OP ARTS AND SCIENCES. 



265 



been heated enough. This result is hence probably too low. Tlie 

 last experiment was more carefully regulated, and is more trustworthy. 

 In this case the cupric sulphate was heated for an hour at very dull 

 redness. 



Action of Heat upon Cdpric Sulpuate. 



Weights reduced to Vacuum. 



The filtrates from the preciftitates of basic salt did not deposit any 

 further solid upon long standing. That from the last determination 

 was rendered very distinctly acid to methyl orange by the addition of 

 a milligram of sulphuric acid, in spite of the difficulty in detecting the 

 color-change in the presence of the blue cupric sulphate. These tests 

 indicate that the filtrate was wholly normal. 



In order to test still more definitely the accuracy of the method, 

 the following mode of procedure was devised. To neutral solutions 

 of cupric sulphate — prepared either from the purest crystals or by 

 long standing after the neutralization of the trace of acid in ordinary 

 " chemically pure " material — were added small measured amounts 

 of a standard sodic hydroxide solution. After a time, the precipitate 

 was filtered oft' and dissolved in standard sulphuric acid, exactly as 

 if it had been obtained by the expulsion of the acid through heat. 



* See page 266, Experiments 26-37. 



