418 Contribulions to ike [June, 



a portion of its oxygen, became greenish grey ; and the black 

 oxide in like manner became white : but it is not possible to deter- 

 mine ihe dillerence in the quantity of oxygen which these supposed 

 oxides contain. 



JNlanganese is so much inclined to form red solutions in acids, 

 that one might be disposed to suspect that one of its oxides has a 

 red colour; but I have not only not been able to establish the ex- 

 istence of any such oxide, but not even able to obtain any red pre- 

 cipitate from such solutions. Hence I consider the statement con- 

 tained in diflerent chemical systems of the existence of this red 

 oxide as erroneous. 1 am not ignorant that nature presents to us 

 red coloured minerals, which if we trust the analyses that have 

 been made of them, owe their red colo)ir to manganese ; for 

 example, milk quartz and Siberian red schorl. But it is well 

 known, tliat when various substances are united together, they 

 modify tlie colour of each other. It is equally well known, that 

 nothing is easier in such analyses, than to overlook the real colour- 

 ing matter altogether. Hence 1 do not consider the existence of 

 these minerals as a proof that manganese is capable of forming a 

 red oxide. 



A. Examination of the green Oxide. 



a. Oxidation of Manganese by ihe Decom/josition of Water. 



Metalh'c manganese decomposes water at the ordinary tempe- 

 rature of the atmosphere with considerable rapidity. The metal is 

 changed into a greyish green oxide, combining with the oxygen of 

 the water, while the hydrogen makes its escape. I put 80 grains 

 of pure metal into a small vessel, contrived so as to collect the gas, 

 and filled the vessel with distilled water. The gas occupied very 

 nearly the bulk of 24 ounces of water. It was hydrogen gas, but 

 probably held in solution some atoms of the metal; for it liad a 

 peculiar smell, and Ijurnt with a green coloured flame. The evo- 

 lution of the gas continued for a whole day and then stopped ; and 

 though the water was heated, the oxide did not appear to undergo 

 any change. It was rapidly dried in "a close vessel, and was found 

 to weigh 92 grains. Hence green oxide of manganese is a com- 

 pound of 



Metal 8C-97 



Oxygen 13-03 



100-00 



Wlien this oxide comes in contact with the air, cither imme- 

 diately or tlirough water, it absorbs more oxygen, and is changed 

 into brown oxide. 



I. Estimation of the Proportion of Oxygen^ the drij luaij. 



It has been formerly sliown that, in order to form 100 jjarts of 

 carbonate of manganese, 48-60 parts of the metal are required, 



