264 PROCEEDINGS OP THE AMERICAN ACADEMY 



Experiments showed that between 360° and 400° cupric sulphate 

 does not essentially lose in weight. For example (No. 19 or 23), 

 1.28563 grams of the substance dried at the former temperature 

 weighed 1.28558 grams after heating for ten hours at 400°. At the 

 temperature of dull redness the salt slowly decomposes. 



If the loss of weight during this decomposition could be compared 

 with the deficiency of sulphuric acid in the residue, it is evident that 

 an indirect means would be at hand for the detection of a possible 

 simultaneous loss of water. Such a circuitous road seemed to be the 

 only one open to the present search. 



In the series of experiments tabulated below, pure cupric sulphate 

 was heated in the usual manner to 250°, and then after the addition of 

 sulphuric acid to 400°, until the salt became constant in weight. The 

 heat was then increased to dull redness, and after cooling the loss of 

 weight was determined. Upon solution of the residue in water a small 

 amount of basic salt was naturally deposited. Since the filtrate was 

 apparently quite normal, it is evident that the amount of sulphuric 

 acid necessary exactly to dissolve this precipitate must have been 

 equivalent to the anhydride driven off. 



After standing a considerable time, the basic salt was carefully 

 filtered off and a measured amount of twentieth normal acid was used 

 for its solution. The crucible used for the ignition was also washed 

 with a measured quantity of acid. The clear solutions were all com- 

 bined, and the excess of acid was determined by sodic hydroxide and 

 methyl orange. Since the loss of weight upon ignition was noticeably 

 more than the amount of anhydride corresponding to the quantity of 

 sulphuric acid used to dissolve the basic salt, something beside sulphur 

 trioxide must have been expelled by the heat. 



The last column of the table gives the difference between the loss 

 of weight of the cupric sulphate and the amount of sulphuric anhy- 

 dride required to dissolve the basic salt, expressed in percentage of 

 the original crystallized compound. This difference probably repre- 

 sents a small amount of water held even at 400°. The results showed 

 a very noticeable variation, and at first sight appeared somewhat un- 

 satisfactory. The first two experiments agreed well with each other, 

 and were apparently very trustworthy. In the third, on the other 

 hind, the amount of basic salt was so large as greatly to interfere 

 with the accuracy of the result. In Experiment 23 the lossr of weiglit 

 upon ignition was so very large, amounting to about three per cent of 

 the anhydrous sulphate, that the experiment was rejected. After 

 such a failure, it was natural that the next sample should not have 



