RICHARDS AND BONNET. — DISSOLVED CHROMIC SULPHATE. 15 



plete, the second boiling would produce more acid capable of extraction 

 with alcohol and ether. 



In our experiments a platinum vessel was used for heating the liquid, 

 and the process of boiling and extraction was repeated fourteen times on 

 one sample and twelve times on another. From time to time portions 

 of the green viscous substance were dissolved in water, and two equal 

 portions of the solution were taken for analysis. The chromic oxide was 

 found by evaporation and ignition, the sulphuric acid by precipitation 

 with successive additions of ammonia, baric chloride, and hydrochloric 

 acid in the manner already described. Thus the " atomic ratios " be- 

 tween chromium and sulphuric acid were found. Above are the data 

 and results. The first and the last two analyses were made in duplicate ; 

 the others were each single comparisons. 



Thus the solution became more and more basic as the treatment pro- 

 ceeded. After the eighth extraction a precipitate appeared on each 

 boiling ; this was not filtered off before the ninth analysis, but subse- 

 quently it was removed before each analysis. Before the twelfth boiling 

 in each case a constant ratio was reached, which was not altered by 

 further treatment. This corresponds closely to Crg : (804)0 ; and at first 

 it was supposed that the formula of the compound might be simply 

 CrSO^OH. In order to test this assumption, it was thought desirable to 

 discover if the same equilibriunr could be attained in another way, the 

 second method mentioned at the end of the last section. 



The Treatment of the Green Solution with Chromic 



Hydroxide. 



In order to attain a maximum of dissolved chromic oxide, the pure 

 green solution used above was digested on the steam bath in a platinum 

 dish with pure chromic hydroxide for several hours. A portion was then 

 rapidly filtered, and analyzed, while the remainder was heated for nine 

 hours more. The analyses of the two samples are given on the next page. 



The relation of the chromium to the sulphuric acid in this solution, 

 which had evidently attained a constant composition, was thus found to 

 be essentially like that obtained by extraction with alcohol and ether. 

 The two comparable average results are respectively 1.97 and 1.96, 

 agreeing essentially with the formula CrOHSO^. 



Two circumstances imply that this is not the basic limit of chromic 

 sulphate in cold solutions, however. One of these is the fact that upon 

 extracting such a solution with ether, a clear solution was left which de- 



