1883.] 



On the Atomic Weight of Manganese. 



47 



the improbability of its containing excess of any of the elements of 

 which it is composed beyond what is necessary for the formation of 

 the normal componnd, recommend it especially for this purpose. 

 Another point which rendered its selection important was to ascertain 

 if a body liable to partial decomposition nnder certain circumstances 

 could give concordant results in atomic weight determinations, thus 

 putting to a crucial test the amount of variation in the values which 

 may be attributed to secondary causes. 



Table II gives the results of the titrations. The use of sulphurous 

 acid as the reducing agent was found unsatisfactory, as a slight 

 residue having the appearance of sulphide was almost always left 

 undissolved. The production of sulphate was also more or less 

 troublesome from its insolubility. 



Table II. 







AgMn0 4 . 







KBr. 



Equiva- 





No. 



AgMn0 4 . 



Corrected 





KBr. 



Corrected 



lent of 



Reducing agent. 





for vacuo. 







for vacuo. 



AgMn0 4 . 





1 



6 -528 



6 -5289 



3 



•4228 



3 42385 



227-091 



Sulphurous Acid. 



2 



7 -5368 



7 -5378 



3 



•9541 



3-9553 



226 -958 



Nitrite of Potash. 



3 



6 -1000 



6 -1008 



3 



•20067 



3 -20166 



226-937 





4 



5 -7457 



5 -74647 



3 



•00581 



3 -00677 



227 -606 



Sulphurous Acid. 



5 



6 '1651 



6 -16593 



3 



•23503 



3 -23602 



226 918 



Formate of Soda. 



6 



5-1126 



5 -11329 



2 



•68216 



2 -6828 



226 -984 



Nitrite of Potash. 



7 



5 -0737 



5 -07438 



2 



•6614 



2 -66204 



227-013 



8 



13 -4466 



13 -4484 



7 



•05385 



7 -05602 



226 -983 



Hydrogen. 



9 



12 -5782 



12 -5799 



6 



•59861 



6 -60065 



226 -972 



10 



12 -2686 



12 -27025 



6 



•4361 



6 -43808 



226 -976 



Nitrite of Potash. 



Experiments (6) and (7) were made with a sample obtained from 

 the barium salt, and these results are slightly higher owing to the 

 presence of a small trace of barium sulphate easily recognisable by 

 the slight turbidity of the reduced solution. We had hoped by the 

 use of a larger quantity of material to arrive at results comparable 

 in some degree at least with those of Stas ; but we found the pre- 

 paration of considerable quantities of material of absolute purity fre- 

 quently involves sources of error not incurred in the production of 

 smaller quantities. This we observed especially in the preparation of 

 our pure potassium bromide, which contained traces of sulphates in 

 every sample. This sulphate is due to the use of ordinary gas in the 

 ignition of the pure bitartrate of potash from which the bromide of 

 potassium was made. In order to get a pure product gas must be 

 replaced by a powerful flame of alcohol, or all the operations conducted 

 in a muffle. 



The mean atomic weight of manganese which results from the 



