ANTIMONY (symbol Sb, atomic weight 120·2), one of the metallic chemical elements, included in the same natural family of the elements as nitrogen, phosphorus, arsenic, and bismuth. Antimony, in the form of its sulphide, has been known from very early times, more especially in Eastern countries, reference to it being made in the Old Testament. The Arabic name for the naturally occurring stibnite is “kohl”; Dioscorides mentions it under the term στίμμι, Pliny as stibium; and Geber as antimonium. By the German writers it is called Speissglanz. Basil Valentine alludes to it in his Triumphal Car of Antimony (circa 1600), and at a later date describes the preparation of the metal.
Native mineral antimony is occasionally found, and as such was first recognized in 1748. It usually occurs as lamellar or glanular masses, with a tin-white colour and metallic lustre, in limestone or in mineral veins often in association with ores of silver. Distinct crystals are rarely met with; these are rhombohedral and isomorphous with arsenic and bismuth; they have a perfect cleavage parallel to the basal plane, c (111), and are sometimes twinned on a rhombohedral plane, e (110). Hardness 3–312 specific gravity 6·65–6·72. Sala in Sweden, Allemont in Dauphiné, and Sarawak in Borneo may be mentioned as some of the localities for this mineral.
Antimony, however, occurs chiefly as the sulphide, stibnite; to a much smaller extent it occurs in combination with other metallic sulphides in the minerals wolfsbergite, boulangerite, bournonite, pyrargyrite, &c. For the preparation of metallic antimony the crude stibnite is first liquated, to free it from earthy and siliceous matter, and is then roasted in order to convert it into oxide. After oxidation, the product is reduced by heating with carbon, care being taken to prevent any loss through volatilization, by covering the mass with a layer of some protective substance such as potash, soda or glauber salt, which also aids the refining. For rich ores the method of roasting the sulphide with metallic iron is sometimes employed; carbon and salt or sodium sulphate being used to slag the iron. Electrolytic methods, in which a solution of antimony sulphide in sodium sulphide is used as the electrolyte, have been proposed (see German Patent 67973, and also Borcher’s Electro-Metallurgie), but do not yet appear to have been used on the large scale.
Antimony combines readily with many other metals to form alloys, some of which find extensive application in the arts. Type-metal is an alloy of lead with antimony and tin, to which occasionally a small quantity of copper or zinc is added. The presence of the antimony in this alloy gives to it hardness, and the property of expanding on solidification, thus allowing a sharp cast of the letter to be taken. An alloy of tin and antimony forms the basis of Britannia-metal, small quantities of copper, lead, zinc or bismuth being added. It is a white metal of bluish tint and is malleable and ductile. For the linings of brasses, various white metals are used, these being alloys of copper, antimony and tin, and occasionally lead.
Antimony is a silvery white, crystalline, brittle metal, and has a high lustre. Its specific gravity varies from 6·7 to 6·86; it melts at 432° C. (Dalton), and boils between 1090-1600° C. (T. Carnelley), or above 1300° (V. Meyer). Its specific heat is 0·0523 (H. Kopp). The vapour density of antimony at 1572° C. is 10·74, and at 1640° C. 9·78 (V. Meyer, Berichte, 1889, 22, p. 725), so that the antimony molecule is less complex than the molecules of the elements phosphorus and arsenic. An amorphous modification of antimony can be prepared by heating the metal in a stream of nitrogen, when it condenses in the cool part of the apparatus as a grey powder of specific gravity 6·22, melting at 614° C. and containing 98-99% of antimony (F. Hérard, Comptes Rendus, 1888, cvii. 420).
Another form of the metal, known as explosive antimony, was discovered by G. Gore (Phil. Trans., 1858, p. 185; 1859, p. 797; 1862, p. 623), on electrolysing a solution of antimony trichloride in hydrochloric acid, using a positive pole of antimony and a negative pole of copper or platinum wire. It has a specific gravity of 5·78 and always contains some unaltered antimony trichloride (from 6 to 20%, G. Gore). It is very unstable, a scratch causing it instantaneously to pass into the stable form with explosive violence and the development of much heat. Similar phenomena are exhibited in the electrolysis of solutions of antimony tribromide and tri-iodide, the product obtained from the tribromide having a specific gravity of 5·4, and containing 18-20% of antimony tribromide, whilst that from the tri-iodide has a specific gravity of 5·2-5·8 and contains about 22% of hydriodic acid and antimony tri-iodide.
The atomic weight of antimony has been determined by the analysis of the chloride, bromide and iodide. J. P. Cooke (Proc. Amer. Acad., 1878, xiii. i) and J. Bongartz (Berichte, 1883, 16, p. 1942) obtained the value 120, whilst F. Pfeiffer (Ann. Chim. et Phys. ccix. 173) obtained the value 121 from the electrolysis of the chloride.
