ally dissolves in water with a reddish-brown color. The solution is official as Liquor Ferri Tersulphatis, U. S. P. Ferric sulphate unites with alkali sulphates to form iron alums. Of these, the ammonium alum, Fe,(SO,),(NH4)2SO4.24H,O, is official as Ferri et Ammonii Sulphas, U. S. P. It crystallizes in "pale violet, octohedral crystals, without odor, and having an acid, styptic taste; efflorescent on exposure to the air." It is soluble in water, insoluble in alcohol.

A basic or subsulphate of iron is also official in solution as Liquor Ferri Subsulphatis, U. S. P., known commonly as Monsel's Solution. In its preparation, the ferrous sulphate taken is converted into ferric sulphate at the expense of the nitric acid added; but the sulphuric acid mixed with the nitric is in quantity insufficient to form the normal salt. The formula assigned to the salt contained in this solution is Fe‚O(SO), or according to other authorities Fe2(SO4) ̧5F¤ ̧ ̧. H2O.

Ferric Nitrate, Fe,(NO), is formed when iron is dissolved in nitric acid. It crystallizes either with 12 molecules of water in cubes or with 18 molecules in monoclinic crystals, both forms being colorless and deliquescent. A solution of the ferric nitrate is official as Liquor Ferri Nitratis, U. S. P.

Ferrous Phosphate, Fe3(PO4)2.8H2O, occurs as the mineral vivianite in bluish monoclinic prisms. Obtained artificially it is a white, amorphous powder, which speedily oxidizes in the air.

Ferric Phosphate, Fe2(PO4)2, is obtained as a white precipitate on adding sodium phosphate to ferric solutions. It is present in the official scale preparation Ferri Phosphas Solubilis, U. S. P.

Ferric Pyrophosphate, Fе4(P2O7)3, is the salt present in Ferri Pyrophosphas Solubilis, U. S. P., another scale preparation.

Ferric Hypophosphite, Feg(PH2O2), Ferri Hypophosphis, U. S. P., forms "a white or grayish-white powder, odorless and nearly tasteless; permanent in the air." Like other hypophosphites it is readily oxidized by oxidizing agents.

Ferrous Carbonate, FeCO,, occurs in nature as the mineral siderite or spathic iron. It is artificially obtained by adding sodium carbonate to ferrous solutions, forming a white precipitate which rapidly oxidizes in the air to ferric hydrate. The official preparation Ferri Carbonas Saccharatus, U. S. P., protects the carbonate by admixture with sugar. Ferrous carbonate is slightly soluble in water containing dissolved carbon dioxide, and hence is present in the natural chalybeate mineral waters.

Potassium Ferrocyanide and Ferricyanide are described later under the cyanogen compounds in Part IV.

The organic salts of iron, such as the Tartrate and Citrate, etc., are also noted in Part IV.

IRON AND SULPHUR.

Ferrous Sulphide, FeS, is obtained artificially by fusing together iron and sulphur. It forms a dark-gray or black metallic mass, which finds extended use in the chemical laboratory as a source of hydrogen sulphide gas. If flowers of sulphur and finely-divided iron are intimately mixed and then moistened with water, the union takes place at ordinary temperatures. Ferrous sulphide is also precipitated as a black precipitate by the use of alkali sulphides, in ferrous solutions directly and in ferric solutions after previous reduction of the iron salt to the ferrous state. Ferric Sulphide, FeS2, occurs abundantly in nature as pyrites, a mineral used on a large scale in the manufacture of sulphuric acid and green vitriol.

NICKEL.

Symbol, Ni. Atomic Weight, 58.6. Valence, II, (Ni2) VI and VI. History. The ore known as copper-nickel (niccolite) was known as early as 1694 to resemble copper in appearance without containing that metal, but it was only in 1751 that Cronstedt stated that it contained a foreign element to which, in 1754, he proposed to give the name of nickel.

