nary atmospheric humidity, but they do so slowly in warm, dry air. When heated, they lose their water of crystallization without previously undergoing aqueous fusion, and at a red heat undergo igneous fusion, with partial decomposition. FIG. 136. Magnesium sulphate is soluble in 0.8 part of water at 15° C. (59° F.), and in 0.15 part of boiling water, but is insoluble in alcohol; its aqueous solution has a nauseous, bitter taste, and is neutral in its action upon litmus; it is decomposed, and gives white precipitates, with the fixed alkaline hydrates and carbonates, and also with the earthy hydrates and their soluble salts; ammonia-water and ammonium carbonate, however, do not at once cause a precipitate in dilute solutions of magnesium sulphate, or, if so, but a very slight one, since ammonium salts when present, or when formed by the neutralization of acidulous solutions, act as a solvent for magnesium hydrate or carbonate, and thereby retard or prevent their precipitation; but, on the subsequent addition of phosphoric acid or solutions of tri-basic phosphates, a complete precipitation takes place, which precipitate, however, is soluble in dilute acids. The crystals of magnesium sulphate are isomorphous with those of zinc sulphate, and cannot be distinguished from them by the eye; it is easy, however, to discriminate between them, not only by the difference in taste, but also by the action of a few drops of ammonium sulphide or solution of potassium ferrocyanide on their aqueous solutions; that of magnesium sulphate remains unaffected by these reagents, whereas solution of zinc sulphate yields, in either instance, a white precipitate. Examination : Metallic impurities may be detected in the solution of the salt, acidulated with hydrochloric acid, by the occurrence of a turbidity or precipitate upon saturation with hydrogen sulphide (an ensuing white turbidity may be due simply to sulphur, a lemon-yellow one will indicate arsenic), and, after filtration, if necessary, and neutralization with ammonia-water, by the subsequent addition of ammonium sulphide; a white precipitate with the latter reagent would ind cate zinc; when a dark precipitate is formed, both with the hydrogen sulphide and ammonium sulphide, cop per and iron are indicated, and may be confirmed in the slightly acidulated solution of the salt, the former by a reddish-brown precipitate, the latter by a blue one, with potassium ferrocyanide. Alkaline sulphates may be detected by triturating 2 parts of the magnesium sulphate with an equal weight of dry calcium hydrate (from which any free alkali must have been previously removed by washing with water, and again drying), and adding this mix ture to a mixture of 10 parts of alcohol and 10 parts of water. The mixture is then allowed to stand for about two hours, with frequent agitation, when 40 parts of absolute alcohol are added, and, after active agitation, the mixture poured upon a filter which has been previously moistened with alcohol. If an alkaline sulphate be present in the magnesium sulphate, it will be contained in the alcoholic filtrate in the form of hydrate, and may then readily be detected by its action upon turmeric paper; if litmus paper be employed, the alcoholic liquid should be mixed with a little water, and the alcohol dissipated by the aid of heat before the application of the test. Ammonium salts may be detected by the odor of ammonia, when a little of the salt is heated, in a test-tube, with a strong solution of potassium hydrate, or by the development of white fumes when a glass rod, moistened with acetic acid, is held over the orifice of the tube. Aluminium and Calcium Salts.-The former may be detected in the solution of magnesium sulphate, to which a sufficient amount of ammonium chloride has been added, by the formation of a colorless, flocculent precipitate on the addition of ammonia water; and the latter by a white precipitate on the addition of ammonium oxalate. Chlorides may be detected in the diluted solution of the salt, acidulated with nitric acid, by a white turbidity on the addition of solution of argentic nitrate. Estimation: One hundred parts of magnesium sulphate, dissolved in boiling water, and completely precipitated by a boiling solution of sodium carbonate, yield a precipitate which, when washed, dried, and ignited at a red heat, weighs 16.26 parts. The quantitative estimation of magnesium in magnesium sulphate is, however, usually effected by its precipitation as ammoniomagnesium phosphate, and the conversion of the latter, by ignition, into magnesium pyrophosphate; from the weight of the latter, the amount of magnesium oxide, or the corresponding amount of crystallized magnesium sulphate may readily be calculated. To the aqueous solution of a weighed amount of the salt, ammonium chloride and ammonia-water are added, and subsequently solution of sodium phosphate until no further precipitate is produced; the mixture is allowed to stand for ten or twelve hours, when the precipitate is collected upon a filter, washed with a mixture of about one part of ammonia-water and three parts of water, and, when dry, completely incinerated in a porcelain crucible. Of the residue of magnesium pyrophosphate, Mg,P,O,, thus obtained, 100 parts correspond to 36.03 parts of magnesium oxide, MgO, or 221.62 parts of crystallized magnesium sulphate, MgSO, +7H2O. MAGNESII SULPHIS. MAGNESIUM SULFUROSUM. Sulphite of Magnesium. Magnesium Sulphite. Ger. Schwefligsaures Magnesium; Fr. Sulfite de magnésie; MgSO,+6H,0; 212. A white, crystalline powder, containing 6 molecules (50.94 per cent.) of water of crystallization; it is odorless, but possesses a slightly bitter, somewhat sulphurous, taste, and a neutral or slightly alkaline reaction; on exposure to the air, it gradually absorbs oxygen, and becomes converted into magnesium sulphate. When heated to 200° C. (392° F.), the salt loses its water of crys tallization, and becomes decomposed, being converted into magnesium oxide and anhydrous magnesium sulphate. Magnesium sulphite is