For technical purposes it is also prepared by melting solid potasssium hydrate with finely-powdered manganese dioxide, with or without the addition of potassium nitrate.

The crystals of this substance are isomorphous with those of potassium sulphate. They dissolve in water to give a dark-green color. When allowed to stand, the color of this solution gradually passes through blue and violet into red, on account of the formation of potassium permanganate. This change is hastened by heat and by the action of carbon dioxide, nitric acid, chlorine, and bromine.

Because of these changes in color the early chemists called the salt chameleon mineral, although the same name has also been applied to the permanganate.

Organic substances, sulphur dioxide, and other reducing bodies decolorize a solution of potassium manganate by taking up its oxygen. For this reason its solutions cannot be filtered through paper.

By substituting the corresponding sodium compounds in relative proportion, green crystallized sodium manganate, Na,MnO4+10H2O, can be obtained by the method employed for the potassium salt.

Barium Manganate, BaMnO4, is easily produced by roasting. a mixture of 1 part of powdered manganese dioxide with 4 parts of barium nitrate, and rapidly lixiviating the green mass. It is an emerald-green, crystalline, insoluble powder, sometimes called barium green.

Potassium Permanganate, K.MnOg Potassii Permanganas, U. S. P.—To prepare this salt the green, fused mass obtained in making potassium manganate is treated with twice its weight of hot water. After stirring, the mixture is allowed to settle, and the clear, green solution produced is poured off. The sediment is washed with more water by affusion and decantation after subsidence. The mixed clear solutions are warmed in a water-bath, at which temperature a current of carbon dioxide is conducted into the liquid until a pure red-violet color has been acquired:

3KMnO2CO2 = KMnO + MnO2 + 2K¿CO§.

The manganate can also be converted into permanganate by thoroughly boiling the solution, potassium hydrate resulting as one of the products of the change:

3KMnO4 + 2H2O

=

K2Mn2O + MnO2 + 4KOH.

In both cases a precipitate of hydrated dioxide is produced. After standing, the clear solution is siphoned off, and the last turbid portion is filtered through asbestos. Care having been taken to exclude dust, the liquid is evaporated until a pellicle forms on the surface, and then allowed to cool. The crystals which separate are collected and placed to drain out of contact with organic matter. The salt may be obtained in a crude state by evaporating the solution at once to dryness. It forms metallic, lustrous, almost black, rhombic prisms, which are permanent in the air. These are soluble in 16 parts of water at 15°, and in 3 parts of boiling water. The solution gradually undergoes change. Potassium permanganate is a powerful oxidizing agent toward organic and inorganic substances. In neutral solution one molecule of the salt gives up three atoms of oxygen, with the production of a brown, flocculent precipitate of a hydrated dioxide.

In acid solution one molecule gives up five atoms, and if sufficient of the oxidizable matter is present, a clear and colorless solution results. On account of the ease with which they yield their oxygen, both manganate and permanganate are employed as disinfectants: foul-smelling gases or substances are rendered entirely odorless by contact with these compounds. Its use in the quantitative analysis of iron and of organic matter in potable waters depends upon this same feature. Chlorine is liberated by the action of hydrochloric acid on potassium permanganate. The salt is occasionally used in the practice of medicine.

Sodium Permanganate, Na,Mn,О.6H2O, is prepared by a method similar to that used for making the potassium salt. It is a very hygroscopic, and therefore difficultly crystallizable, substance.

Ammonium Permanganate, (NH),MnO, is isomorphous with the potassium compound. It results upon the double decomposition of molecular quantities of barium permanganate and ammonium sulphate, or of silver permanganate and ammonium chloride. It is easily decomposed by heat.

Barium Permanganate, BaMnOg, forms needle-shaped, almost black crystals, and is gotten by the action of carbon dioxide on barium manganate suspended in water, or by reacting on silver permanganate with barium chloride.

Zinc Permanganate, ZnMn,Og, as easily-decomposable, deep dark-red, lustrous crystals, is prepared by decomposition of barium permanganate by the proper amount of zinc sulphate, or of silver permanganate by zinc chloride, and evaporation of the supernatant liquid in vacuo.

Permanganic Acid, H,MnO, is known only in aqueous solution. It may be made by the action of dilute sulphuric acid on barium permanganate, or by boiling a manganese compound that is free from chlorine with nitric acid in the presence of red oxide of lead. The production of its rose-red color by the last method is used as a test for manganese under the name of Crum's process.

Permanganic Anhydride, MnO,, is the oxide which corresponds to permanganic acid. As a heavy, greenish-black, readily decomposing liquid, it is produced when potassium permanganate is added in small quantity to well-cooled concentrated sulphuric acid.

The greatest care should be exercised in the application of these substances as oxidizing agents, as explosion is likely to occur if the action is sudden.

MANGANESE AND SULPHUR.

Two sulphides of manganese are found native. Manganese monosulphide, MnS, occurs as manganese-blende in black, cubic crystals, and manganese disulphide, MnS,, as hauerite in redbrown crystals of the same system.

The former sulphide may be prepared as a green powder by heating manganese sesquioxide in a stream of hydrogen sulphide, or by precipitating a solution of a manganous salt with an alkali sulphide, whereby a flesh-pink precipitate of a hydrated sulphide is thrown down. Upon exposure to air, this takes up oxygen and assumes a brown color.

