240 



PROCEEDINGS OF THE AMERICAN ACADEMY 



XV. 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 



HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OF COPPER. 



FOURTH PAPER. 



By Theodore William Richards. 



Presented June 10, 1891. 



Table of Contents. 



PAGS 



Introduction 240 



Balance and Weiglits 242 



I. Analysis of Cupric Sulphate . . 244 



Materials 245 



Description : Three Series . . 249 



Cause of the Deficiency . . . 260 



Atomic Weight of Sulphur . 268 



Atomic Weight of Copper . . 270 



II. 

 III. 



IV. 

 V. 



Sj'nthesis of Cupric Sulphate 

 Analysis of Cupric Oxide . 

 Tests for Impurities . . 



PAGE 



273 

 27tj 

 278 



Determination of Occluded 



Gases 281 



Upon Typical Copper . . . 291 



Summary of Results .... 293 



Introduction. 



It will be remembered that recent investigation upon the atomic 

 weight of copper has pointed toward the existence of a value for that 

 constant very different from the one indicated by earlier determina 

 tions. During the winter of 1886-87 a number of experiments * were 

 made in this Laboratory upon the replacement of silver from solutions 

 of argentic nitrate by means of metallic copper; and during the follow- 

 ing winter these were supported by similar series t involving material 

 from different sources. The consistent verdict of all these experi- 

 ments indicated a considerably higher atomic weight than that which 

 had previously been accepted ; but although the new method seemed 

 to be in every way satisfactory, the presumption must nevertheless re- 

 main in favor of the older value until the presentation of more evi- 



* These Proceedings, XXII. 342. 



t These Proceedings, XXIII. 177 ; Fres. Zeitschr., XXVIII. 392. 



