158 PROCEEDINGS OF THE AMERICAN ACADEMY. 



VIII. 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OF ZINC. 



FIRST PAPER : THE ANALYSIS OF ZINCIC BROMIDE. 



By Theodore William Richards and Elliot Folger Rogers. 



Presented April 10, 1895. 

 Table of Contents. 



PAGE 



IntroducUon 158 



Balances and Weights 102 



The Specific Gravity of Ziucic Bro- 

 mide 102 



PAGE 



Preliminary Analyses of Zincic 



Bromide 163 



Final Series of Determinations . . 170 



The Atomic Weicht of Zinc ... 179 



Introduction. 



In an account of a recent investigation on the occlusion of gases by 

 the oxides of metals * it was shown that zincic oxide, in common with 

 cupric and magnesic oxides, has the power of retaining important 

 quantities of oxj'gen and nitrogen gases, even at very high tempera- 

 tures. Hence it was evident that all determinations of the atomic 

 weight of zinc depending upon the conversion of the metal into the 

 oxide through the ignition of the nitrate must be influenced by a con- 

 stant error, whicli has the tendency to make the results lower than 

 the true value. In consideration of this fact, it becomes very impor- 

 tant to review all of the results thus far obtained regarding the atomic 

 weight of zinc, in order to determine how seriously the error in ques- 

 tion may influence our accepted value. A chronological listf of the 

 accessible data is given below. 



* These Proceedings, XXVIII. 200, Richards and Rogers. 



t Much assistance in preparing the list has been obtained from the works of 

 Clarke, Meyer and Seubert, and others. The results have been recalculated 

 with the assumption of the following atomic weights: = 16, C = 12.002 

 CI = 35.456, Aq = 107.98, H = 1.0075. 



