Royal Society. 219 



For the determination of the equivalent of manganese, sul- 

 phate of manganese was used, which had been prepared from a 

 specimen of fine crystallized pyrolusite from Bohemia. The 

 sulphate was obtained perfectly neutral and pure without any 

 great difficulty. For its reduction, however, a somewhat 

 higher temperature than that of a lamp was required, and the 

 glass tube was accordingly changed for a porcelain tube, which 

 was heated to redness in a Liebig's combustion furnace, and 

 the gas was passed through under a slightly increased pressure, 

 in order to bring it more fully in contact with the salt to 

 be reduced. As in the former case, the reduction vvas com- 

 menced at a low temperature, which was then gradually increased. 

 The sulphide of manganese obtained is considerably caked toge- 

 ther, is of a dark green colour, and not in the slightest degree 

 hygroscopic. The mean of nine very concordant experiments was 

 27-4906, which is sufficiently near 27-5 to allow the assumption 

 of that number. The numbers obtained by Berzelius were re- 

 spectively 27"5 and 27'61. 



Subsequently, v. Hauer tried to determine the equivalent by 

 reducing the red oxide of manganese to protoxide by means of 

 hydrogen. Unfortunately, the loss of weight in this case is 

 very small. This objection may be easily obviated by employing 

 large quantities of proto-peroxide for reduction ; but here another 

 difficulty arises, from the fact that the proto-peroxide is an ex- 

 ceedingly hygroscopic substance. And as manganese is usually 

 determined by converting the carbonate into proto-peroxide by 

 ignition, this property of the latter body may give rise to errors 

 if not specially guarded against. 



A determination was made by converting the protoxide into 

 proto-peroxide by igniting it in contact with atmospheric air. 

 It gave in two experiments the numbers 27*486 and 27*527, or 

 in mean 27*506, which confirms the one obtained from the ex- 

 periments with the sulphate. 



XXIV. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 150.] 



Jan. 14, 1858.— The Lord Wrottesley, President, in the Chair. 



THE following communications were read : — 

 " On the Electric-Conducting Power of the Metals." By Au- 

 gustus Matthiessen, Ph.D. 



The following values for the conducting power of the metals were 

 determined in the Physical Laboratory at Heidelberg, under the di- 

 rection of Professor Kirchhoff, by the same method as is described in 

 the 'Philosophical Magazine,' Feb. \Hf)7 . 



