Potassium hyposulphite

Potassium hyposulphite, K2S204.—The hyposulphite is obtained in the form of trihydrate by a method analogous to that employed for the sodium salt. A solution of potassium sulphite containing free sulphurous acid is treated with zinc-dust, and filtered after precipitation of the zinc by addition of slaked lime. On mixing the solution with alcohol, the trihydrate is deposited in very unstable yellow crystals. When boiled with acetone or methyl alcohol and dried in vacuum, they... 

Iodide of potassium was employed for a similar purpose but these do not give results as satisfactory as the hyposulphite of soda introduced by Sir J. Her-schell. Other improvements by the latter philosopher have also to be recorded, whloh, though not bo important as the one just referred to, contributu, nevertheless, to the perfection of the art. This Is particularly the case with hie researches on the solar spectrum, the results of which have been already given, and by which he has laid the foundation of the principles of actinism, and brought it to its present comprehensive state,... 

To Fix and Finish tie Picture.—When the plate has been well washed after the development, by pouring water over it from a jug, the yellow iodide of silver should ho dissolved out by means of either a saturated solution of hyposulphite of soda, or a solution of cyanide of potassium—strength about five grains to the ounce of water. This should be poured over the plate, and should be allowed to run backwards and forwards over it until the whole of the yellow iodide of silver in the plato has disappeared aftor which it should bo thoroughly well washed, by pouring water over it from a jug, and sot up to drain and dry or it may be dried before a fire. It is then ready to bo varnished,... 

The picture should be fixed with cyanide of potassium, and not with hyposulphite of soda, for two reasons —first, because tbe cyanide removes more pnrfectly any organic compound of silver which might injure tbe color of tho picture 5 and, secondly, because the hyposulphite of soda injures the color by blackening the silver. 

When cyanide of potassium Is used to fix the picture, that is, to remove the iodide of silver, it has hut little action on the image, while It decomposes the iodide of silver, and forms a soluble double cyanide or silver and potassium, together with iodide of potassium. When hyposulphite of soda is used, the iodide of silver is decomposed, and the products are a solublo double hyposulphite of silver and sods, together with iodide of sodium. 

This acid is obtained by the direct nitration of p-carbomethoxyphenyl-arsinic acid at 0° C. by mixed acid, then allowing the temperature to rise to 20° C. The yield is about 75 per cent., and the product crystallises from water in coarse yellow prisms. When reduced by ferrous hydroxide, the acid yields 8-hydroxy-l 4-ben2isoxa2ine-6-arsinic acid (p. 429). IMien the nitro-acid is reduced by sulphiu dioxide and potassium iodide in-hydrochloric acid solution, a 70 per cent, yield of the diokloroarsine is obtained in rosettes of plates, very resistant to aqueous hydrolysis attempts to reduce this by stannous chloride or sodium hyposulphite have been unsuccessful. Ferrous hydroxide gives a small yield of 8-hydroxy-l 4-benzz soxazine-6-aisenoxide. 

Water-soluble initiators used in emulsion polymerization are preferentially sodium, potassium or ammonium persulphate operating at 50-80°C. Redox systems use hydrogen peroxide or a persulphate as the oxidizing moiety and sodium metabisulphite, sodium hydrosulphate (also known as hyposulphite or dithionite), sodium thiosulphate and sodium formaldehyde sulphoxylate as the reductant. 

If an aJooholio liquid be heated for a few momenta with I SO diluted with 1 0 and distilled, the distillate, on treatment with hAO, and potassium permanganate, and afterward with sodium hyposulphite, yields aldehyde, which may be recognized by the production of a let color with a dilute solution of fuchsin. 

Iron percfiloride and potassium sulphocyanide give a blood-red, decolourized by mercuric chloride potassium sulphocyanide and sulphuric acid a fine old port colour, cleared by the same agent Litmus solution and an acid produce red, also permanganate of potash and sulphuric acid, cleared by hyposulphite of soda. Potassium ferrocyanide and the double sulphate of uranium and potassium give an old port-like colour-washing soda clears it. 

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