274 



PROCEEDINGS OF THE AMERICAN ACADEMY 



not, retained when pure sulphuric acid is added to powdered cupric 

 sulphate which has already been nearly dehydrated, but only when the 

 salt is crystallized from strongly acid solutions. This fact rendered 

 the present experiments useless for their original purpose. The re- 

 sults of the two determinations show how insidious constant error 

 may be, if not guarded against by check experiments. 



Synthesis of Cupric Sulphate fkom Metallic Copper. 

 Weights reduced to Vacuum.* 



In order to show that the large differenre between these two aver- 

 ages was due solely to the occlusion of sulphuric acid, the following 

 experiment (No. 42) was made. 3.1227 grams (in vacuum) of the 

 purest crystallized cupric sulphate were dried at 400°, the residue 

 weighing 1.9'J63 grams. The nearly anhydrous salt was then care- 

 fully dissolved in water, and after the addition of small quantities of 

 nitric and sulphuric acids it was evaporated and ignited at a tempera- 

 ture even somewhat higher than before. A gain of 0.0013 gram was 

 apparent, very nearly corresponding to the difference noted above. 

 The acids, tested immediately afterwards, left no weighable residue 

 upon evaporation. 



While it was apparent that these experiments were useless for their 

 original purpose, it was hoped that their comparison with similar 

 syntheses from cupric oxide might furnish valuable indirect evidence 

 with regard to the quantitative relations of the latter imj)ortant sub- 

 stance. The hope was not in vaiu. 



The cupric oxide used as the basis of the three following experi- 

 ments was prepared essentially in the manner described in these Pro- 

 ceedings, Volume XXV., page 199. The three experiments represent 



* Specific gravitj' of Cu = 8.95; of CUSO4 (Hampc and Karsten) - 3.61. 



