184 



Dr. E. J. Mills and J. J. Smith. [June 19, 



phate, was boiled with hydric chloride until dissolved. Water was 

 then added, and the lead precipitated with hydric sulphate and alcohol. 

 The filtrate from the plumbic sulphate was then evaporated to dryness, 

 heated till the excess of hydric sulphate was driven off, and dissolved 

 in water. A little hydric sulphide was then added, to remove a small 

 quantity of lead still present, the filtrate evaporated to dryness, and 

 the cobaltous sulphate weighed. The plumbic peroxide must, of 

 course, be perfectly pure, because any impurity in it finds its way into 

 the cobalt, and consequently makes that result too high. 



In an experiment with this process, *2500 grm, of cobaltous 

 sulphate, and "2500 grm. nickelous sulphate were taken, and the 

 quantities found after the separation were "2505 grm. cobaltous 

 sulphate, and "2490 grm. nickelous sulphate. The estimation of 

 the cobalt is rather a troublesome and tedious process ; but when 

 the mixture of nickel and cobalt can be weighed, and the nickel in it 

 estimated, the cobalt being taken by difference, this is an admirable 

 method to employ. The following are some results of the estimation 

 of the nickel in a mixture of '2500 grm. of cobaltous sulphate and 

 '2500 grm. of nickelous sulphate. 



Nickelous sulphate taken. Found. 



(1.) '2500 -2480 



(2.) „ '2505 



(3.) „ -2490 



(4.) „ '2495 



(5.) „ -2480 



Mean.... -2490 

 Probable error of a single determination 0'16 per cent. 



III. 'Experiments on Equivalence. 



Having then fixed on the method of separation, 1 per cent, 

 solutions of nickelous and cobaltous sulphates were prepared, and a 

 solution of sodic hydrate, of which 10 cub. centims. were capable of 

 precipitating '8248 grm. of nickelous or cobaltous sulphate. This 

 sodic hydrate was made from sodium, and kept in glass bottles coated 

 internally with a thick layer of paraffin. 



A series of nine experiments was made, in which the relative 

 weights of nickelous or cobaltous sulphate present, varied from '1 to 

 •9 grm. ; the total weight of nickelous and cobaltous salt, and the 

 volume of the solution being, however, always the same, viz., 1 grm. 

 and 100 cub. centims. The experiments were conducted as follows : — 

 The bottles containing the solutions of the sulphates and the sodic 

 hydrate were immersed in a trough into which there was a constant 

 flow of water to bring them to a constant temperature. The necessary 



