is prepared generally from the sulphate salt by mixing solutions of copper sulphate and potassium bromide, filtering off the precipitated potassium sulphate.
Copper Sulphate, 249•5.—Blue copperas, or blue vitriol. Large bright blue crystals. Sometimes used as an accelerator to the ferrous-oxalate developer, in which it retards oxidisation of ferrous sulphate.
Eau de Jayelle.—A hypochlorite of sodium or potash, made by stirring up an ounce of chloride of lime with about 2 oz. of potassium or sodium carbonate in io oz. of water, and filtering.
Ether, 74.—Commonly called sulphuric ether. A colourless, very volatile liquid, of characteristic smell. Evaporates quickly, and when applied to the skin leaves sensation of extreme coldness. Boils at 95 ' Fahr. A solvent of rubber, and collodion, in the preparation of which lies its chief value to the photographer.
Ferric and Ferrous Salts, see Iron.
Formaline.—A 40 per cent. solution in water of formic aldehyde, A colourless, somewhat volatile liquid, with a very pungent, irritant odour. Used for hardening gelatine films in hot weather, a 5 per cent. solution rendering plates and films practically safe from injury, even in boiling water. It also adds brilliancy when employed in place of alkali in pyro and some other developers.
Glycerine, 92.—A colourless, odourless syrup of sweet taste, obtained from animal and vegetable fats during the process of saponification as a bye-product. Soluble in water and alcohol. Chiefly employed in photography to render gelatine films more pliable, and to prevent them from splitting.