Pure antimony is quite permanent in air at ordinary temperatures, but when heated in air or oxygen it burns, forming the trioxide. It decomposes steam at a red heat, and burns (especially when finely powdered) in chlorine. Dilute hydrochloric acid is without action on it, but on warming with the concentrated acid, antimony trichloride is formed; it dissolves in warm concentrated sulphuric acid, the sulphate Sb2(SO4)3 being formed. Nitric acid oxidizes antimony either to the trioxide Sb4O6 or the pentoxide Sb2O5, the product obtained depending on the temperature and concentration of the acid. It combines directly with sulphur and phosphorus, and is readily oxidized when heated with metallic oxides (such as litharge, mercuric oxide, manganese dioxide, &c.). Antimony and its salts may be readily detected by the orange precipitate of antimony sulphide which is produced when sulphuretted hydrogen is passed through their acid solutions, and also by the Marsh test (see Arsenic); in this latter case the black stain produced is not soluble in bleaching powder solution. Antimony compounds when heated on charcoal with sodium carbonate in the reducing flame give brittle beads of metallic antimony, and a white incrustation of the oxide. The antimonious compounds are decomposed on addition of water, with formation of basic salts.
Antimony may be estimated quantitatively by conversion into the sulphide; the precipitate obtained is dried at 100° C. and heated in a current of carbon dioxide, or it may be converted into the tetroxide by nitric acid.
Antimony, like phosphorus and arsenic, combines directly with hydrogen. The compound formed, antimoniuretted hydrogen or stibine, SbH3, may also be prepared by the action of hydrochloric acid on an alloy of antimony and zinc, or by the action of nascent hydrogen on antimony compounds. As prepared by these methods it contains a relatively large amount of hydrogen, from which it can be freed by passing through a tube immersed in liquid air, when it condenses to a white solid. It is a poisonous colourless gas, with a characteristic offensive smell. In its general behaviour it resembles arsine, burning with a violet flame and being decomposed by heat into its constituent elements. When passed into silver nitrate solution it gives a black precipitate of silver antimonide, SbAg3. It is decomposed by the halogen elements and also by sulphuretted hydrogen. All three hydrogen atoms are replaceable by organic radicals and the resulting compounds combine with compounds of the type RCl, RBr and RI to form stibonium compounds.
There are three known oxides of antimony, the trioxide Sb4O6 which is capable of combining with both acids and bases to form salts, the tetroxide Sb2O4 and the pentoxide Sb2O5. Antimony trioxide occurs as the minerals valentinite and senarmontite, and can be artificially prepared by burning antimony in air; by heating the metal in steam to a bright red heat; by oxidizing melted antimony with litharge; by decomposing antimony trichloride with an aqueous solution of sodium carbonate, or by the action of dilute nitric acid on the metal. It is a white powder, almost insoluble in water, and when volatilized, condenses in two crystalline forms, either octahedral or prismatic. It is insoluble in sulphuric and nitric acids, but is readily soluble in hydrochloric and tartaric acids and in solutions of the caustic alkalies. On strongly heating in air it is converted into the tetroxide. The corresponding hydroxide, orthoantimonious acid, Sb(OH)3, can be obtained in a somewhat impure form by precipitating tartar emetic with dilute sulphuric acid; or better by decomposing antimonyl tartaric acid with sulphuric acid and drying the precipitated white powder at 100° C. Antimony tetroxide is formed by strongly heating either the trioxide or pentoxide. It is a nonvolatile white powder, and has a specific gravity of 6·6952; it is insoluble in water and almost so in acids—concentrated hydrochloric acid dissolving a small quantity. It is decomposed by a hot solution of potassium bitartrate. Antimony pentoxide is obtained by repeatedly evaporating antimony with nitric acid and heating the resulting antimonic acid to a temperature not above 275° C.; by heating antimony with red mercuric oxide until the mass becomes yellow (J. Berzelius); or by evaporating antimony trichloride to dryness with nitric acid. It is a pale yellow powder (of specific gravity 6·5), which on being heated strongly gives up oxygen and forms the tetroxide. It is insoluble in water, but dissolves slowly in hydrochloric acid. It possesses a feeble acid character, giving metantimoniates when heated with alkaline carbonates.
