252 PROCEEDINGS OF THE AMERICAN ACADEMY 



Grams. 



Weight of crucible + CUSO4 . 5 HgO = 23.36188 



" " alone = 20.30300 



" cupric sulphate in air := 3.05888 



Correction to vacuum (Sp. gr. = 2.274) = .00118 



Corrected weight CUSO4 . 5 HgO, iu vacuum = 3.06006 



Weight crucible + CUSO4 dried for three hours at 255° = 22.26243 

 " " dried for two hours more = 22.26233 



The crucible and contents gained in weight upon the balance pan 

 at a rate of only one tenth of a milligram in four minutes, and hence 

 the last weighing is without doubt sufficiently accurate. When the 

 weight had thus become constant, twenty drops of strong pure sulphu- 

 ric acid were added to the white powder, and the whole was kept at a 

 temperature of 365° for three and one half hours in a suitable air bath 

 composed of a nest of porcelain crucibles. An air thermometer was 

 used in measuring the temperature. 



Grams. 



Weight of crucible and contents = 22.25905 

 The same, after reheating for four hours with six drops 



more of 11.^0^ = 22.25900 



Weight in air of cupric sulphate dried at 365° = 1.95600 



Weight in vacuum of cupric sulphate (Sp. gr.* = 3.61) = 1.95637 



Loss of weight between 255° and 365° = .00333 



The crucible and contents gained in weight even less rapidly than 

 before. 



This experiment shows that the so-called anhydrous cupric sulphate 

 of Hampe loses about seventeen one-hundredths of a per cent of its 

 weight when subjected to the temperature of the boiling point of mer- 

 cury ; a loss nearly equal to the deficiency which we are seekinj; to 

 explain. The residual salt may be slowly dissolved in water without 

 the need of very great caution. It gives a perfectly clear solution, 

 which is neutral to methyl orange and does not deposit basic salt even 

 upon indefinite standing. These facts alone show that the decrease 

 in weight was not due to loss of acid, but a much more definite proof 

 of this point is given later. 



For electrolysis, the clear solution of the 1.95637 grams of cupric 

 sulphate was transferred to a large platinum crucible. This crucible 

 had been previously coated inside with pure copper, washed with 



* Tliis is a mean of the results of Hampe and Karsten. 



