Borax, see Sodium Borate.

Calcium Carbonate, CaCO3, 100

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, CaCl2, III

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, C6H8O7H2O, 210

Colourless, odourless crystals with strong acid taste. Prepared from the juice of fruits, such as lemon and lime. Solubility 1 in 3/4 of cold water. Used as an acidifier in various sensitised papers and clearing solutions.

Copper Bromide, CuBr2, 223.5

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, CuSO45H2O, 2495

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 Javelle

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 10 oz. of water, and filtering.

Ether, C4H10O, 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 950 Fahr. A solvent of rubber, and collodion, in the preparation of which lies its chief value to the photographer.

Ferric And Ferrous Salts

Ferric And Ferrous Salts, see Iron.


A 40 per cent. solution in water of formic aldehyde, CH20. 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, C3H5(OH)3, 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.

Gold Chloride, AuCl3, 3O3

The commercial forms usually obtained are either (1) bright yellow crystals, consisting of the chloride in combination with one equivalent of hydrochloric acid, made by dissolving gold in aqua regia and evaporation; (2) potassio-chloride, yellow hexagonal needles; (3) sodio-chloride, yellowish-brown deliquescent needles, the latter being the variety most commonly sold. The anhydrous chloride is of a yellowish brown colour. The comparative values are shown by the table below:


Gold Chloride.

Cryst. Gold Chloride.

Gold Potassio-Chloride.

Gold Sodio-Chloride.


























Gold chloride solutions are sensitive to light, and must therefore be kept in the dark.

Hydrochloric Acid, HCl, 36.5

The commercial impure forms, known as muriatic acid or spirits of salt, are unsuitable for most photographic purposes. Colourless, fuming liquid, with strong smell of chlorine. A dangerous corrosive poison. Antidotes'. Milk, gruel, etc., with magnesia, chalk, or other carbonates.

Hydrogen Peroxide, H2O2, 34

A colourless solution of sharp taste. Powerful oxidiser and bleacher. Used in extremely weak solutions as a hypo eliminator (1 in 1000 parts of water).

Hydrofluoric Acid, HF, 34

A colourless gas, generally supplied in hydrated form, obtained by heating fluorspar with sulphuric acid in a leaden or platinum retort. Even when dilute, it causes very painful ulcers on skin and nails. Must be stored in rubber bottles, as it dissolves glass, hence its use in detaching the gelatine film from glass plates.

Iron Ammonio-Citrate (Brown), 4 FeC6H5073(NH4)3C6H507 3Fe(OH)3, 2030. (Green), 5FeC6H6072(NH4)3C6H507NH4 C6H7072H2O, 1956

Small, shiny, reddish-brown scales of hygroscopic character. Prepared by dissolving ferric hydrate in citric acid, and adding ammonia till neutral. Solubility, 1 in 0.5 parts water. Chiefly used for the blue prussiate printing-paper.

Iron Ammonio-Oxalate (Ferric), (NH4)3Fe(C2O4)H2O

Greenish-white crystals, decomposed by light. Prepared by dissolving ferric hydrate in acid oxalate of ammonium solution. Employed in some platinotype processes.

Iron Oxalate (Ferric), Fe2(C2O4)3, 376

Obtained by precipitation, or by mixing ferric hydrate in the syrupy state with finely crystallised oxalic acid, and keeping for a few days in a dark, cool place. Not very soluble in water, but soluble in oxalic acid or alkaline oxalates. The sensitising agent in most platinotype processes.

Iron Oxalate (Ferrous), FeC2042H20, 180

A light-yellow crystalline powder. Almost insoluble in water. Rarely used dry, and is usually created as a developing agent by the admixture of neutral potassium oxalate and acid ferrous sulphate.

Iron Perchloride (Ferric), Fe2Cl6, 325

Yellowish-red opaque masses; very deliquescent. Solubility, 160 per cent. in cold water; also soluble in alcohol and ether. Used as a reducing agent in copper etching, and also occasionally as a sensitiser. From its property of hardening gelatine, which becomes again soluble when, on exposure to light, the salt is converted into a ferrous chloride, perchloride of iron was formerly recommended for the making of negative transparencies by the carbon process.

Iron Sulphate (Ferrous), FeSO47H2O, 278

Green vitriol or copperas. Green crystals, which absorb oxygen from the air, when they become covered with a brownish rust. This must be rejected. Solubility, 1 in 1.5 of water. Used for the developer in the wet-plate process, and also as a constituent of the ferrous-oxalate developer.

Lead Acetate, Pb(H3C2O2)23H2O), 379

White prismatic crystals of sweet taste; poisonous.

Lead Nitrate, Pb(NO3)2, 331

White opaque octahedral crystals; poisonous.

Both of the above are sometimes added to combined toning baths, but are of doubtful value. They are also added to the fixing-bath (1/2 oz. to the pint) for the purpose of direct toning by the deposition of sulphide of lead on the image. A few drops of nitric or acetic acid are required with these salts, to dissolve the certain amount of basic salt present in the solid crystals.