Dr Thomson an the atomic weight of Nickel. 157 



dissolved, while the oxide of cobalt remains behind in the state 

 of a hydrate, and still retaining mixed with it a certain pro- 

 portion of oxide of nickel. 



The muriate of nickel thus purified was converted into sul- 

 phate in the usual way. The solution was concentrated, and 

 left to spontaneous crystallization. 



I consider sulphate of nickel made in this way to be quite 

 pure. It contained no trace of arsenic, copper, cobalt, bis- 

 muth, or antimony, the only foreign metals which I have 

 been able to discover in speiss. Having thus obtained pure 

 sulphate of nickel, let us proceed to the analysis of the salt. 



1st, 34.25 grains of the crystals were dissolved in as small a 

 quantity of distilled water as possible ; 26.5 grains of recent- 

 ly ignited chloride of barium were separately dissolved in a 

 minimum of distilled water. 



These two solutions were mixed, the mixture placed on the 

 sand-bath, together with the washings, and evaporated till the 

 whole was reduced to about an ounce measure. It was then 

 thrown upon a filter. The clear liquid which passed through 

 was tested in the usual manner for sulphuric acid and bary- 

 tes ; but no trace of either of these two substances could be 

 found in it. Hence the barytes from 26.5 grains of chloride 

 of barium had just saturated the sulphuric acid in 64.25 grains 

 of sulphate of nickel, — that is to say, 34.25 grains of sul- 

 phate of nickel contains just ten grains of sulphuric acid. * 



2d, 34.25 grains of the same crystals of sulphate of nickel 

 were cautiously heated over a spirit lamp in a small platinum 

 crucible, raising the heat very slowly as the water evaporated, 

 till at last the salt was brought into a state of dull but percep- 

 tible ignition. It was kept in this state till it ceased to give 

 out any more aqueous fumes, and then weighed. The loss of 



• I collected the sulphate of barytes thus formed. After edulcoration 

 and ignition it weighed 29 grains. But as 10 grains of sulphuric acid re- 

 quire for saturation 1 9.5 grains of barytes, there is a deficiency amounting 

 to half a grain. The reason of this deficiency was this. When I was ad- 

 justing the filter on which the dry sulphate of barytes had been collected, 

 in order to make it as nearly as possible of the same size as the filter in 

 the opposite scale, a piece of the sulphate of barytes sprung out and fell 

 upon the floor. I have no doubt that this piece amounted to half a grain, 

 though I was unable to collect it. 