Occurrence. The most important sources of nickel at present are the mines of New Caledonia, an island in the South Pacific belonging to France, and Sudbury, Ontario; the most important mine in the United States, that of Lancaster Gap, Pennsylvania, is now nearly exhausted. The ore worked in New Caledonia is the hydrated silicate of nickel and magnesia known as garnierite (or genthite), while that of Canada and Lancaster Gap is a nickeliferous pyrrhotite (magnetic pyrites). The sulphide known as millerite, and the arsenide (niccolite or copper-nickel), are also well-known ores. The nickel ores, especially the sulphide and arsenide, are always associated with the corresponding cobalt ores. The production of nickel throughout the world in 1893 was as follows:

Most of the Canadian ore, however, is smelted and reduced to metal in the United States.

Preparation and Properties.-Such nickel ores as contain sulphur or arsenic are first roasted, and the product, known as "speiss," is then dissolved in hydrochloric acid, and the separation of nickel from the accompanying metals accomplished in the wet way. The New Caledonian ore, being free from arsenic, sulphur, and cobalt, is smelted in a blast-furnace very much like iron ores, or it may be at once treated with hydrochloric acid, and the solution of nickel salt then precipitated with oxalic acid and the oxalate reduced to metal with lime and carbon.

Nickel is a lustrous white metal with a steel-gray tinge. Its specific gravity is 8.9. When pure it is malleable, and can be welded. The cast-nickel formerly obtained from arsenide and sulphide ores did not possess these properties, owing to the combined carbon, which made it like cast-iron. In 1879, Fleitmann discovered that the addition of % of 1 per cent. of magnesium rendered the nickel malleable and more fusible. Since then it has been found that manganese in amount from 2 to 5 per cent. would accomplish the same result. The purest nickel has been made by Mond, who takes up the metal in a gaseous compound by passing carbon monoxide over it at a moderate heat, and then at a higher temperature decomposes the compound, separating pure metallic nickel.

Uses of the Metal.-Nickel has long been used in admixture with copper and zinc in the manufacture of German silver; it has also been used with copper alone in coinage alloys, and within the last few years in the manufacture of nickel-steel armorplate, which has produced a great increase in the demand for the metal. Nickel-plating has also been an important utilization of the metal, as the coating, if well deposited, undergoes scarcely any oxidation, and takes a high polish. The solution from which the plating is done is always that of the nickel-ammonium sulphate.

Nickel Compounds.-Nickel, like iron, forms two well-defined series of salts the nickelous compounds, in which it has the valence two, and the nickelic, in which the double atom Ni, acts as a hexad group. The former series appear to be the more stable.

Nickelous Chloride, NiCl2.6H2O, forms green monoclinic prisms, soluble in water and alcohol. When heated they lose water, and when anhydrous show a yellow color.

Nickelous Cyanide, Ni(CN)2, is an apple-green precipitate easily soluble in excess of potassium cyanide, with the formation of a crystalline

double salt, Ni(CN)2.2KCN. This salt is easily decomposed by dilute acids, and therefore is not analogous to the ferrocyanides and cobalticyanides.

Nickelous Oxide, NiO, occurs sparingly in nature as the mineral bunsenite, and may be obtained artificially by igniting the hydrate, carbonate, or nitrate. It forms a green, crystalline powder.

Nickelous Hydrate, Ni(OH)2, is thrown down, when alkalies are added to nickelous solutions, as a bright-green precipitate. It dissolves in am. monia water with a blue color, and separates out as a green, crystalline powder on boiling the ammoniacal solution.

Nickelous Sulphate, NiSO4.7H2O.-This salt crystallizes from aqueous solutions in green, rhombic crystals, isomorphous with magnesium sulphate. From solutions containing an excess of acid there separate at ordinary temperatures NiSO4.6H2O, in bluish-green, quadratic pyramids, and at 50°-70° green, monoclinic crystals of the same composition. The double sulphate used for nickel-plating is NiSO4, (NH4)2SO4.6H2O. Nickelous Sulphide, NiS.—The sulphide is found in nature as millerite, of brass-yellow color. Obtained by precipitation by alkali sulphides in nickelous solutions it is black.

Nickelic Oxide, Ni2O, is a black powder obtained by gentle ignition of the nitrate or carbonate in air. It behaves like a peroxide, as it dissolves in sulphuric or nitric acid with evolution of oxygen, and in hydrochloric acid with evolution of chlorine.

