276 PROCEEDINGS OF THE AMERICAN ACADEMY 



already been given in Experiment 16; the other yielded 0.8096 

 gram of metal from 2.0350 grains of the sulphate, or 39.78 per cent 

 of copper. 



It is evident that impure cupric sulphate prepared in this manner 

 contains about 39.784 per cent of copper and about 49.838 per cent of 

 ordinary cupric oxide. That is to say, 39.784 parts of copper corre- 

 spond to 10.054 parts of the remainder of cupric oxide. Assuming 

 this remainder to consist solely of oxygen, the atomic weight of copper 

 would be 63.312. But upon comparing the quantity 10.054 with the 

 quantity of sulphuric anhydride found by difference, 50.162, it is 

 evident that a grave error exists in the former figure. This error 

 becomes only more apparent when allowance is made for the occluded 

 acid. 



These inferences are based upon data of somewhat uncertain accu- 

 racy, it is true ; but the error is nevertheless so large as to be appar- 

 ent even to cruder analysis than this. The full explanation of the 

 results, as well as of the variation exhibited by Baubigny's analysis, 

 must be deferred to the next section. The doubts raised by tlie data 

 under discussion formed a useful introduction to the study of cupric 

 oxide. 



III. The Analysis of Cupric Oxide. 



Deprived of the support of the results from cupric sulphate, Hampe's 

 oxide determinations possess little more weight than those of any 

 other experimenter. It will be remembered that the values of the 

 atomic weight of copper deduced from this soui-ce have varied from 

 63.1 to 63.5, Such a fluctuation alone, without the confirmatory 

 evidence which has just been given, is sufficient to cause the suspicion 

 of an undiscovered error in cupric oxide. 



With the hope of detecting the possible error, a number of analyses 

 of the substance were made under varvinjj conditions and with differ- 

 ent samples of material. No difficulty was found in obtaining results 

 varying as widely as those cited above. Part of the cause of this 

 variation was traced to differences in the preparation, and part to 

 differences in the temperature and tension of the surrounding air 

 employed in ignition.* Cupric oxide ignited to constant weight at 

 a very dull red heat lost a very perceptible amount of material upon 



* Compare Bailoy and Hopkins, J. Ch. Son. Trans., 1890, p. 269. Also Schut- 

 zenberger, quotdl in Am J. Sc, [3], XXVI. 05. 



