MANGANIC AND PERMANGANIC ACIDS, and liThi0„ respectively. Two important acid compounds of manganese. The former is unknown in the free state, but is well known iu the form of certain of its salts, termed manganntla. The most important of these a re the manganates of potassium and barium Potassium manganate is ob tained by fusing manganese dioxide with eau-, tie potash and potassium chlorate; on cooling. the mass is dissolved iu a moderate quantity of water, and the solution is allowed to evaporate in vacuo. The salt thus obtained is unstable, being readily decomposed by acids, or even by an excess of water, into potassium permanganate (,..pe further below), caustic potash. and man ganese dioxide. It is this reaction that causes the well-known change of color in solutions of potassium inanganate. The manganate of barium is obtained by heating barium oxide with man ganese dioxide; it may be used as a green pig ment. Manganie anhydride, or manganese tri oxide (3Inti..). may he obtained by dissolving potassium permanganate in strong sulpuric acid and heating the solution.
Permanganic acid may he obtained in the uncombined state by the action of sulphuric acid on barium permanganate; but the resulting solu tion decomposes with extreme readiness and hence the acid cannot be isolated from it. The solu tion is deep-red in color and has powerful oxidiz ing and bleaching properties. The most impor tant among the permanganates, or salts of per manganie acid. is the permanganate of potas sium ( KM110,1, which forms long prismatic crystals having a deep-red color by transmitted light and a green metallic lustre. It may be pre pared by heating one of the oxides of manganese with an alkali and potassium ehlorate or some other oxidizing agent, and heating the resulting mass with water, when manganese dioxide is precipitated and potassium permanganate re mains in solution. A method of preparation often employed consists in adding potassium chlorate to a solution of caustic potash. adding finely powdered mineral manganese dioxide to the solution. evaporating to dryness, heating the residue to a selli-liquid condition, allowing to cool, dissolving the resulting mass in hot and passing into the solution a current of carbonic acid gas. until the transformation appears to be
complete. The solution is then filtered through guncotton, concentrated by evaporation, and al lowed to crystallize. In the solid state, as well as in. concentrated solutions. potassium perman ganate is very readily decomposed. Mixed with sulphur and phosphorus, solid potassium per manganate can he ignited hy striking. _Mixed with charcoal, it can lie ignited by moderate heat ing. its saturated solution (one part in 15 parts of water at ordinary temperature) decom poses on the application of gentle heat and even on standing for some time at ordinary tem peratures. Even in dilute solution potassium permanganate acts as a powerful oxidizing agent, and upon this are based many of its uses in medicine. analytical chemistry, and the arts. Sugar and many other organic substances are readily oxidized by it. Potassium iodide (in solution ) is converted by it into potassium iodate. If a solution of rotassium permanganate is mixed with one of peroxide of hydrogen (another oxidiz ing agent), the two substances give up part of their oxygen simultaneously. so that both are reduced at the same time. The oxidizing power of potassium permanganate is considerably in creased in the presence of acids. Among the uses of the permanganate may be mentioned its use for the preparation of oxygen, its use as a bleaching agent, its use in the purification of water, ammonia, and carbonic acid gas, its use in photography, and tinaily its use as a disin fectant, deodorant, and antiseptic in medicine. It is employed as a deodorant for bed-pans and as a wash for the hands, the solution commonly used being known as `Condy's red fluid.' In a very dilute form it may be used as a mouth wash or gargle and as an injection in eases of gonorthwal and other morbid discharges. Ac cording to sonic authors, if given internally in the form of pills, potassium permanganate has an action much like that of the salts of iron. The purinanganate of sodium is very similar to that of potassium. and is prepared by an analogous method. In the arts, sodium permanganate is often employed in place of the potassium salt, but the latter alone is employed in chemical analysis. Permanganie anhydride, or manga nese heptoxide, is extremely unstable.