sent. They illustrate, however, two points of theoretical interest-namely, the existence of sulphur-salts which bear to sulphides the same relation which oxygen salts bear to oxides, and the parallelism of composition between these two classes of salts. We place beside each other the empirical formula of the sulphur-salts of potassium and arsenic, and the corresponding oxygen-salts:

342. Quinquisulphide of Arsenic (As,S,).-A sulphide of arsenic corresponding to anhydrous arsenic acid is not known in the free state. The quinquisulphide is known only in combination with sulphides of the metals in sulphur-salts called sulpharseniates. When a solution of sulphide of sodium is digested with some tersulphide of arsenic and sulphur enough to permit the formation of the quinquisulphide, and the solution, after long standing, is concentrated by evaporation and then cooled, large colorless crystals of sulpharseniate of sodium are obtained, which are not changed by exposure to the air. The crystals have the composition indicated by the formula 3Na S,As,S,+ 15H,O. The sulpharseniate, 2Na S,A,S,, may be prepared by saturating the aqueous solution of the corresponding oxygen-salt 2Na,O,As̟,0, with sulphydric acid gas. The sulpharseniates of the alkali-metals, and a few others, are soluble in water; but the greater number of sulpharseniates are insoluble. These insoluble salts are prepared by mixing a solution of an alkaline sulpharseniate with a solution of some salt of the metal whose sulpharseniate is desired. The same parallelism is observable between sulpharseniates and arseniates as between sulpharsenites and arsenites.

266

ANTIMONY.

CHAPTER XVIII.

ANTIMONY.

343. Antimony is found native, both alone and alloyed with other metals, especially with arsenic, nickel, and silver. There exist also a considerable number of minerals which consist of, or contain, large proportions of the compounds of antimony with oxygen and sulphur.

344. All the antimony of commerce is obtained from the mineral tersulphide, Sb,S,. The symbol for antimony is Sb, from the Latin name of the substance, Stibium. This sulphide is very fusible, melting readily in the flame of a candle; it may therefore be separated from the earthy or rocky gangue in which it occurs by simple fusion at a low temperature. The metal is obtained from the sulphide by several different processes:-1. By adding to the melted sulphide iron nails, filings, or scraps; the iron and the antimony change places.

Sb,S,+3Fe 3FeS + 2Sb.

2. By roasting the sulphide of antimony, reduced to a coarse powder, until the greater part of the sulphur has been burnt off and the antimony converted into the oxide; this residue is then mixed into a paste with water, charcoal powder, and carbonate of sodium, or some equivalent reducing flux, and heated in covered crucibles to full redness; the metal sinks to the bottom of the crucible. 3. By fusing together a mixture of sulphide of antimony, the scales which fall from hot iron when it is hammered (an oxide of iron), carbonate of sodium, and charcoal; this process is a sort of combination in a single operation of the two preceding methods. Since the sulphides and oxides of antimony and the metal itself are somewhat volatile at moderate temperatures, it has thus far been found impossible to avoid a considerable loss of metal during the melting, roasting, and reducing of the ore. From one-fifth to one-half of the metal is lost, according to the skill and care of the workmen.

345. The commonest impurities in commercial antimony are

PROPERTIES OF ANTIMONY.

267

sulphur, sodium, arsenic, lead, iron, and copper. These impurities injure the antimony for many of its applications in the arts; and the extensive use of antimonial preparations in medicine renders the removal of the arsenic a point of particular impor

The purification may be effected by fusing the powdered metal, first, with a mixture of sulphide of antimony and carbonate of sodium, and, secondly, with a mixture of carbonate of sodium and nitre. These fusions may be several times repeated; the impurities are either oxidized or converted into sulphides, and enter the slag. Lead, however, cannot be got rid of by these processes; this impurity is removed by fusing the antimony with oxide of antimony; the lead changes places with the antimony in the oxide of antimony, and is converted into litharge.

346. Antimony is a brittle metal, having a bluish-white color, a brilliant lustre, and a highly crystalline structure. The cakes of the commercial metal usually present upon their upper surfaces beautiful stellate or fern-like markings. Like phosphorus and arsenic, it is dimorphous, crystallizing both in rhombohedrons and octahedrons. The specific gravity of the metal is from 6·60 to 6.85; its atomic weight is 122. For a metal, it is a poor conductor of heat and electricity. At 450° it melts, gives off vapors at a low red heat, and takes fire at full redness, burning brilliantly, with evolution of white fumes of the teroxide (Sb,O,). If the antimony is contaminated with arsenic, as is often the case, a garlic odor, due to the presence of this impurity, may be imparted to the vapors.

