Manganic Acid. H2MnO4. This acid has not yet been obtained free, but some of its salts are extensively employed as disinfectants, as “green Condy’s fluid.” The chief compounds are the following:—
Manganic Hydrate. Mn2(HO)6. Syn. Hydrated sesquioxide of manganese. Found native as “manganite,” in reddish-brown crystals. Prep. By passing a current of air through recently precipitated and moist
manganous hydrate. Soft dark brown powder converted into the oxide by heat.
Manganic Oxide. Mn2O3. Syn. Sesquioxide of manganese. Found native as “Braumite,” and readily formed by exposing manganous hydrate to the action of air, and drying, or by gently igniting the peroxide brown or black powder decomposed by heat.
Manganic Peroxide. MnO2. Syn. Permanganic oxide, Binoxide of manganese, Peroxide of manganese, Black oxide of manganese, Oxide of manganese, Manganesii oxidum nigrum (B. P.), Manganesii binoxydum (Ph. L.), Manganese oxydum (Ph. E.).
It is the only oxide of manganese that is directly employed in the arts. It is a very plentiful mineral production, and is found in great abundance in some parts of the West of England. The manganese of the shop is prepared by washing, to remove the earthy matter, and grinding in mills. The blackest samples are esteemed the best. It is chiefly used to supply oxygen gas, and in the manufacture of glass and chlorine; in dyeing and to form the salts of manganese. It has been occasionally employed in medicine, chiefly externally in itch and porrigo, made into an ointment with lard. It has been highly recommended by Dr Erigeler in scrofula. Others have employed it as an alterative and tonic with variable success. When slowly introduced into the system during a lengthened period, it is said to produce paralysis of the motor nerves. (Dr Coupar.)—Dose, 3 to 12 gr., or more, thrice daily, made into pills.
Pur. Native binoxide of manganese (pyrolusite) is usually contaminated with variable proportions of argillaceous matter, calcium carbonate, ferric oxide, silica, and barium sulphate, all of which lower its value as a source of oxygen, and for the preparation of chlorine. The richness of this ore can, therefore, be only determined by an assay for its principal ingredient.
Assay. There are several methods adopted for this purpose, among which the following recommend themselves as being the most accurate and convenient.
1. A portion of the mineral being reduced to very fine powder, 50 gr. of it are put into the little apparatus employed for the analysis of carbonates described at page 406, together with about 1⁄2 fl. oz. of cold water, and 100 gr. of strong hydrochloric acid, the latter contained in the little tube (b); 50 gr. of crystallised oxalic acid are then added, the cork carrying the chloride of calcium tube fitted in, and the whole quickly and accurately weighed or counterpoised; the apparatus is next inclined so that the acid contained in the small tube may be mixed with the other contents of the flask, and the reaction of the ingredients is promoted by the application of a gentle heat; the disengaged chlorine resulting from the mutual decomposition of the hydrochloric acid
and the manganic peroxide converts the oxalic acid into carbonic acid gas, which is dried in its passage through the chloride of calcium tube before it escapes into the air. As soon as the reaction is complete, and the residual gas has been driven off by a momentary ebullition, the apparatus is allowed to cool, when it is again carefully and accurately weighed. The loss of weight in grains, if doubled, at once indicates the percentage richness of the mineral examined in manganic peroxide; or, more correctly, every grain of carbonic anhydride evolved represents 1·982 gr. of the peroxide.