The Dictionary Of Photography

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Potassium Chloroplatinite                    Potassium Cyanide
75 of water; insoluble in alcohol and ether. It is extremely deliquescent - that is, absorbing moisture from the air - and becomes a pasty mass. It is used for developing, and for the preparation of the other salts of potash. It should not be con-founded with the bicarbonate or acid carbonate of potash (KHCO3), which is a much less active salt.
Potassium Chloroplatinite (Ger., Kaliumplatinchloriir, Pla-tinkaliumchlorur; Fr., Chloroplatinite de potassium; Ital., Cloroplatinito di potassid). K2PtCl4 = 3186. This is prepared by heating 50 parts of bichloride of platinum dissolved in 100 parts of water to jooo C, and passing through it a stream of washed sulphurous anhydride, S02, till the solution turns deep red, and gives no precipitate with ammonium chloride. The solution is then allowed to cool, and 25 parts of potassium chloride in 50 parts of water added, and the solution allowed to crystallise, and the crystals washed. It occurs in ruby red deliquescent crystals, very soluble in water, insoluble in alcohol. It is used in platinotype printing and for toning prints. A convenient method of preparing this salt for the platinotype process is that given by Hoffman : - Take of platinum in scraps 5 parts, dissolve in aqua regia, and evaporate carefully till the solution is syrupy ; add 5 parts of potassium chloride dis-solved in a little distilled water; then evaporate down till it forms a mass. Dissolve the mass in sufficient water to make 100 parts. To the 100 parts of this solution add 10 parts of dry ferrous oxalate, and heat in a capsule for about two minutes at 1580 F., and allow to cool and filter. Double decomposition takes place, and a mixture of ferric oxalate and chloroplatinite is formed.
Potassium Cyanide (Ger., Cyankalium, Kaliumcyanid; Fr., Cyanure de potassium ; Ital., Cia?iuro dipotassio. KCN or KCy = 65. Synonyms: Cyanide of Potash, "Cyanide." Obtained by fusing ferrocyanide of potassium with carbonate of potash. The resulting fluid mass is poured out on slabs, and then broken up into the irregular masses met with in commerce. Solubility, 1 in 1 of cold, 122 per cent, in hot water; 1-2 per cent, in abso-lute alcohol; more soluble in dilute alcohol. It is used for reducing the density of negatives, and for fixing in the wet process. It is extremely poisonous when taken internally, and