ture, but it was found necessary to give up this process, since the metal obtained was always alloyed with a large quantity of iron.

Assay of Ores of Antimony.-Ores of antimony which do not contain sulphur are assayed by fusion with 3 parts of black flux, a very high temperature being avoided, because of the volatility of the metal. Care must be taken that the

button be not broken in extracting it from the crucible.

The best method of assaying the sulphide of antimony consists in fusing it at a moderate heat, in an earthen crucible, with 4 parts of Liebig's cyanide of potassium.

It is obvious that the volatility of the metal must prevent the attainment of anything more than an approximation to the amount of antimony present in the

ore.

§ 295. Pharmaceutical Preparations of Antimony.-Several preparations of antimony are used in medicine.

The most important of these is tartar-emetic, the double tartrate of antimony and potassa, the description of which falls within the province of organic chemistry.

Antimonium calcinatum, or diaphoretic antimony, is prepared by deflagrating the tersulphide with 3 parts of nitre, and washing the fused mass with water; the residue contains an acid antimoniate of potassa.

Antimonii cinis (antimony-ash) is an oxy-sulphide, prepared by roasting the tersulphide in air.

The substance termed antimonii oxydum, or antimonii oxydum nitro-muriaticum, is prepared by dissolving the tersulphide in hydrochloric or nitro-hydrochloric acid, precipitating by water, and washing the precipitate as long as the washings have any acid reaction; it consists of teroxide of antimony with a little terchloride.

ARSENIC.

Sym. As. Eq. 75. Sp. Gr. 5.75.

§ 296. Although, in its combinations, this element more nearly resembles the non-metallic bodies, we have, according to the usual custom, placed it among the metals.

Arsenic is rather widely diffused in nature, sometimes in the metallic state, or as a sulphide, but generally associated with the ores of iron, nickel, cobalt, and

copper.

The mineral known as arsenical pyrites (mispickel) usually contains arsenic, iron, and sulphur, in the proportions expressed by the formula FeS,, FeAs. Red and yellow orpiment will be spoken of under the sulphides of arsenic. Preparation.-Arsenic is prepared either from mispickel or from arsenious

acid.

The arsenical pyrites is strongly heated in earthen cylinders, with fragments of iron, which retain the whole of the sulphur, while the arsenic sublimes into other cylinders, serving as receivers; it is purified by redistilling with a little charcoal.

In order to obtain arsenic from arsenious acid, it is only necessary to mix the latter with about twice its weight of black flux, and to heat the mixture in a Hessian crucible, which is covered with a second crucible, kept cool in order that the arsenic may be condensed; the two crucibles should be luted together, a small aperture being left for the escape of the carbonic oxide.

Properties.-Arsenic has a steel-gray color, and metallic lustre; it is crystal

line in texture, and exceedingly brittle. It is converted into vapor at about 572° F. (300° C.), without previously fusing; it may, however, be fused in a sealed tube. If the vapor of arsenic be allowed to condense slowly, the metal is deposited in brilliant rhombohedral crystals. The density of the vapor of arsenic is 10.39.

When exposed to air, arsenic is tarnished and assumes a dull black color, probably becoming covered with a film of suboxide; when placed in contact with water, air being allowed free access, it is gradually converted into arsenious acid. When heated in air, this metal is oxidized, and produces white fumes of arsenious acid, at the same time exhaling a peculiar alliaceous odor, ascribed by some to the vapor of the metal itself, by others to a suboxide of arsenic.

Arsenic burns, when heated in oxygen, with a pale blue flame, producing arsenious acid. It is not capable of decomposing water at any temperature, nor in presence of acids.

Arsenic is not attacked by hydrochloric acid, but nitric acid dissolves it readily, arsenious or arsenic acid being produced, according to the concentration of the acid; when the ordinary nitric acid of the laboratory is employed, the former is usually found in solution. Chlorine combines energetically with arsenic, the powdered metal taking fire spontaneously in this gas.

Metallic arsenic does not produce symptoms of poisoning in animals till a considerable period after its administration; it is probably first converted into arsenious acid.

The substance known as fly-powder consists of a mixture of metallic arsenic with arsenious acid, and is prepared by exposing the metal to air in presence of

water.

Arsenic exhibits in its combinations a remarkable similarity to phosphorus; thus, with hydrogen, oxygen, and chlorine, it forms compounds analogous to those formed by that element.

$297. The existence of an inferior oxide is regarded as doubtful; some chemists contend that the product of the slow oxidation of arsenic by exposure to moist air, is merely a mixture of metallic arsenic and arsenious acid; it cer tainly yields these products when subjected to heat.

ARSENIOUS ACID, AsO, (commonly called ARSENIC, or

White Arsenic.)

Preparation.-Arsenious acid is prepared by roasting arsenical pyrites with free access of air, when the arsenic is oxidized, and the arsenious acid is condensed in large chambers.

