38 IX-Note on some Double Thiosulphates. By J. B. COHEN . Ph.D. Assistant Lecturer Owens College, Manchester. Hydrated Potassium Czcprous Thiosulphate. RAMMELSBERG found that when cupric sulphate or acetate is added to a solution of potassium thiosulphate and the resulting green liquid is allowed to stand sulphur-yellow crystals are deposited consisting of a double thiosulphate of copper and potassium of the formula R2S~OJ,Cu2S20,,2H,O. These crystals are needles grouped in clusters, and are readily decomposed on warming with water copper sulphide being deposited. If however the addition of potassium thiosulphate be continued until the green colour disappears and gives place to a pale yellow tint (1 part of hydrated cupric sulphate requires about 2 parts of potassium thiosulphate) the resulting solution may be boiled for a long time and only a very slight deposition of a brown precipitate occurs.On standing this solution deposits a small quan-tity of brilliant orange-coloured crystals which consist of groups of six-sided prisms terminated by basal planes and belong to the hexagonal system. The crystals were washed with cold water dried in the air and analysed with the following results :-Found. Calculated for r----h-- 1 H,O 8-03 7.53 -K 23.21 - 23.27 23.34 - -Cu 18.74 - 19.62 - 19.51 19.67 S - - 27.57 - - 28.57 CU.LS,O~,~K,S,O,,~H,~. 1.X 11. 111. IV. V. - - -The substance cannot be recrystallised from water as it is scarcely soluble in the cold and dissolves with slight decomposition in hot water. Hydrochloric acid decomposes it with evolution of sulphur dioxide and the formation of copper sulphide.Caustic soda preci-pitstea cuprous oxide and if exposed to the air in contact with ammonia it dissolves forming a blue solution. It may be distin-guished from Rammelsberg's salt by its crystalline form its greater stability in hot aqueous solution and by the fact that the slight decomposition which then occurs is not accompanied by the formation of sulphate. It may be kept unaltered iu the air for several days, but slowly blackens after several weeks even in a well-closed vessel. It immedia.tely turns black when heated to 100-110". * Each number denotes a fresh preparation of the salt COHEN ON SOME DOUBLE THIOSULPHATES. 39 Anhydrous Potassium Cuprous Thiosulp hate.If 1 part hydrated copper sulphate be added to rather less than 4 parts potassium thiosulphate in hot concentrated aqueous solution, the liquid remains colourless and on cooling a mass of colourless silky needles is deposited. The purification of this salt is attended with some difficulty as although almost insoluble in excess of potas-sium thiosulphate it is very soluble in the cold in pure water. Nor can the substance be reprecipated with alcohol as in this case almost the whole is converted into the yellow modification described above, which separates out in minute hexagonal plates. The needles were therefore freed from mother-liquor by washing them with small quantities of cold water on the filter-pump ; there was considerable loss however. The air-dried substance gave the following results on analjsis corresponding with the formula Cu2S20J,2KLS20J :-Found.Calculated for r-hd-Cu&0,,2K,S,03. I. 11: Cu 20.38 20.65 20.02 Its behaviour with reagents is similar to that of the yellow salt. It does not change colour nor lose weight at 100-110" ; but begins to blacken at 120" with evolution of sulphur dioxide. Barium Cuprozcs Thiosulphate. The colourless and yellow salts both give with barium chloride the same white curdy precipitate of a barium cuprous thiosulphate which dissolves readily in boiling water but is scarcely soluble in cold water. The analyses of the barium salt dried at 100-110" gave results which apparently do not correspond with any simple formula. Found. f-A-, I. 11. x i . Ba 34.08 34-36 33.78 Cu 16.85 S 17.84 - - - -Nos.1 and 2 are analyses of the barium compound obtainedfrom different preparations of the yellow potassium salt ; No. 3 is obtained from the anhydrous white salt. Potassium Silver Thiosutphate. A double tbiosuIphate of silver and potassium has been prepared by Herschel by adding t o a solution of silver chloride in sodium thio 40 HARDEN ON THE ACTION OF SILICON TETRACHLORIDE sulphate a strong solution of potash or a potassium salt. If 2 parts of potassium thiosulphate in solution is added t o 1 part of silver nitrate in solution and boiled a black precipitate of silver sulphide is formed and snlphur dioxide evolved. On the other hand if the FO~U-tion whilst boiling be kept slightly alkaline with pot'assium carbo-nate the amount of black precipitate is very much diminished and the filtrate on standing deposits long colourless transparent prisms of the double salt some of them an inch long. Analyses of the com-pound gave the following results corresponding approximately wilh the formula Ag2S203,2K2S203. Found. --z Calculated for ~ g 2 S O 3 ~ ~ ~ 0 . I. K 22-03 - 22-19 S 27.11 26.62 86-58 Ag 30.50 33-14 33.12 The salt does not lose weight at 100-110" but a few brown specks It is decomposed by acids and alkalis but make their appearance. does not change in the air nor on keeping f0r.a 1eng:th of time