266 



PEOCEEDINGS OF THE AMERICAN ACADEMY 



Test of Mkthod. 

 Precipitation and Solution of Basic Citpric Sulphate. 



It is hence evident that from dilute solutions the basic salt is wholly 

 precipitated in a comparatively short time. Even under the worst 

 conditions no deficiency approaching that noticed in Experiment 25 

 was observed. Another series (Experiments 34-37), made in very 

 dilute solutions without filtering, gave values for the factor which 

 respectively equalled 0.97, 0.98, 0,95, and 0,98. The average is 

 0.97, not seriously different from that found above. The first value 

 of the factor was used in correcting the results of Experiments 20-25. 

 Tlie correction involved is extremely slight except in Experiment 22, 

 where the application of the full value of the factor to a very large 

 quantity is of doubtful advisability. Hence it is better to omit this 

 experiment from the final average. 



One contingency alone is not provided for by these test experiments 

 that is to say, the formation of a cuprous compound and its solution in 

 the cupric salt. The formation of a cuprous salt by gentle ignition of 

 cupric sulphate in the air is far from probable ; but for fear that such 

 a reaction had taken place, the solution of the cupric sulphate was 

 usually exposed to the air from twelve to twenty-four hours before 

 filtration. The fact that exposure to the air for a long time after 



