256 Dr. Turner's Remarks on Mr. Phillips's Essay. 



compounds is likewise indicated during the act of pulverizing 

 the mineral, some portions yielding readily to pressure, and 

 others giving considerable resistance. Manganite and the 

 peroxide are not mixed in any uniform proportion. The 

 harder, compact, laminated parts consist chiefly of manganite; 

 and the peroxide pi'evails in those portions which are made 

 up of small crystalline grains, so loosely cohering that they 

 crumble down under the pressure of the fingers. These por- 

 tions are very soft, and yield a black powder almost as dark 

 as pure peroxide, and which like it is disposed, when touched, 

 to soil the fingers. Their specific gravity is ^'S** ; whereas 

 the specific gravity of pure peroxide varies, according to my 

 observation, from 4*819 to 4*94. 



Tlie analysis of the Warwick ore confirms this view. The 

 ore indiscriminately reduced to powder, and exposed to a white 

 heat, loses, as you state, about 13*26 per cent, 5'4 parts of 

 which are water. The powder which collects when the ore is 

 broken into small fragments with a hammer, lost in a white 

 heat 13* 13 per cent, only 4*9 7 of which were water. The 

 water in the softest portions above described amounted to only 

 2*97 per cent. 



These observations, admitting their accuracy, fully justify 

 the conviction expressed at the commencement of this letter, 

 that the Warwickshire ore is not a definite compound of man- 

 ganese and oxygen, but a mixture, variable in different parts, 

 of manganite and peroxide. That you will find the remarks 

 accurate I do not entertain the least doubt ; for I would not 

 venture, without being very sure of my facts, to differ from 

 so experienced and expert a chemist. 



In order to facilitate your inquiry, I send several fragments 

 of the Warwick oi'e, some of which are nearly pure manganite, 

 others are soft and consist chiefly of the peroxide, and in others 

 both oxides occur together. For the sake of comparison I also 

 send some fragments of crystals of the Ihlefeld manganite. 



It is worthy of remark, that in the Warwickshire manganese 

 the manganite abounds most in the outer portions, while the 

 peroxide is most abundant in the interior. There is no ap- 

 pearance, therefore, of the ore having been originally manga- 

 nite, and subsequently converted, in part, into peroxide by a 

 process of disintegration. To justify that supposition, the re- 

 lative position of the two oxides ought to be precisely the re- 

 verse. 



II. I now^ proceed to show that the doubt which you ex- 

 press concerning the accuracy of my analysis of manganite, is 

 without foundation. You appear to imagine that the quantity 

 of water reported in my analyses, was inferred from the loss 



which 



