COLOKIMETRIC ESTIMATION OF NICKEL AND COBALT. 409 



As it is proposed to apply the method of estimation to 

 the mixed metals deposited by electrolysis and nitric acid 

 is the most suitable solvent, nitrate solutions of both cobalt 

 and nickel were prepared and used in the subsequent experi- 

 ments; it is also assumed in all cases that the sum of the 

 weights of Ni and Co present are known. 



The measuring vessels used in the preparation of Ni(N0 3 ) 2 

 and Co(N0 3 ) 3 solutions of accurate strength were all cali- 

 brated at 15° 0. 



Preparation of Solutions. 



Ni precipitated by electrolysis from Co free NiS0 4 (Kahl- 

 baum's) 



Co first precipitated as cobaltinitrite from Oo(N0 3 ) 2 

 which was found to contain a trace of Ni, followed by solu- 

 tion in H 2 S04, addition of NH 4 0H and (NH 4 ) 3 S04 and 

 electrolysis. 



The precipitated metals were dissolved in HN0 3 , evapor- 

 ated over waterbath almost to dryness, dissolved in water 

 and diluted to definite volume. 



Ni(NQ 3 ) a ~ solution 

 Jt o 



2*7366 grams of Ni in 234*7 cc. water 



*01166 grams of Ni in 1 cc. water 



Oo(N0 3 ) 2 y- solution 



'6973 grams of Co in 119*07 cc. water. 

 '005856 grams of Co in 1 cc. water. 



Standard. 

 The preliminary experiments showed *05- *06 gm. of the 

 mixed metals to be the maximum amount permissible in 

 solution to produce a suitable neutral tint, stronger solu- 

 tions were of a drab tint and prevented a sharp change 

 being noticed. The solution of standard tint was made as 

 follows : — 



