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CHARACTERS OF THE COMPOUNDS OF URANIUM.

(741) CHARACTERS OF THE COMPOUNDS OF URANIUM.-I. The uranous salts have a green colour, and have a strong tendency to form double salts with salts of the alkaline metals which contain the same acid as themselves. In solutions of the uranous salts, ammonia and the alkalies give a gelatinous, blackish-brown precipitate of hydrated oxide: this precipitate absorbs oxygen and becomes yellow from the formation of sesquioxide of uranium, which unites with the excess of alkali. Sulphuretted hydrogen produces no precipitate; but sulphide of ammonium occasions a black deposit of sulphide of uranium. Oxalate of ammonium gives a greenish-white precipitate of uranous oxalate. Solutions of the green salts of uranium absorb oxygen rapidly, and are converted by nitric acid into uranic salts, even without the aid of heat.

2.-The uranic salts are yellow. Their solutions give with ammonia a yellow precipitate, consisting of uranate of ammonium : with ferrocyanide of potassium they yield a hair-brown precipitate. By the action of ammonia they are distinguished at once from the compounds of copper, which give a blue solution on the addition of an excess of ammonia, though they yield a precipitate with the ferrocyanide similar in colour to that furnished by the salts of uranium. Sulphuretted hydrogen produces no precipitate, but sulphide of ammonium gives a yellowish-brown sulphide. Carbonates of the alkaline metals give a yellow granular precipitate, soluble in excess of the precipitant; these precipitates are double carbonates of uranium and of the alkaline metal employed. With infusion of nut-galls a dark-brown precipitate is produced.

(742) Estimation of Uranium.-Uranium is usually estimated in the form of protoxide, to which it is reduced by heating the sesquioxide to redness in a glass tube in a current of hydrogen ; the tube must be sealed up whilst full of hydrogen, and weighed in this condition, to prevent the oxide from reabsorbing oxygen from the air.

Uranium is separated from the alkalies by converting it into a uranic salt by nitric acid, if not already in that condition, and then precipitating it in the form of yellow uranate of ammonium. If barium, strontium, calcium, or magnesium be present, the addition of sulphuric acid separates the first two in the form of sulphates; if calcium or magnesium be present, the solution is filtered from the precipitate, the filtrate evaporated to dryness, and then heated with alcohol of specific gravity o'900; the sulphates of calcium and magnesium remain unacted upon, whilst the uranic sulphate is dissolved.

URANIUM-IRON-METEORITES.

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Aluminum, glucinum, zinc, cobalt, and nickel may be separated from uranium by adding acid-carbonate of potassium in excess to the acidulated solution: a double carbonate of potassium and uranium remains in the liquid, whilst the earths, and other metallic oxides, are precipitated. For the success of this experiment it is necessary, if salts of ammonium be present, that they should be expelled, by evaporating the solution to dryness and igniting the residue, before effecting the precipitation of the various bases with the acid-carbonate of potassium.

§ IV. IRON: Fe"=56, or Fe=28. Sp. Gr. 7.844.

(743) Condition of Iron in Nature.-IRON is more extensively diffused than any other metal: not only is it abundant in the inorganic creation, but it is an essential constituent in the blood of the vertebrate animals.

Iron has been occasionally found in the native form accompanying the ores of platinum; but when it occurs in the metallic state it is generally met with in the meteoric masses associated with nickel, cobalt, and small quantities of other metals, among which are copper, manganese, and chromium.* Some of these masses which have fallen in an ignited state from the atmosphere are of very considerable size. One discovered in Siberia, by Pallas, weighed 1600 lb., and a block found in the district of Chaco-Gualamba, in South America, is estimated at between 13 and 14 tons weight. These extraordinary bodies are unimportant

as sources of iron.

Aerolites, or meteoric stones, may be subdivided into three principal groups, the first of which consists of metallic masses, and these are the most common: the second variety contains no metallic iron, but consists often of crystalline minerals; and the third not uncommon form is composed of a mixture of the metallic and earthy variety in the same specimen. These different kinds of aërolites are inclosed in a thin crust or rind of a few hundredths of an inch in thickness, presenting a glossy, pitch-like, or veined surface. The crystalline minerals which have been observed are of a basaltic nature, and consist of olivine, varieties of augite and leucite, anorthite and labradorite; in addition to these, chrome iron, tinstone, magnetic iron ore, and magnetic pyrites, besides nickeliferous metallic iron.

The masses of meteoric iron themselves also display crystalline structure. When a polished surface of one of these metallic masses is immersed in nitric acid, the different portions of the surface are unequally acted upon, as was first noticed by Widmannstatt; and a series of lines crossing each other in three different directions become developed; between them are broad shallow spaces, less deeply etched, and narrow bands between these retain their polish and resist the acid; these bands contain more nickel than the rest of the

mass.

The origin of these meteorites is unknown; but it is an opinion generally

The ores of iron are numerous. The most valuable are the following:

3

1.—Magnetic Iron Ore, or Loadstone (FeÐ,Fе¿Ð ̧; Sp.Gr. 5'09). -This is found in enormous masses, or even mountains, amongst the primary formations. Much of the best Swedish iron is obtained from this material, which is also abundant in North America. Occasionally it is found in detached octohedral crystals. Coal is absent in those formations in which this mineral occurs; hence charcoal is the fuel ordinarily employed in smelting it. This fuel contains a smaller amount of ash than coal; fewer impurities are therefore introduced by it during the smelting than when coal is used; and as the ore itself is generally very pure, the metal which it furnishes is of excellent quality. The iron sand found at Nellore, in India, and employed in the manufacture of wootz, consists chiefly of magnetic oxide of iron.

