MANGANESE. 283 



This method of von Hauer, which seemed to give good results with 

 cadmium, is, according to Schneider,* inapplicable to manganese, for the 

 reason that the sulphide of the latter metal is liable to be contaminated 

 with traces of oxysulphide. Such an impurity would bring the atomic 

 weight out too high. The results of two different processes, one carried 

 out by himself and the other in his laboratory by Rawack, are given by 

 Schneider in this paper. 



Rawack reduced manganoso-manganic oxide to manganous oxide by 

 ignition in a stream of hydrogen, and weighed the Avater thus formed. 

 From his weighings I get the values in the third column, which repre- 

 sent the MujO^ equivalent to one gramme of water : 



4.649 

 6.8865 

 7.356 

 8.9445 

 11.584 



.0034 



Here the most obvious source of error lies in the possible loss of water. 

 Such a loss, however, would increase the apparent atomic weight of 

 manganese ; but we see that the value found is much lower than that 

 obtained either by Dumas or von Hauer. 



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 

 CO,, 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. 11,0 and .7445 grm. CO,. 61.3835 



2.253 / " .4555 " i-"35 " 61.4291 



3.1935 " .652 " 1.5745 " 61.4163 



5.073 '< 1.028 " 2.507 '♦ 61.3482 



Mean, 61.3943, ± .0122 



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 f 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 



* Poggend. Annalen, 107, 605. 

 t Proc. Roy. Soc, 35, 44. 1883. 