Orthoantimonic acid, H3SbO4, is obtained by the decomposition of its potassium salt with nitric acid (A. Geuther); or by the addition of water to the pentachloride, the precipitate formed being dried over sulphuric acid (P. Conrad, Chem. News, 1879, xl. 198). It is a white powder almost insoluble in water and nitric acid, and when heated, is first converted into metantimonic acid, HSbO3, and then into the pentoxide Sb2O5. Pyroantimonic acid, H4Sb2O7 (the metantimonic acid of E. Frémy), is obtained by decomposing antimony pentachloride with hot water, and drying the precipitate so obtained at 100° C. It is a white powder which is more soluble in water and acids than orthoantimonic acid. It forms two series of salts, of the types M2H2Sb2O7 and M4Sb2O7. Metantimonic acid, HSbO3, can be obtained by heating orthoantimonic acid to 175° C., or by long fusion of antimony with antimony sulphide and nitre. The fused mass is extracted with water, nitric acid is added to the solution, and the precipitate obtained washed with water (J. Berzelius). It is a white powder almost insoluble in water. On standing with water for some time it is slowly converted into the ortho-acid.
Compounds of antimony with all the halogen elements are known, one atom of the metal combining with three or five atoms of the halogen, except in the case of bromine, where only the tribromide is known. The majority of these halide compounds are decomposed by water, with the formation of basic salts. Antimony trichloride (“Butter of Antimony”), SbCl3, is obtained by burning the metal in chlorine; by distilling antimony with excess of mercuric chloride; and by fractional distillation of antimony tetroxide or trisulphide in hydrochloric acid solution. It is a colourless deliquescent solid of specific gravity 3·06; it melts at 73·2° C. (H. Kopp) to a colourless oil; and boils at 223° (H. Capitaine). It is soluble in alcohol and in carbon bisulphide, and also in a small quantity of water; but with an excess of water it gives a precipitate of various oxychlorides, known as powder of algaroth (q.v.). These precipitated oxychlorides on continued boiling with water lose all their chlorine and ultimately give a residue of antimony trioxide. It combines with chlorides of the alkali metals to form double salts, and also with barium, calcium, strontium, and magnesium chlorides. Antimony pentachloride, SbCl5 is prepared by heating the trichloride in a current of chlorine. It is a nearly colourless fuming liquid of unpleasant smell, which can be solidified to a mass of crystals melting at −6°C. It dissociates into the trichloride and chlorine when heated. It combines with water, forming the hydrates SbCl5·H2O and SbCl5·4H2O; it also combines with phosphorus oxychloride, hydrocyanic acid, and cyanogen chloride. In chloroform solution it combines with anhydrous oxalic acid to form a compound, Sb2Cl8(C2O4), which is to be considered as tetra-chlorstibonium oxalate 
(R. Anschütz and Evans, Annalen, 1887, ccxxxix. 235). Antimonyl chloride, SbOCl, is produced by the decomposition of one part of the trichloride with four parts of water. Prepared in this way it contains a small quantity of the unaltered chloride, which can be removed by ether or carbon bisulphide. It is a white powder insoluble in water, alcohol and ether. On heating, it is converted into the oxychloride Sb4O5Cl2 (Sb2O3·SbOCl). Antimony oxychloride, SbOCl3, is formed by addition of the calculated quantity of water to ice-cooled antimony pentachloride, SbCl5 + H2O = SbOCl3 + 2HCl. It forms a yellowish crystalline precipitate which in moist air goes to a thick liquid. Compounds of composition, SbOCl3·2SbCl5 and SbO2Cl·2SbOCl3, have also been described (W. C. Williams, Chem. News. 1871, xxiv. 234).
Antimony tribromide, SbBr3, and tri-iodide, SbI3, may be prepared by the action of antimony on solutions of bromine or iodine in carbon bisulphide. The tribromide is a colourless crystalline mass of specific gravity 4·148 (23°), melting at 90° to 94° C. and boiling at 275·4° C. (H. Kopp). The tri-iodide forms red-coloured crystals of specific gravity 4·848 (26°), melting at 165° to 167° C. and boiling at 401° C. By the action of water they give oxybromides and oxyiodides SbOBr, Sb4O5Br2, SbOI. Antimony penta-iodide, SbI5, is formed by heating antimony with excess of iodine, in a sealed tube, to a temperature not above 130°C. It forms a dark brown crystalline mass, melting at 78° to 79° C., and is easily dissociated on heating. Antimony trifluoride, SbF3, is obtained by dissolving the trioxide in aqueous hydrofluoric acid or by distilling antimony with mercuric fluoride. By rapid evaporation of its solution it may be obtained in small prisms. The pentafluoride SbF5 results when metantimonic acid is dissolved in hydrofluoric acid, and the solution is evaporated. It forms an amorphous gummy mass, which is decomposed by heat. Oxyfluorides of composition SbOF and SbOF3 are known.