2.-Specular Iron Ore, or Fer Oligiste; Sp. Gr. 5'2.—This is an anhydrous sesquioxide of iron (Fe): it occurs in the primary rocks. The principal part of the celebrated Elba iron, and also a large quantity of Russian and of Swedish iron, are obtained from this source. Charcoal is in this case also the fuel employed.

3.-Red hæmatite (Fe,,, sp. gr. about 5'0) is another form of the anhydrous sesquioxide: it is sometimes found massive; but more generally in fibrous crystalline nodules. This ore is largely raised in Lancashire and in some parts of Cornwall. It is seldom smelted alone; but it forms a valuable addition to the clay iron-stone of the coal-measures.

4.-Brown Hæmatite (2 Fe,,, 3 H2O); Sp. Gr. about 3'9.— This is a hydrated sesquioxide of iron, which generally occurs in

received, that they are asteroïds or planetary dust, fragments of which from time to time come within the sphere of the earth's attraction: these, by friction in their rapid flight through the earth's atmosphere, become ignited, and ultimately reach the surface of the earth.

Amongst the constituents of these meteorites twenty-two elementary substances have been found, but no element not previously known to be of terrestrial origin has been discovered. The following are the meteoric elements, partly in the earthy, partly in the metallic portions:

The metallic portions consist chiefly of native iron, which contains sulphur, phosphorus, carbon, manganese, magnesium, nickel, cobalt, tin, and copper.

fibrous or in compact masses. It is, however, also met with in the oölitic strata, in some parts of France, in the form of rounded masses termed pea-iron ore, mixed with a small proportion of clay. Much of the French iron is obtained from this source. Brown hæmatite is readily soluble in hydrochloric acid; it is less refractory in the furnace than the preceding variety. The brown hæmatite, when roasted, becomes porous from the loss of its water, and is thus rendered more manageable. Mixed with variable proportions of earth or clay, and sometimes with oxide of manganese, this oxide of iron forms the varieties of umber and ochres. It occurs principally in the secondary and tertiary deposits.

5.-Spathic Iron, or Carbonate of Iron (FeO3); Sp. Gr. 3.8. -This is found in crystalline masses often combined with carbonate of magnesium and with a considerable proportion of manganese, as in the Saxony ores. Much of the so-called natural steel

is made from this ore.

6.-Clay ironstone is the chief source of the enormous quantity of iron manufactured in Great Britain. It is an impure carbonate of iron, containing generally from 30 to 33 per cent. of metallic iron, mingled with varying proportions of clay, oxide of manganese, lime, and magnesia. This argillaceous ironstone occurs in bands broken up into nodules, or in continuous seams, from two to fourteen inches thick, alternating with beds of coal, clay, shale, or limestone, in the coal-measures diffused over large areas in South Staffordshire, South Wales, and some other parts of Great Britain. It is also found in the United States, and in Bohemia and other countries of central Europe. It has a specific gravity ranging between 27 and 3'47.

7.-The black band of the Scotch coal-fields is also a carbonate of iron, but the principal foreign matter in this mineral, which often amounts to 25 or 30 per cent., is of a bituminous or combustible nature.

8.—A siliceous ironstone has been found abundantly in the oölite in the neighbourhood of Northampton. It yields an inferior iron, owing to the presence of a large quantity of phosphates in the ore.

9.-Another, but comparatively an unimportant ore, of a brown colour, known as bog-iron ore, is a mixture of hydrated sesquioxide and phosphate of iron in variable proportions. It occurs in marshy alluvial districts, near the surface.

Iron pyrites (FeS2), though a very abundant mineral, is wrought only for the sake of its sulphur, because the iron which it furnishes is not pure enough for use.

(744) SMELTING OF CLAY IRONSTONE.-After the ore has been broken up into masses about the size of two fists, it is roasted, in order to expel water and carbonic acid; the mass is thus left in a porous state, highly favourable to its subsequent reduction in the furnace. The roasting is sometimes performed in kilns, but usually in heaps in the open air. If this operation is to be effected in the open heap, a plat of ground is levelled and covered with a layer of coal in lumps to the depth of 10 or 12 inches; this is succeeded by alternate layers of the mineral and of small coal. The quantity of coal required in the case of the black band is often very small, as the ore itself frequently contains sufficient inflammable matter to continue burning when once well lighted. The heap, when finished, is 14 or 15 feet wide, 8 or 10 high,

FIG. 345

and of great length. The fire is kindled at the windward extremity, and d allowed to spread gra

dually through the mass. This preliminary operation occupies some months for its completion. The roasted ore is then ready for the smelting.

The blast furnace employed for this purpose is represented in section in fig. 345. The internal cavity in shape resembles a long narrow funnel inverted upon the mouth of another shorter funnel. These furnaces are usually about 50 feet high, and from 14 to 17 feet in diameter in the widest part of the cavity. The lowest portion, P, or neck of the funnel, is

termed the crucible or hearth, and is made of very refractory gritstone. In the front, 8 or 10 inches from the floor н, is a longitudinal aperture above the tymp-stone, L, for the overflow of the slag, and on the sides are the openings for the tuyères, 1, 1, or