It is also obtained as a by-product in roasting certain ores, especially those of tin and cobalt.

The arsenious acid thus obtained is purified by sublimation.

Properties.-Arsenious acid, when freshly prepared, forms transparent colorless, vitreous masses, which, after some time, become opaque externally, the opacity afterwards extending throughout the mass, until it resembles a fragment of porcelain.

1 The equivalent of arsenic is sometimes considered as 37.5, when arsenious acid would be As。0, and arsenic acid As20.

The vitreous and opaque varieties of arsenious acid differ considerably in some of their properties.

The specific gravity of the vitreous acid is 3.74, that of the opaque variety 3.70.

When the vitreous acid is reduced to powder, it is converted into the opaque variety.

At the ordinary temperature, the vitreous acid is three times as soluble in water as that which is opaque.

Heat is capable of causing the opaque acid to become vitreous, while cold reverses the change; hence, by long boiling with water, the opaque acid is converted into the vitreous modification, and, as the solution cools, part of the arsenious acid in the opaque condition is deposited; thus these two forms of arsenious acid are generally found in the same solution.

When vitreous arsenious acid is dissolved in boiling dilute hydrochloric acid, it is deposited on cooling in regular octohedra of the opaque variety, the deposi tion of each crystal being said to be attended by a flash of light, which is not the case if the crystals be redissolved in hydrochloric acid, or if the opaque variety be originally employed.

Arsenious acid is dimorphous, and has been obtained by sublimation in thin prisms. It volatilizes below a red heat, without previously fusing; it may, however, be fused, if heated in a sealed tube.

Vapor of arsenious acid is inodorous, and has the specific gravity 13.85. If it be condensed in a receiver which attains a pretty high temperature, a layer of vitreous arsenious acid is formed, whilst, if deposited in a slow current of air, the acid is obtained in fine octohedral crystals.

Arsenious acid is sparingly soluble in cold water, but, as implied above, more so in hot water; 1000 parts of boiling water dissolve about 80 parts of arsenious acid, and the solution, after cooling to 60° F. (15°.5 C.), retains only 30 parts. If water at 60° F. be mixed with arsenious acid in powder, only 2 parts are dissolved by 1000 of water.1

The aqueous solution has a feeble acid reaction to test-papers. It is much more soluble in hydrochloric acid. When arsenious acid is boiled with concentrated hydrochloric acid, terchloride of arsenic is formed and volatilized.

When boiled with nitric (or better, nitro-hydrochloric) acid, arsenious is converted into arsenic acid. Solution of ammonia is capable of dissolving it, and of depositing it again in crystals. Arsenious acid is easily reduced to the metallic state by hydrogen or carbon at a high temperature.

This acid is bibasic, forming salts, which are termed arsenites. It is a most virulent poison.

Uses. Arsenious acid is used in the manufacture of glass, where it serves to oxidize any (prot-) oxide of iron which may be present, converting it into sesquioxide, which does not color the glass so deeply. It also enters into the composition of various pigments and coloring matters. Arsenious acid is extensively employed for destroying vermin, and for preventing the smut in grain.

$298. Arsenite of Potassa (2KO.AsO) is obtained by dissolving arsenious acid in solution of potassa.

It crystallizes with difficulty, and is deliquescent; its solution has an alkaline

reaction."

The amount dissolved, however, depends, to a remarkable extent, upon the duration of the contact between the arsenious acid and the water.

2 According to Pasteur, there exist two other arsenites of potassa, KO.HO.2ASO, and KO.ASO3.

Rose has obtained insoluble arseniates of magnesia and the alkalies, by fusing ignited arseniate of magnesia and ammonia with alkaline carbonates.

ARSENITE OF COPPER, 2CuO.AsO,. (Scheele's green.)

This substance is precipitated in a hydrated state when sulphate of copper is added to a solution of a neutral arsenite.

It is prepared on the large scale by dissolving 64 lbs. of carbonate of potassa and 2 lbs. of arsenious acid in 3 gallons of water, and gradually adding the liquid to a boiling solution of 6 lbs. of sulphate of copper in 9 gallons of water, with continual stirring.

The shade of color may be modified by varying the quantity of arsenious acid. Arsenite of copper dissolves readily in acids, and in ammonia. When heated, the arsenious acid is expelled, oxide of copper being left. It is a very active poison.

Uses.-Scheele's green is employed largely by paper-stainers, and in oil-painting. It is also used to a lamentable extent in coloring ornaments of confectionery, and grave accidents frequently arise from this cause.

The pigment known as Schweinfurt green is a compound of arsenite with acetate of copper, CuO.A,3(2CuO.AsO,), and is prepared by mixing together boiling solutions of equal weights of arsenious acid and of acetate of copper, the ebullition being maintained for some time after mixing.

