The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Potassium Metabisulphite                      Potassium Oxalate
It is used for iodising collodion, in emulsion making and as an ingredient of some intensifiers.
Potassium Metabisulphite (Ger., Kaliummetabisulfit; Fr., Metabisulfite de potassium, Bisulfite or Sulfite acide de potasse ; Ital., Metabisolfito di potassd). K2S205 = 222. Prepared by saturating solution of potassium carbonate with sulphurous acid gas and precipitating the metabisulphite with alcohol. Solubility : 1 : 3 of water, insoluble in alcohol. It is used as a preservative of pyrogallol, but on keeping becomes very acid and necessitates therefore the use of larger quantities of alkali. It may also be used as an addition to the fixing bath to make the same acid and prevent it staining.
Potassium Nitrate (Ger., Salpetersaures Kali, Kaliumnitrat, Salpeter, Kalisalpeter; Fr., Azotate de potasse, Nitrate de potasse, Salpetre selde nitre; Ital., Azotato di potassd). KNO3 = 101. Synonyms: Nitre, Saltpetre. Occurs naturally in many parts of India, contaminated with nitrate of calcium. It is also made artificially by the process of nitrification. It can also be made by adding chloride of potash to nitrate of sodium in solution. Solu-bility : 30 per cent, in cold, 335 per cent, in hot water; insoluble in cold alcohol, 2 per cent, in boiling alcohol. It is used for making nitric acid, pyroxyline and for magnesium flashlight powders.
Potassium Nitrite (Ger., SalpetrigsauresKali, Kaliumnitrit; Fr., Azotite depotassimn; Ital., Azotito dipotassio). KNOz=85. Can be made by heating nitrate of potassium, when oxygen is given off and the nitrite left. It is an extremely deliquescent salt, and of but little use photographically, it being recommended for preparing the paper for Actinometers (q.v.), and for preventing commercial sensitised paper from yellowing.
Potassium Oxalate (Ger., Oxalsaures Kali, Kaliumoxalat; Fr., Oxalate neutre de potassium; Ital., Ossalato neut?'o di potassd). K2C204 = 164. Synonym : Neutral Oxalate of Potash. Pre-pared by neutralising oxalic acid with carbonate of potash or caustic potash. Solubility: 1 in 3 of water; insoluble in alcohol or ether. . It is used for the production of ferrous oxalate, and as a developer in the platinotype process. A convenient method of making it is as follows: - Dissolve 13 ozs. of carbonate of potash
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