242 C. B. and J. B. Bhaduri — On Double Thiomlpliates [No. 1, 



brown in the course of a few minutes, and finally deposited a dark-brown 

 precipitate readily soluble in water. If, however, thoroughly saturated 

 solutions of both copper sulphate and sodium thiosulphate, previously 

 heated to about 50-60°C, be used, similar yellow crystaline precipitate 

 is obtained which settles down easily. Care should however be taken 

 in washing the salt, as a comparatively large quantity of sodium 

 sulphate is formed in this case which has to be removed. But the 

 freshly precipitated salt is also sensibly soluble in water. It should 

 therefore be drained as completely as possible, washed once or twice 

 with water and then with dilute alcohol gradually increasing the 

 strength of alcohol and finally with alcohol alone. Different samples 

 have been thus prepared with slight modification in the process, and the 

 result of the analysis of the same are included in the annexed table. 

 On examination it will however be found that although the samples 

 appear to be identical in physical properties, they all differ more or less 

 m composition and that therefore different formulae should be given 

 to them. (See Table p. 243). 



As we had reason to believe that the percentage of sodium in F 

 was a little too high the atomic ratio appears to be as Cu : Na : S : O : 

 H 2 = 4 : 3 : 7 : 16 : 6 corresponding to the formula 4 Cu 2 S 2 3 , 3 Na 2 

 S 2 3 9 H 2 0. With the following percentage composition : — 



Cu=31-84 % S=28-17 % „ Q ,„ 0/ 



Na = 8-68 % O = 32-20 % 2 /o 



In E the ratio of copper to sodium is as 7 : 6. 



By heating therefore with sodium thiosulphate a part of copper is 



separated, thus increasing the percentage of sodium and sulphur. But 



whether at any particular temperature a compound of perfect definite 



composition is formed or not, it is impossible to say positively. 



We next proceeded to consider what takes place when copper acetate 



is used instead of copper sulphate, thinking that acetic acid being a 



weaker acid might give the normal copper thiosulphate or the acid salt 



of V. Hauer. Copper acetate is less soluble in water than copper 



sulphate, and accordingly we had to work with comparitively dilute 



solutions. Thinking that concentration and relative proportion might 



produce corresponding difference in composition standard solutions of 



N 

 copper acetate and sodium thiosulphate (I c.c. Thio. = 10'835. — Thio. = 



10835 x "0248 gms. Thio. = -2687 gms. and 1 c.c. copper acetate = 

 '0182 gms. Cu) were prepared. Kessel and Vortmann state that the 

 yellow salt described by them can only be obtained when the two solu- 

 tions are mixed in the ratio of one molecule of copper salt to two 



