OF ARTS AND SCIENCES. 213 



In this connection it is worthy of notice that II. Baubigny,* a recent 

 experimenter upon the atomic weight of copper, dried cupric sulphate 

 ut 410° without evidence of the formation of basic salt, and from the 

 weight of copper oxide produced by the ignition of this salt obtained 

 the value 63.47 for the constant under discussion. Baubigny's experi- 

 ments are too briefly described to be fairly discussed, but their evi- 

 dence agrees with that of the results of Shawf in pointing toward 

 a higher value of the atomic weight of copper than that usually ac- 

 cepted. 



In the critical review of the present investigation it must be remem- 

 bered that three distinct methods have been used, the last two being 

 united for the sake of convenience. The chief probable constant error 

 in the first series, given in the two preceding papers, is the chance of 

 a secondary reaction between the copper and the argentic nitrate ; but 

 the purity of the silver produced, the absence of the slightest gas evo- 

 lution during the progress of the chemical action, and the total lack of 

 effect of dilution upon the final result, alike point to the conclusion 

 that no such secondary action took place. In the research upon cupric 

 bromide the chief probable constant error which could raise the ob- 

 served atomic weight of copper is the presence of basic salt in the solu- 

 tion, but the final crystallization of a neutral salt from an acid solution 

 makes this chance very unlikely. Moreover, the basic salt was shown 

 to be perfectly insoluble in water, and a direct experiment with methyl- 

 orange proved the solution to be normal. 



While no experimental knowledge can be said to be even relatively 

 certain, and these with all other results are submitted only to be re- 

 vised, and perhaps changed, by later experimentation, careful thought 

 seems to show that the presumption is now upon the side of the later 

 determinations of the atomic weight of copper. 



During the last few years the atomic weights of antimony t and of 

 cadmium § have also been determined in this Laboratory, and have 

 been referred to the same elements as those used in the present work. 

 A statement of the final comparison might not be uninteresting. 



Ag : Br : Sb : Cd : Cu = 108.00 : 80.00+ : 120.00 : 112.31 : 63.64. 



The collective results of the research must now be referred to the 

 various different units of atomic weight usually adopted. Recently, 



* Compt. Rend., xcvii. 854, 906. 



t Pliil. Mas?., 5th Series, xxiii. 138. 



t J. P. Cooke, lor. cit. 



§ O. W. Huntington, these Proceedings, xvii. 28. 