soluble in 20 parts of water at 15° C. (59° F.), and in 19 parts of boiling water; it is insoluble in alcohol. The aqueous solution, when mixed with solution of ammonium chloride and ammonia-water, yields. upon the subsequent addition of solution of sodium phosphate, a white crystalline precipitate, which is insoluble in water or dilute ammonia-water, but readily soluble in acids. Magnesium sulphite is also completely soluble in 4 times its weight of dilute hydrochloric acid, with the development of the odor of burning sulphur, but without producing any turbidity (distinction from magnesium hyposulphite). A 1 per cent. aqueous solution of the salt, strongly acidulated with hydrochlorie acid, should not afford more than a slight cloudiness on the addition of solution of barium chloride (absence of and distinction from magnesium sulphate). MANGANI OXIDUM NIGRUM. MANGANUM HYPEROXYDATUM. MANGANESIUM OXYDATUM NATIVUM. Black Oxide of Manganese. Pyrolusite. Manganese Dioxide. Heavy, compact masses, of a dull-black or brownish-black, earthy appearance, or masses of acicular or rhombic crystals of a black, metallic lustre, and, if pure pyrolusite, of a spec. grav. of 4.9. In commerce, it occurs usually ground, as a coarse, dull, black powder, consisting of manganese dioxide, sesqui-oxide, aud monoxide, and is contaminated with the gangue (quartz, felspar, barytes, limestone, etc.), which frequently amounts to 40 or 50 per cent. 3 Manganese dioxide is infusible, permanent in the air, and insoluble in water or alcohol. When exposed to a strong red heat, it loses one-third of its oxygen, and is converted into reddishbrown mangano-manganic oxide, Mn,O,: 3MnO, = Mu ̧0 ̧+0 ̧. It is not attacked by cold concentrated sulphuric acid, but, upon heating with the latter, it is converted into manganous sulphate, with the evolution of oxygen: MnO2+H2SO ̧ = MnSO ̧+ H2O+0. 2 If, however, oxalic acid, or other readily oxidizable organic substances are present, manganese dioxide is also dissolved by dilute sulphuric acid, with the evolution of carbon dioxide: When heated with hydrochloric acid, it is converted into manganous chloride, with the development of chlorine: MnO2 + 4HCl = MnCl2 + 2H2O + Cl2. The resulting brownish solution, when filtered and neutralized with ammonia-water, yields, with hydrogen sulphide or ammo. nium sulphide, a flesh-colored precipitate of manganous sulphide; the color of this precipitate is, however, frequently rendered darker, or even brownish-black, by the presence of oxides of iron and other metals. When a small portion of manganese dioxide is mixed with about an equal weight of potassium hydrate and a little potassium nitrate or chlorate, and the mixture heated to redness upon platinum-foil, it yields a dark green mass, which dissolves in water with a green color, changing to purple when the solution is boiled or on the addition of dilute sulphuric acid. Examination: As manganese dioxide is frequently employed in connection with potassium chlorate for the generation of oxygen gas, its perfect freedom from organic contaminations should be conclusively established, as the latter may give rise to violent and dangerous explosions. The presence of organic impurities in general may be determined by strongly heating a little of the powdered manganese dioxide in a glass tube, when no combustion should take place, nor should carbonic acid gas be evolved. Black antimonious sulphide, which, by accident or through carelessness, may become mixed with or substituted for manganese dioxide, may be readily detected by the development of the odor of hydrogen sulphide in contact with dilute hydrochloric acid, and, after boiling with the latter, and filtering, by the production of an orange-colored precipitate upon saturation with hydrogen sulphide. Since, however, the value of commercial black oxide of manganese or pyrolusite, for most of its applications in the arts and trades, depends less upon the nature of its impurities than upon the percentage of real manganese dioxide, an examination of the mineral is invariably required before its application, and is mainly directed to the determination of the amount of dioxide. FIG. 137. Among the several methods of conducting the assay, the two following are simple and accurate, the one being an approximate, the other a quantitative one: I. Five grams of the finely powdered black oxide of manganese are added, in a small flask (Fig. 137), to a solution of 21 grams of crystallized or granular ferrous sulphate in 15 grams of water and 45 grams of hy. drochloric acid, and, when mixed by gentle agitation, the whole is heated for a few minutes to boiling; after being allowed to cool, the liquid is filtered, and the filtrate subsequently tested with potassium ferricyanide; if it gives no blue precipitate, the test bears evidence that the pyrolusite contains at least 66 per cent. of real manganese dioxide; if a blue precipitate is produced, the peroxide is wanting in that strength in proportion to the amount of the precipitate. II. Three grams of the black oxide of manganese, in fine pow der, and previously dried at about 120° C. (248° F.), are care FIG. 138. fully introduced into the flask K' (Fig. 138) of the little apparatus described on page 86, into which previously has been poured sufficient of a mixture of 1 part of concentrated sulphuric acid and 2 parts of water to fill the flask to about one-third of its capacity. The apparatus is then brought upon the balance, and, together with from 8 to 9 grams of pure crystallized oxalic acid, is accurately weighed. The oxalic acid is then added to the mixture, being careful to avoid any loss, the cork carrying the tubes is adjusted, and the ensuing reaction effected by gentle agitation; the flask K is charged with a little concentrated sulphuric acid, through which the evolved carbonic acid gas has to pass, and which absorbs and retains the moisture; gentle heat is applied to the flask K', as long as a brisk evolution of gas takes place; the process is completed when this action and |