OXYGEN SALTS OF MANGANESE.

Manganous Sulphate, MnSO4.4H2O. Mangani Sulphas, U. S. P. This salt is prepared by rubbing a convenient quantity of finely-powdered dioxide of good quality to a thick paste with concentrated sulphuric acid, then heating the mixture in a Hessian crucible by a blast-furnace gradually to low redness, and maintaining that condition as long as white fumes of sulphur trioxide are evolved:

MnO2 + H2SO4

=

MnSO4 + H2O + 0.

From time to time a portion of the mass is taken out, allowed to cool, and treated with water. The solution is then filtered and tested for iron, which, if found, necessitates heating the materials to full redness, until after another trial the water solution is found to be destitute, or nearly so, of iron.

The gray-white mass is allowed to cool, and is then powdered and extracted with three times its weight of hot water, which, by frequent stirring, dissolves the salt.

Most, if not all, of the iron is left undissolved as oxide. Any traces remaining in solution are removed by manganous carbonate, which precipitates the impurity as hydrate. The filtered, iron-free solution is slowly evaporated at a low temperature.

Lead and copper are removed by saturating the liquid with hydrogen sulphide previous to evaporation, while zinc is separated by the same reagent, but in the presence of sodium acetate and acetic acid.

Manganese sulphate forms pale, rose-colored crystals which are somewhat efflorescent, and the amount of whose water of crystallization and whose crystalline form vary according to the temperature at which the crystals separate. Besides that of official composition which contains four molecules of water of crystallization, and which is obtained in rhombic prisms between 20° and 30°, monoclinic crystals having the formula MnSO,.7H2O can be produced below 6°. They are isomorphous with ferrous sulphate. Between 7° and 20° a salt of the composition MnSO4.5H2O crystallizes in the triclinic system, which also includes copper sulphate. When the solution is evaporated at a temperature above 30°, an almost colorless, difficultly soluble, crystalline powder of still lower percentage of water separates.

The official salt is soluble in an equal weight of water to produce a neutral solution. It is not soluble in alcohol. With the sulphates of potassium and sodium, manganese sulphate gives crystalline monoclinic double salts. Manganous sulphate finds a limited use in medicine.

Manganic Sulphate, Mn(SO)„, is a dark-green, deliquescent powder which results from the action of concentrated sulphuric acid on manganese sesquioxide or on the dioxide at from 100° to 140°.

Manganese alums crystallize in octohedra, and arise from the union of the alkali sulphates with manganic sulphate.

Manganous Nitrate, Mn(NO3)2.6H2O, separates in deliquescent crystals when manganese carbonate is added to nitric acid and the solution is evaporated.

Manganous Phosphate, Mn,(PO4)2.7H2O, is produced as a white precipitate by the addition of sodium phosphate to a solution of manganous sulphate.

Manganese Borate is formed when a solution of a manganous

salt is precipitated by sodium borate. The white precipitate thrown down becomes brownish upon drying.

Manganous Carbonate, MnCO,.-Manganese-spar, the native form of this compound, occurs in red, hexagonal crystals, which are contaminated with iron and other carbonates. The artificial white salt is prepared by adding a slight excess of sodium carbonate to a solution of manganous sulphate. Upon drying it undergoes some decomposition and becomes darker on account of the sesquioxide formed. When ignited it loses carbon dioxide and leaves manganoso-manganic oxide.

Manganic Phosphate, Mn,(PO4)2.2H2O, consists of a greenish-gray powder, which is obtained by the gradual addition of a concentrated solution of manganous nitrate to a 25 per cent. solution of phosphoric acid previously heated to and subsequently maintained at 100°. Dilute nitric or sulphuric acid does not alter it, but concentrated hydrochloric acid dissolves it, chlorine being set free.

Manganic Arsenate, Mn,(AsO4)2.2H2O, can be prepared in the same manner as is the manganic phosphate. It is a gray powder.

MOLYBDENUM, TUNGSTEN, URANIUM.

In addition to chromium and manganese, in the foregoing group we have the rarer elements molybdenum, tungsten, and uranium.

The whole group possesses many points of resemblance to the sulphur group of non-metals. The members have an equivalence II, IV, VI, and some of them more rarely VIII.

Molybdenum, Mo. Atomic Weight, 95.9.—This element occurs in nature chiefly as molybdenite, MoS, and as wulfenite, a lead molybdate, PbMoO4. It is more rarely found as the trioxide, MoO.

Molybdenum is prepared by heating the chloride or oxide to a high temperature in a current of hydrogen. It is a silver-white, infusible metal, harder than topaz, and having a specific gravity of 8.6. It is permanent in the air, unless heated, when it is slowly converted into the trioxide. Hydrochloric, hydrofluoric, and dilute sulphuric acids do not dissolve it, but it is readily attacked by nitric acid and nitro-hydrochloric acid.

Molybdenum Pentachloride, MoCl5, is formed by gently heating the metal in a current of chlorine. The trichloride is prepared from this by heating to 250° in a current of hydrogen. The dichloride and tetrachloride are also known.

Molybdenum Trioxide, MoO,, is the final product of the oxidation of the metal. The other oxides are prepared from this by various processes of reduction. They are MoO2, Mo2O3, and MoO.

Molybdic Acid is a term applied to the trioxide, and its combinations with various bases are known as molybdates.