ATOMIC WEIGHTS 411 



Schneider himself effected the combustion of manganous oxalate with 

 oxide of copper. The salt was not absolutely dry, so that it was neces- 

 sary to collect both water and carbon dioxide. Then, upon deducting 

 the weight of water from that of the original material, the weight of 

 anhydrous oxalate was easily ascertained. Subtracting from this the 

 COo, we get the weight of Mn. If we put CO, = 100, the quantities of 

 manganese equivalent to it will be found in the last column : 



1.5075 grm. oxalate gave .306 grm. H^O and .7445 grm. CO.. 61.3835 



2.253 " .4555 " 1.1135 " 61.4291 



3.1935 " .652 " 1.5745 " 61.4163 



5.073 " 1.028 " 2.507 " 61.3482 



Mean, 61.3943, ± .0122 



Hence Mn = 54.03. 



Up to this point the data give two distinct values for Mn — one near 

 54, the other approximately 55— and with no sure guide to preference 

 between them. The higher value, however, has been confirmed by later 

 testimony. 



In 1883 Dewar and Scott ' published the results of their work upon 

 silver permanganate. This salt is easily obtained pure by recrystalliza- 

 tion, and has the decided advantage of not being hygroscopic. Two sets 

 of experiments were made. First, the silver permanganate was heated 

 to redness in a glass bulb, first in air, then in hydrogen. Before weigh- 

 ing, the latter gas was replaced by nitrogen. The data are as follows: 



AgMnO,. Ag + MnO. Per cent. Ag + MnO. 



5.8696 4.63212 78.917 



5.4988 4.33591 78.852 



7.6735 . 6.05395 78.894 



13.10147 10.31815 78.756 



12.5799 f -^l^^^ '^-^^2 



1 9.91435 78.811 



Mean, 78.835, ± .0174 



Hence Mn = 55.009. 



The duplication of the last weighing is not explained. 

 In the second series the permanganate was dissolved in dilute nitric 

 acid, reduced by sulphur dioxide, potassium nitrite, or sodium formate. 



1 Proe. Roy. Soc, 35, 44. 1883. 