Exp. 134.-Melt about 0.5 grm. of antimony by heating it on a piece of charcoal before the blowpipe. (See Chapter XX.) Throw the white, glowing globule into the middle of a large tray made of coarse paper; the globule bursts into a multitude of small beads, which fly over the paper, leaving in their trail a white, powdery oxide.

Exp. 135.-Melt a second small fragment of antimony upon charcoal as before, but, instead of throwing it from the coal, allow it to cool there slowly. The globule will, in this case, become covered with an efflorescence of crystals of the oxide.

The metal is not oxidized by exposure to dry or moist air at ordinary temperatures. Nitric acid oxidizes it easily, but does not dissolve it; the insoluble quinquioxide, or some mixed oxide, is formed, according to the strength of the acid employed.

Powdered antimony takes fire when thrown into chlorine gas, and combines very energetically with bromine and iodine. When finely powdered, it is dissolved by boiling chlorhydric acid, with evolution of hydrogen; if a little nitric acid be added to the chlorhydric, the metal dissolves easily, to form a solution of terchloride of antimony (SbCl,). The metal, when in fine powder, is also dissolved readily by solutions of the higher sulphides of sodium and potassium, with formation of sulphantimonites and sulphantimoniates.

347. In spite of the strong tendency of this metal to crystallize, it can be obtained in an amorphous form by the electrolysis of concentrated antimonial solutions. This amorphous antimony always contains, however, 5 or 6 per cent. of terchloride of antimony and a trace of chlorhydric acid; whether these foreign substances are retained mechanically, or not, within the mass, is not clear. The amorphous metal has a dark steel-color, a smooth surface, a comparatively soft texture, a lustrous amorphous fracture and a specific gravity varying from 5.74 to 5.83. When gently heated or sharply struck, the amorphous antimony suddenly manifests a great heat, the temperature rising from 15° to 230° and upwards, and fumes of terchloride of antimony are evolved. After undergoing this peculiar change, the metal approximates to the crystalline variety in structure, density, and color.

348. Antimony enters into the composition of several very valuable alloys. Type-metal is an alloy of lead and antimony, containing about 20 per cent. of antimony. For stereotype plates to of tin is usually added to this alloy. The common white metallic alloys used for cheap teapots, spoons, forks, and like utensils, are variously compounded of brass, tin, lead, bismuth, and antimony; for example, a superior kind of pewter is made of 12 parts tin, 1 part antimony, and a small proportion of copper; Britannia metal is sometimes compounded of equal parts of brass, antimony, tin, bismuth, and lead. The value of antimony in these alloys depends upon the hardness which it communicates to the compounds, without rendering them inconveniently brittle.

With zinc, antimony forms two alloys having a definite crys

ANTIMONY AND HYDROGEN.

269

talline character. The alloy containing 43 per cent. of zinc crystallizes in silver-white needle-like prisms; it answers to the formula Sb Zn,. The alloy containing 33 per cent. of zinc crystallizes in broad plates presenting no similarity to the form of the other alloy; it answers to the formula SbZn. These alloys, especially Sb.Zn,, decompose boiling water with evolution of hydrogen. The crystals of these two alloys are obtained by the method of fusion (§ 194). In each of these crystallized alloys, the crystalline form may be preserved, although the proportions of the ingredients may vary considerably from the exact atomic proportions indicated by their formulæ. Thus needles may be obtained in which the actual proportion of antimony present varies from 35.77 per cent. to 57.24 per cent., the exact atomic proportion being 55.7 per cent.; and the percentage of antimony in the plates may fall as low as 64.57, or may rise as high as 79-42, although 65.07 per cent. is the true atomic proportion. These interesting crystalline alloys strikingly illustrate, therefore, a principle of wide applicability, namely, that a definite crystalline form is not necessarily a guaranty of an unvarying chemical composition.

349. Antimony and Hydrogen.-The composition of the gaseous compound of these two elements is not certainly known, inasmuch as it has never yet been prepared free from admixed hydrogen. When a solution of any salt of antimony is poured into a mixture of zinc and dilute acid which is disengaging hydrogen, the antimony compound is decomposed; one portion of the antimony, and sometimes even the whole of it, is deposited upon the zinc, while another portion usually combines with the hydrogen, and assumes the gaseous state. When this compound gas is passed through a solution of nitrate of silver, a precipitate is produced which has been found to consist of antimonide of silver, SbAg,. Since silver is a metal which replaces hydrogen, atom for atom, it is a natural inference that the gas which has produced this precipitate must have the composition represented by the formula SbH,. This supposition derives strength from the analogous formula of the well-known gases ammonia, NH, phosphuretted hydrogen, PH,, and arseniuretted hyrogen, AsH, Antimoniuretted hydrogen is a colorless gas, inodorous when