Nickelic Hydrate, Nig(OH).—If chlorine be passed through the nickelous hydrate suspended in water, this higher compound is obtained. It is also formed as a black precipitate when the solution of a nickelous salt is warmed with an alkaline hypochlorite.

COBALT.

Symbol, Co. Atomic Weight, 58.6. Valence, II, (Co2)VI and VI. History. Certain ores containing cobalt were known to impart a blue color to glass when smelted with it, and in these Brandt, in 1735, pointed out the presence of a peculiar metal to which he gave the name of kobalt-rex. Thus the discovery of cobalt as a distinct element antedates that of nickel.

Occurrence.-Cobalt is found as sulphide (linnæite), and as mixed arsenide and sulpharsenide with nickel (speiss-cobalt and cobalt-glance), and arsenate (cobalt-bloom). The New Caledonian mines also afford an ore containing some 3 per cent. of cobaltic oxide, which is smelted by the Maletra Works at Rouen, France. Preparation and Properties of the Metal.-The arsenical ores of cobalt are roasted and then smelted with limestone or sand, whereby the impurities form a slag, leaving the "cobaltspeiss," which is then dissolved in hydrochloric acid, as in the case of the nickel ores. The final separation of the cobalt from

the accompanying metals is effected by the use of bleachingpowder, which precipitates the cobaltic hydrate.

Cobalt is a slightly reddish-white metal, harder than iron, and of specific gravity 8.5-8.7. It is attracted by magnets, but in a lesser degree than iron. It is slowly attacked by sulphuric and hydrochloric acids, more readily by nitric acid. Cobalt is somewhat used for plating upon other metals, like nickel, but most of it is made into the oxide for use in the manufacture of the pigment smalt. The total annual production of cobalt is about

200 tons.

Compounds of Cobalt.-Two well-defined series of compounds are formed here also: the cobaltous and the cobaltic, corresponding to the ferrous and the ferric. The former of these possess a reddish color when in the hydrated state, but become blue when made anhydrous.

Cobaltous Chloride, CoCl2, is obtained by the solution of cobaltous oxide in hydrochloric acid. It forms red, prismatic crystals which dissolve, yielding a pale pinkish solution. This is well known as the basis of "sympathetic inks;" these leave upon paper almost invisible characters, which when sharply dried become blue.

Cobaltous Oxide, COO, is obtained as a green powder on heating out of contact with air the cobaltous hydrate.

Cobaltous Hydrate, Co(OH)2, is obtained as a rose-red precipitate on the addition of alkalies to hot cobaltous solutions. In cold solutions a blue basic salt is precipitated.

Cobaltous-Cobaltic Oxide, CoО, is a compound corresponding to the magnetic oxide of iron, and is obtained when either of the other oxides of cobalt or the nitrate is heated in the air. It forms a black powder. Cobaltic Oxide, Co2O, corresponding to ferric oxide, is obtained as a dark-brown powder by gently igniting the nitrate.

Cobaltic Hydrate, Co(OH), is obtained as a brownish-black precipitate if an alkaline hypochlorite is added to a cobaltous solution. This is dissolved by sulphuric acid with liberation of oxygen, and by warm hydrochloric acid with liberation of chlorine; cold dilute hydrochloric acid, however, dissolves it with scarcely any evolution of gas, forming CoCl which decomposes on heating, however, into cobaltous chloride and chlorine.

Cobaltous Sulphate, CoSO4.7H2O, forms dark-red, monoclinic prisms. Cobaltous Nitrate, Co(NO3)2.6H2O, forms red, deliquescent prisms. Cobalt Silicates.-When glass of any variety is fused with a cobalt salt a dark-blue color is obtained. This colored glass, when reduced to a powder, is used as a pigment under the name of smalt. The application of ores of cobalt for this purpose appears to date from the sixteenth century. Commercial smalt, made from sand, potashes, and roasted cobalt ores, contains usually from 6 to 16 per cent. of cobalt.

Two other pigments are also obtained from cobalt oxide: Thenara's blue (or cobalt ultramarine), by igniting it with alumina, and Rinmann's green, by igniting it with zinc oxide.