M. R. Schneider on the Equivalent of Manganese. 271 



looked forward to with anxiety. In a later communication*, 

 however, instead of the proof for the number 26, we find the 

 equivalent of manganese placed among the numbers which re- 

 present, it is said, simple multiples of half an equivalent of hy- 

 drogen ; namely we find its equivalent given as 27*5, that is, one 

 and a half hydrogen units higher than before. 



The inaccuracy of the number 26, Dumas now (in his latest 

 complete memoir on the equivalents of the simple bodies)t seeks 

 to explain by the supposition that a part of the suboxide of 

 manganese may have been reduced to manganese. According 

 to my observations (p. 269) this is very improbable; on the 

 other hand, I imagine that Dumas has far undervalued the dif- 

 ficulties attending the preparation (according to Berthier's me- 

 thod) of a peroxide of manganese having exactly the composition 

 indicated by the formula. Without dispute it was dangerous to 

 choose, for the basis of operation of an equivalent determination, 

 a body which gives up its water only a little below its tempera- 

 ture of decomposition while at the same time its normal quantity 

 of oxygen is confined between very naiTow limits of temperature. 



The experiments of Dumas, from which the number 27*5 is 

 obtained as the equivalent of manganese, were performed by 

 the same method that Berzelius employed ; i. e. the amount of 

 silver was determined necessary to precipitate a known quantity 

 of anhydrous subchloride of manganese. I cannot admit for 

 this method that degree of accuracy which Dumas appears to 

 claim for it. In other places I have already declared that I do 

 not consider the choice of metallic chlorides as a basis for equi- 

 valent determinations a very happy one, because many of these 

 substances are very hygroscopic, and, at the temperature to 

 which it is necessary for them to be exposed for complete dehy- 

 dration, they are extremely inclined to take up oxygen, partly 

 from the air, partly from the partial decomposition of the water 

 they have taken up. This is the case with subchloride of man- 

 ganese to a greater extent than with many other subchlorides. 



Partly on account of the dou])t just expressed concerning the 

 accuracy of the methods employed by other chemists in the de- 

 termination of the equivalent of manganese, partly on account 

 of the wish to decide whether in the series of experiments first 

 described a considerable error of observation had crept in, I 

 resolved to determine the equivalent of manganese myself. In 

 doing this I have pursued a method similar to that which 1 fol- 

 lowed in determining the equivalents of nickel and cobalt ; that 

 is, I have endeavoured to determine with the greatest accuracy 



* Comptes Hindus, vol. xlvi. p. 951. Ann. der Chem, und Pliarrn. 

 vol. cviii. I). .324. 



t Ann.'de Cliim. et de Phys. (3) vol.lv. \u 129. 



