in a Recalculation of the Atomic Weights. 109 



Secondly, confusion arises from the fact that many of the 

 weighings under discussion were not reduced to the standard 

 of a vacuum ; while others had been subjected to such a cor- 

 rection. The errors thus introduced into the calculations are 

 small, but still they cannot be lost sight of. 



Another set of errors of unknown magnitude are produced 

 as follows : — Many series of experiments, notably in the work 

 of Stas, Marignac, and other eminent investigators, involve 

 the titration of chlorides, bromides, or iodides with solutions 

 containing known weights of metallic silver. But Dumas 

 has lately shown that silver, purified after the usual methods, 

 occludes weighable quantities of oxygen. In other words, the 

 silver hitherto employed in atomic- weight investigations has 

 not been pure silver. One exception is found in Mallet's re- 

 search upon aluminum. Since the atomic weights of nearly 

 all the elements depend directly or indirectly upon silver, this 

 source of error becomes of the gravest importance. Analogous 

 errors may possibly occur with metals other than silver, and 

 should be carefully looked for. For example, the atomic 

 weights of both copper and oxygen depend upon the reduction 

 of copper-oxide in hydrogen. If the residual copper, which is 

 weighed, occludes any hydrogen, then the atomic weight of 

 copper will come out too high, and that of oxygen a trifle too 

 low. Such an error might account for the difference of be- 

 tween 15*9633 and 16 in the case of oxygen. 



In connexion with the data discussed in this investigation, 

 it is perhaps worth while to consider the bearing of the results 

 upon Prout's famous hypothesis. In order to simplify 

 matters I tabulate the new atomic-weight values in two 

 columns, one containing numbers referred to hydrogen as 

 unity, the other with figures comparable with oxygen as equal 

 to 16. 



Table of Atomic Weights. 



Hydrogen .. 

 Fluorine .. 

 Chlorine . . 

 Bromine .. 



Iodine 



Lithium 



Glucinum . . 

 Magnesium 



Zinc 



Sodium 



Potassium . . 

 Rubidium .. 



H=»l. 



0-16. 



1-0000 



1-0023 



18-984 



19027 



35-370 



35-451 



79-768 



79-951 



126-557 



126-848 



7-0073 



7-0235 



9 085 



9-106 



23-959 



24.014 



64-905 



65-054 



22-998 



23-051 



39019 



39-109 



85-251 



85-529 [I 





11 = 1. 



= 16. 



Caesium 



132-583 



132-918 



Silver 



197-675 

 203-715 



107023 

 204183 



Thallium ... 



Phosphorus 



30-958 



31029 



Vanadium. . . 



51-256 



51-373 



Arsenic 



74-918 



75-090 



Cadmium ... 



111-770 



112027 



Mercury ... 



199-712 



200171 



Calcium . . . 



39 990 



40082 



Strontium... 



87-374 



87-575 



Barium 



136-763 



137-007 



Lead ......... 



206-471 



206-946 



