OF AETS AND SCIENCES. 



259 



great power of occluding many salts, but few experimenters seem to 

 have realized that the occlusion of most metallic sulphates tends to 

 decrease the amount of precipitate obtained. This fact was recognized 

 by Professor Jannasch and the writer* in 1889, and would influ- 

 ence the controversy between Ostwaldf and Kruss.J The occlu- 

 sion of baric chloride of course increases the amount of precipitate 

 when sulphuric acid is to be determined, and diminishes it when 

 barium is to be determined. With care this last error may be reduced 

 to a very small amount, but it is doubtful if it has ever been wholly 

 avoided. A trace only of copper was found in the precipitate ob- 

 tained in the experiment described above, showing that cupric chloride 

 is not occluded to any essential extent. 



In spite of the fact that the important analyses of the third series 

 were far more carefully performed than those of the second, the result 

 was no more satisfactory than before. It was therefore apparent that 

 a point had been reached beyond which further refinement was unavail- 

 ing, and that the reason of the discrepancy must be sought, not in 

 accidental or variable impurity, but rather in some property inherent 

 in the purest cupric sulphate. 



Analysis of Cupric Sulphate. — Third Series: Data. 

 Weights reduced to Vacuum Standard. 



* J. fiir prakt. Chemie, XXXIX. 321 (1889). 

 t Lehrbuch der Allgem. Chem., I. 53. 

 1 Annalen, CCLXII. 40. 



