172 Dr TURNER'S Chemical Examination 



When heated to redness Psilomelane gives out 6*216 per 

 cent of water. The diminution in weight occasioned by expo- 

 sure to a white heat is 13*58 per cent ; and on subtracting 6*216 

 for water, there remains 7*364 as the loss in oxygen. 



To ascertain the quantity of baryta 30*028 grains of the mi- 

 neral were dissolved in muriatic acid, and the baryta precipitated 

 by means of the sulphate of soda, a considerable excess of mu- 

 riatic acid being allowed to remain in the liquid, to prevent any 

 manganese from adhering to the precipitate. The sulphate of 

 baryta, after exposure to a red heat, amounted to 7*434 grains, 

 equivalent, according to the atomic numbers of Dr THOMSON, to 

 4*914 grains, or 16*365 per cent of pure baryta. 



According to this analysis, 100 parts of Psilomelane have 

 yielded of 



Red oxide 69795 



Oxygen 7'364 



Baryta 16*365 



Silica .:..*.. 0*260 



Water 6*216 



100*000 



The precise atomic constitution of Psilomelane is not made 

 apparent by this analysis ; and, indeed, the result is of such a 

 nature as to leave no doubt of this mineral containing more 

 than one oxide of manganese. For it follows, from the quantity 

 of oxygen expelled by heat, that a considerable part of the man- 

 ganese must be in the form of peroxide ; but it is equally clear 

 that the whole of it cannot be in that state, because 69*795 parts 

 of red oxide require 9*627 instead of 7' 364 parts of oxygen to 

 constitute the peroxide. On perceiving this deficiency of oxy- 

 gen, I at first suspected that the baryta might prevent the usual 