ARSENIC ACID, ASO,.

§ 299. Preparation.—Arsenious acid is heated with a considerable excess of nitric acid and a small quantity of hydrochloric; 8 parts of arsenious acid may be dissolved in 24 parts of nitric, and 2 parts of hydrochloric acid. The solution is evaporated to a syrupy consistence, and pretty strongly heated, to expel the excess of acid.

Properties.-Arsenic acid is a white deliquescent solid; when strongly heated, it first fuses, and is decomposed into arsenious acid and oxygen. This acid is very soluble in water, but dissolves slowly after it has been dried; the aqueous solution deposits crystals if sufficiently evaporated, and set aside. These crystals contain hydrated arsenic acid. It is easily decomposed by deoxidizing agents; sulphurous acid reduces it to arsenious acid.

Arsenic acid is tribasic; its salts much resemble those of the tribasic phosphoric acid with which it is isomorphous; like these latter, the arseniates may contain 1 or 2 eqs. of basic water.

Tribasic arseniate of potassa, with 3 eqs. of fixed base (3KO.AsO,), is prepared by adding an excess of potassa to arsenic acid, and crystallizes in fine deliquescent needles.

Common arseniate of potassa (2KO.HO. ASO,) is prepared by neutralizing potassa with arsenic acid; it is deliquescent, and has not been crystallized.

Acid arseniate of potassa, KO.2HO ASO,, may be obtained by adding an excess of arsenic acid to the preceding salt; it crystallizes in forms derived from the octohedron, and is unaltered in air.

The corresponding arseniates of soda have been obtained.

The common arseniate, 2NaO.HO.AsO,, crystallizes with 26 eqs. of water; the crystals effloresce in air.

Solutions of the arseniates give, with nitrate of silver, a brick-red precipitate of the tribasic arseniate of silver, 3AgO.AsO,, the solution being neutral or acid after the reaction, according to the amount of fixed base present.

Arsenic acid is capable of forming insoluble compounds with binoxide of tin, as may be shown by oxidizing an alloy of tin and arsenic with nitric acid, when a considerable quantity of arsenic may be found in the residue.

ARSENIURETTED HYDROGEN, ASH,

$300. This compound is prepared by dissolving an alloy of tin and arsenic in hydrochloric acid, with the aid of heat; or by acting upon zinc with dilute sulphuric acid in presence of arsenic. The gas obtained by these methods always contains free hydrogen.

Properties.-Arseniuretted hydrogen is a colorless gas having a sickly alliaceous odor; its sp. gr. is 2.69. It may be liquefied at -22° F. (-30° C.) It is somewhat soluble in water; 5 vols. of water dissolve about 1 vol. of the gas. Arseniuretted hydrogen is inflammable, and burns with a livid flame, yielding arsenious acid and water; if it be burnt in a bell-jar, with a limited supply of air, a brown deposit (said to be a solid compound of arsenic with hydrogen) is formed simultaneously with the above products. A similar brown deposit is formed when the gas is kept for a long time over water.

If a porcelain plate be depressed into the flame of arseniuretted hydrogen, so as partially to cut off the supply of air, the hydrogen alone is oxidized, and a spot of arsenic is deposited upon the porcelain.

This gas is very readily decomposed into its elements by heat; if the tube through which arseniuretted hydrogen is passed be heated to redness with a spirit-lamp, a lustrous mirror of metallic arsenic is deposited at some distance from the heated portion.

Chlorine decomposes arseniuretted hydrogen with great energy, emitting a brilliant light. The gas is absorbed by several metallic salts (sulphate of copper, nitrate of silver, &c.), producing, in some cases, dark precipitates, the nature of which is not known with certainty.

It is a very poisonous gas, and great care should be taken not to respire it. Arseniuretted hydrogen is sometimes prepared in order to furnish indications of the presence of arsenic (Marsh's test); we defer the details of the process until the detection of arsenic comes under consideration.

TERCHLORIDE OF ARSENIC, AsCl。.

To prepare this substance, arsenic is gently heated in a retort, through which a current of dry chlorine is passed; or it may be obtained by distilling the metal with 6 parts of chloride of mercury (corrosive sublimate).

It is a colorless liquid, heavier than water, and boiling at 270° F. (132° C.) The density of its vapor is 6.3.

Terchloride of arsenic is decomposed by water, yielding hydrochloric and arsenious acids :-1

AsCl,+3HO=AsO2+3HCl.

It is said to be poisonous.

No pentachloride of arsenic has yet been obtained.

A compound of terchloride of arsenic with 3 eqs. of chloride of sulphur has been obtained.

A hydrated terchloride of arsenic is produced when the terchloride is mixed with a small quantity of water, or when arsenious acid is dissolved in hydrochloric acid.