Two sulphides of antimony are definitely known, the trisulphide Sb2S3 and the pentasulphide Sb2S5; a third, the tetrasulphide Sb2S4, has also been described, but its existence is doubtful. Antimony trisulphide, Sb2S3, occurs as the mineral antimonite or stibnite, from which the commercial product is obtained by a process of liquation. The amorphous variety may be obtained from the crystalline form by dissolving it in caustic potash or soda or in solutions of alkaline sulphides, and precipitating the hot solution by dilute sulphuric acid. The precipitate is then washed with water and dried at 100° C., by which treatment it is obtained in the anhydrous form. On precipitating antimony trichloride or tartar emetic in acid solution with sulphuretted hydrogen, an orange-red precipitate of the hydrated sulphide is obtained, which turns black on being heated to 200° C The trisulphide heated in a current of hydrogen is reduced to the metallic state; it burns in air forming the tetroxide, and is soluble in concentrated hydrochloric acid, in solutions of the caustic alkalis, and in alkaline sulphides. By the union of antimony trisulphide with basic sulphides, livers of antimony are obtained. These substances are usually prepared by fusing their components together, and are dark powders which are less soluble in water the more antimony they contain. These thioantimonites are used in the vulcanizing of rubber and in the preparation of matches. Antimony pentasulphide, Sb2S5, is prepared by precipitating a solution of the pentachloride with sulphuretted hydrogen, by decomposing “Schlippe’s salt” (q.v.) with an acid, or by passing sulphuretted hydrogen into water containing antimonic acid. It forms a fine dark orange powder, insoluble in water, but readily soluble in aqueous solutions of the caustic alkalis and alkaline carbonates. On heating in absence of air, it decomposes into the trisulphide and sulphur.
An antimony phosphide and arsenide are known, as is also a thiophosphate, SbPS4, which is prepared by heating together antimony trichloride and phosphorus pentasulphide.
Many organic compounds containing antimony are known. By distilling an alloy of antimony and sodium with mythyl iodide, mixed with sand, trimethyl stibine, Sb(CH3)3, is obtained; this combines with excess of methyl iodide to form tetramethyl stibonium iodide, Sb(CH3)4I. From this iodide the trimethyl stibine may be obtained by distillation with an alloy of potassium and antimony in a current of carbon dioxide. It is a colourless liquid, slightly soluble in water, and is spontaneously inflammable. The stibonium iodide on treatment with moist silver oxide gives the corresponding tetramethyl stibonium hydroxide, Sb(CH3)4OH, which forms deliquescent crystals, of alkaline reaction, and absorbs carbon dioxide readily. On distilling trimethyl stibine with zinc methyl, antimony tetra-methyl and penta-methyl are formed. Corresponding antimony compounds containing the ethyl group are known, as is also a tri-phenyl stibine, Sb(C6H5)3, which is prepared from antimony trichloride, sodium and monochlorbenzene. See Chung Yu Wang, Antimony (1909).
Antimony in Medicine.—So far back as Basil Valentine and Paracelsus, antimonial preparations were in great vogue as medicinal agents, and came to be so much abused that a prohibition was placed upon their employment by the Paris parlement in 1566. Metallic antimony was utilized to make goblets in which wine was allowed to stand so as to acquire emetic properties, and “everlasting” pills of the metal, supposed to act by contact merely, were administered and recovered for future use after they had fulfilled their purpose. Antimony compounds act as irritants both externally and internally. Tartar emetic (antimony tartrate) when swallowed, acts directly on the wall of the stomach, producing vomiting, and after absorption continues this effect by its action on the medulla. It is a powerful cardiac depressant, diminishing both the force and frequency of the heart’s beat. It depresses respiration, and in large doses lowers temperature. It depresses the nervous system, especially the spinal cord. It is excreted by all the secretions and excretions of the body. Thus as it passes out by the bronchial mucous membrane it increases the amount of secretion and so acts as an expectorant. On the skin its action is that of a diaphoretic, and being also excreted by the bile it acts slightly as a cholagogue. Summed up, its action is that of an irritant, and a cardiac and nervous depressant. But on account of this depressant action it is to be avoided for women and children and rarely used for men.
Toxicology.—Antimony is one of the “protoplasmic” poisons, directly lethal to all living matter. In acute poisoning by it the symptoms are almost identical with those of arsenical poisoning, which is much commoner (See Arsenic). The post-mortem appearances are also very similar, but the gastro-intestinal irritation is much less marked and inflammation of the lungs is more commonly seen. If the patient is not already vomiting freely the treatment is to use the stomach-pump, or give sulphate of zinc (gr. 10–30) by the mouth or apomorphine (gr. 120 – 110) subcutaneously. Frequent doses of a teaspoonful of tannin dissolved in water should be administered, together with strong tea and coffee and mucilaginous fluids. Stimulants may be given subcutaneously, and the patient should be placed in bed between warm blankets with hot-water bottles. Chronic poisoning by antimony is very rare, but resembles in essentials chronic poisoning by arsenic. In its medico-legal aspects antimonial poisoning is of little and lessening importance.