PEROXIDE OF MANGANESE. 535 



ployed in the preparation of oxygen and chlorine. It generally 

 occurs massive, of an earthy appearance, and contaminated 

 with various substances such as peroxide of iron, silica and 

 carbonate of lime ; but sometimes of a fibrous texture, consist- 

 ing of small prisms, radiating from a common centre. Its den- 

 sity varies from 4.819 to 4.94 ; as a mineral species it has been 

 named pyrolusite* Another important variety of this ore, 

 known as wad, is essentially a hydrate, containing 1 eq. of 

 water to 2 eq. of peroxide, according to Dr. Turner. A hy- 

 drated peroxide, consisting of single equivalents of its consti- 

 tuents, is formed by precipitating the protosalts of manganese 

 by chloride of lime ; and the same compound results from the 

 decomposition of the acids of manganese, when diluted with 

 water or an acid. It is possible that the equivalent of this oxide 

 should be doubled, and that its proper formula is Mn 2 O 4 , 

 corresponding with peroxide of chlorine, Cl O 4 . 



The peroxide of manganese, loses one fourth of its oxygen at 

 a low red heat and is changed into deutoxide ; by the effect of a 

 bright red heat it loses more oxygen, and becomes red oxide, 

 the condition into which all the oxides of manganese pass when 

 ignited strongly in the open air. The peroxide does not unite 

 either with acids or with alkalies. When boiled with sulphuric 

 acid it yields oxygen gas and a sulphate of the protoxide. In 

 hydrochloric acid it dissolves with gentle digestion, evolving 

 chlorine gas, and forming protochloride of manganese, (page 

 357). It is extensively used in the arts for preparing chlorine, 

 and also to preserve glass colourless by its oxidating action. 

 In the last application, it is added to the vitreous materials in a 

 relatively small proportion, and becomes protoxide, which is not 

 a colouring oxide, while as deutoxide it would stain glass purple. 

 At the same time it destroys carbonaceous matter, and converts 

 protoxide of iron, which colours glass green, into peroxide 

 which is less injurious. 



The mineral varvicite was discovered by Mr. Phillips among 

 some ores of manganese from Hartshill in Warwickshire. It is 

 distinguished from the peroxide by being much harder, having 

 more of a lamellated structure, and by yielding water freely 

 when heated to redness. Its density is 4.531. It may be sup- 



* From Trvp, fire, and \v<, I wash, in allusion to its being employed to 

 discharge the brown and green tints of glass. 



