1898.] 



of Copper and Sodium. 



245 



of sodium thiosulphate with the application of gentle heat and the 

 sodium hydrate produced was estimated by standard acid, using phenol- 

 phthaliene as an indicator. The result is tabulated below : — 



Weight of Cu 2 used. 



Vol. of standard 



hydrochloric acid 



used. 



Vol. of the standard 

 hydrochloric acid re- 

 quired for 1 gram 

 of the oxide. 



Mean. 



03162 grams. 

 02558 „ 

 0-2928 „ 

 0-2539 „ 



1-7688 „ 



21-7 c.c. 

 174 c.c. 

 20-3 c.c. 

 17 5 c.c. 

 121-9 c.c. 



68-6 c c. 

 68*4 c.c. 

 69-3 c.c. 

 68-92 c.c. 

 6894 c.c. 



68-8 c.c. 



1 c.c. of the standard acid used contained 000734 gram of true 

 hydrochloric acid gas. 



.'. 0"985 grams of real cuprous oxide liberated a quantity of caustic 



soda which required 68*8 c.c. of the standard acid or one gram of real 



., ■ .. L 68-8 x -00734x40 _ B • „ ,. 



cuprous oxide liberates — - Qa . K ^ . OQe , = 0oo2 grams of caustic soda. 



.-. Cu 2 : NaOH : : 



365 x 985 



L ' 562 



' 40 



= 1:2 



= 701 : 1405 



or one molecule of Cu 2 liberates two molecules of sodium hydrate 

 according to the following equation : — 



Cu 2 + H 2 0+Na 2 S 2 3 =2 NaOH + Cu 2 S 2 3 

 The cuprous thiosulphate is kept in solution by the excess of sodium 

 thiosulphate. This solution is very unstable under ordinary circum- 

 stances and black copper sulphide soon separates out. Here we have 

 the explanation of the formation of the black sulphide when the yellow 

 salt is treated with caustic soda. The reaction may therefore be repre- 

 sented by the following equation : — 



7 Cu 2 S 2 3 5 Na 2 S 2 3 16H 2 + 14 NaOH = 12 Na £ S 2 3 + 7 Cu 2 + 23 H 2 0. 

 During the first stage of the reaction the whole of the copper is 

 obtained as cuprous oxide, but the bright redish yellow cuprous oxide 

 being in contact with an excess of sodium thiosulphate in course of 

 time gradually darkens in colour and quite rapidly on heating as the 

 result of the other equation stated above, and subsequent conversion of 

 the cuprous thiosulphate into copper sulphide. It is for this reason 

 again copper cannot be precipitated as oxide by means of caustic soda 

 from a solution containing one mol. of copper sulphate to two or more 

 molecules of sodium thiosulphate. Here we have also the explanation 



