ATOMIC WEIGHTS 



413 



he threw down the hydrated peroxide electrolytically, and the latter com- 

 pound was then reduced in hydrogen which had been proved to be free 

 from oxygen. The resulting monoxide was cooled in a stream of purified 

 nitrogen. After the oxide had been treated with sulphuric acid, con- 

 verted into sulphate, and weighed, a few drops of sulphuric acid and 

 a little sulphurous acid were added to it, after which it was reheated and 

 weighed again. This process was repeated until four successive weighings 

 absolutely agreed. The results of this set of experiments were as follows, 

 reduced to a vacuum standard : 



Mean, 47.002, ± .0006 



Hence Mn = 55.008. 



Marignac's mean, combined with this, hardly affects either the per- 

 centage itself or its probable error. Fortunately, both Marignac and 

 Weeren are completely in agreement as to the ratio, and either set of 

 measurements would be valid without the other. In order, therefore, to 

 give Marignac's work some proper recognition, we can assume a general 

 mean of 47.004, ±.0006, without danger of serious error. 



The manganese sulphate produced in the foregoing series of experi- 

 ments was used, with many precautions, for the next series carried out 

 by von Hauer's method. It was transferred to a porcelain boat, dried at 

 260° to avoid errors due to retention of water taken up in the process of 

 transfer, and then heated to constant weight in a stream of hydrogen 

 sulphide. Before weighing, the sulphide was heated to redness in hy- 

 drogen and cooled in the same gas. The results, with vacuum weights, 

 were as follows : 



Mean, 57.633, ± .0004 

 von Hauer found, 57.608, ± .0080 



Hence the general mean is identical with Weeren's to the third deci- 

 mal place, which is unaffected by combination with von Hauer's data. 

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