Nitrogen Thermometer from Zinc to Palladium. 155 



ammonium persulphate was added and a stream of air passed 

 through the solution for some time. No manganese. 

 Fe 2 3 = 6*1 mg., after repeated precipitation. Fe = 4*2 mg. 

 Repeated efforts were made to separate zinc with H 2 S on the 

 principle of the lower solubility of ZnS in dilute acids, but 

 without satisfaction. First I tried to precipitate a small fraction 

 of the nickel, hoping to get all the zinc with it. The volume 

 of the solution was about 5 1. But unless so much acid was 

 added that strong doubts were entertained of recovering any 

 zinc that might be present, the fraction of the nickel precipi- 

 tate was far too great. Again, all the nickel was precipitated 

 and the precipitate was digested with cold 10 per cent solution 

 of hydrochloric acid. Here one had to fear either the failure 

 to remove the zinc or the removal of too much nickel to handle 

 without so many precipitations that a small quantity of zinc 

 would probably be lost. It is doubtful whether we have any 

 method which will give very small amounts of zinc in metallic 

 nickel. 



The whole solution was now tested for cobalt as follows : 

 It was freed from H 2 S by evaporation, acidulated with HC1 

 and precipitated by a-nitroso-yS-naphthol in 50 per cent acetic 

 acid. This was added in several portions. After long stand- 

 ing the precipitate was collected and washed. The voluminous 

 precipitate was very cautiously burned in a capacious porce- 

 lain crucible. Much tar was formed. The residual oxide was 

 dissolved in nitric acid and the cobalt separated from nickel 

 by KN0 2 in the usual way. The potassium cobalto-nitrite 

 was finally decomposed by sulphuric acid and precipitated 

 electrolytically from ammoniacal solution. Co = 101*4 mg. + 4*9 

 mg. recovered from filtrate and weighed as sulphate. Total = 

 0*1063 per cent. Fe and Co were also determined in a separate 

 10 g. portion of metal. Fe 2 3 = 0*7 mg. Fe =■ 0*49 mg. — 

 0*0049 per cent. Co = 10*3 mg. = 0*1030 per cent. A 

 separate 10 g. portion was taken for sulphur. It was dissolved 

 in nitric and evaporated on the water bath. This solution was 

 diluted and precipitated with a slight excess of sodium car- 

 bonate. The filtrate was just acidulated, evaporated, and 

 treated with barium chloride. JSTo precipitate. 



Analysis of Nickel. 



Au 



none 



Bi 



none 



Pt 



-0023^ 



Cd ___. 



a 



As 



none 



Zn____ 



none found 



Sb 



a 



Co ____ 



-1063^ 



Sn 



u 



Mn ... 



none 



Pb 



-0001^ 



Fe .... 



-0042^ 



Cu 



-0523^ 



S 



none 



•165% 



