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Antimony

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ANTIMONY, a bluish-white, exceedingly brittle metal. In its naturally occurring sulphide (stibnite) it has been known from very early times, more especially in Eastern countries, reference to it being made in the Old Testament. Basil Valentine alludes to stibnite in his Triumphal Car of Antimony (c. 1600), and at a later date describes the preparation of the metal.

Native mineral antimony occurs occasionally, and as such was first recognized in 1748. It is usually found in lamellar or granular masses, with a tin-white colour and metallic lustre, in limestone or in mineral veins often in association with ores of silver. Dis tinct crystals are rarely met with ; these are rhombohedral and isomorphous with arsenic and bismuth. Hardness 3-31, specific gravity 6.65-7.72. Sala in Sweden, Allemont in Dauphine, and Sarawak in Borneo may be mentioned as some of the localities for this mineral. Antimony, however, occurs chiefly as the sul phide, stibnite; to a much smaller extent it occurs in combination with other metallic sulphides in the minerals wolf sbergite, boulan gerite, bournonite, pyrargyrite, etc. For the preparation of metallic antimony the crude stibnite being readily fusible (m.p. 540°C) 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 coal, care being taken to pre vent 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 in refining. For rich ores the method of roast ing the sulphide with scrap-iron is sometimes employed ; carbon, salt and sodium sulphate being used to slag the iron. The crude antimony is fused with stibnite to remove iron and then with a flux of potash and antimony sulphide (potassium thioantimonite) to remove sulphur in the form of thioantimoniate. By these oper ations pure antimony is obtained. Antimony has an atomic weight of 121•77 (Symbol Sb, atomic number 51, isotopes 121-123) and is included in the same natural family of elements as nitrogen, phosphorus, arsenic and bismuth.

Antimony combines readily with many other metals to form alloys, some of which find extensive application in the arts. Type metal (q.v.) is an alloy of lead with antimony and tin, to which occasionally a small quantity of copper or zinc is added. An alloy of tin and antimony forms the basis of Britannia-metal (q.v.), small quantities of copper, lead, zinc or bismuth being added. 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 630.5°C (Heycock and Neville), and boils at about 1,500°C. Its specific heat is 0•0523 (H. Kopp). The vapour density of antimony at 1,572°C is 10.74, and at 1,640°C 9.78 (V. Meyer), so that the antimony molecule is less complex than the molecules of the elements phosphorus and arsenic. An amorphous modifi cation 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 6.2 2, melting at 614°C and containing of antimony (F. Herard, 1888). Another form of the metal, known as explosive antimony, was discovered by G. Gore (1858), on electrolysing a solution of anti mony 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 anti mony trichioride (from 6 to 20a% 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 (see ALLOTROPY).

Pure antimony is quite permanent in air at ordinary tempera tures, but when heated in air or oxygen it burns, forming the trioxide. It decomposes steam at a red heat, and burns 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 normal sulphate 3 being formed. Nitric acid oxidizes antimony, the oxide 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, etc.) .

Detection and Estimation.

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 which the black stain of antimony 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 addi tion of water, with formation of insoluble basic salts, soluble in solutions of tartaric acid. Antimony may be estimated quantita tively 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. It may also be determined volumetrically by titrating an antimonious salt, in the presence of an excess of sodium bicarbonate as a buffer, with a standard solution of iodine.

Inorganic Compounds.

Antimoniuretted hydrogen or sti bine, may be prepared by the action of hydrochloric acid on an alloy of antimony and zinc, by the action of nascent hydrogen on antimony compounds or by dropping water on to aluminium antimonide. As prepared by the first two 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 decom posed by heat into its constituent elements. With silver nitrate solution it gives a black precipitate of silver antimonide, it is decomposed by the halogen elements and also by sulphuretted hydrogen.

Oxides and Acids.

There are three known oxides of anti mony, the trioxide which is capable of combining with both acids and bases to form salts, the tetroxide and the acidic pentoxide Antimony trioxide occurs as the minerals val entinite and senarmontite, and can be artificially prepared by burning antimony in air, 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 crystal line forms, either octahedral or prismatic. It is insoluble in sul phuric and nitric acids, but is readily soluble in hydrochloric and tartaric acids and in solutions of the caustic alkalis. Antimony tetroxide, formed by strongly heating in air either the trioxide or pentoxide or by oxidizing the metal with nitric acid and of ter wards igniting to redness, is a non-volatile white powder, 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, a pale yellow powder, is obtained by repeatedly evaporating antimony with nitric acid and heating the resulting antimonic acid to a temperature not above 275° C. On being heated strongly it gives up oxygen and forms the tetroxide. It is insoluble in water, but dissolves slowly in hydrochloric acid. It possesses a feebly acidic character, giving metantimoniates when heated with alkaline carbonates.

Orthoantimonic acid, obtained by the decomposition of its potassium salt with nitric acid (A. Geuther), or by the addition of water to the pentachloride, is a white powder almost insoluble in water and nitric acid, and when heated is first con verted into metantimonic acid, and then into the pent oxide Pyroantimonic acid, (the metantimonic acid of E. Fremy), is obtained by decomposing antimony pen tachloride with hot water, and drying the precipitate so obtained at loo° 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 and M,Sb207. Metantimonic acid, obtained by heating orthoantimonic acid to 175° C, is a white powder almost insoluble in water, but slowly hydrated into the ortho-acid.

Halogen Compounds.

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 f orma tion of basic salts. Antimony trichloride ("Butter of Antimony"), is obtained by burning the metal in chlorine, by distilling antimony with excess of mercuric chloride, or by fractional distillation of antimony tetroxide or trisulphide in hydrochloric acid. It is a colourless deliquescent solid of specific gravity 3.06; it melts at 73.2° C to a colourless oil; and boils at 223°. It is soluble in alcohol, and also in a small quantity of water ; but with an excess of water it gives a precipitate of various oxychlo rides, known as powder of algaroth (q.v.). The trichloride is used in the preparation of tartar emetic, as a bronzing solution for gun barrels and as a caustic in medicine. Antimony pentachloride, SbC1,, prepared by heating the trichloride in a current of chlorine, 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. Antimony triflu oride, is obtained by dissolving the trioxide in aqueous hydrofluoric acid or by distilling antimony with mercuric fluoride. The double compound known as "antimony salts" is used in dyeing. The pentafluoride SbF, results when metanti monic acid is dissolved in hydrofluoric acid and it forms an amorphous gummy mass, which is decomposed by heat. Tartar emetic, potassium antimonyl tartrate, (SbO) made from the trioxide and cream of tartar, is used medicinally and as a mordant in dyeing although for the latter purpose it is partly superseded by the double oxalate or lactate. On precipitat ing antimony trichloride or tartar emetic in acid solution with sulphuretted hydrogen, an orange-red precipitate of the hydrated trisulphide 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 anti mony trisulphide with basic sulphides, livers of antimony are obtained. These thioantimonites are usually prepared by fusing their components together, and are dark powders which are less soluble in water the more antimony they contain. They are used in the vulcanizing of rubber and in the preparation of matches. The so-called golden sulphide consists mainly of Sb2S, obtained together with sulphur by acidifying solutions of alkali thioanti monates. It is doubtful whether antimony pentasulphide, 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 con taining antimonic acid, is a chemical entity or merely a mixture of tri- and tetra-sulphide with sulphur. It forms a fine dark orange powder insoluble in water, but readily soluble in aqueous solutions of the caustic alkalis and alkaline carbonates. This so-called pentasulphide is employed in the vulcanization of rubber.

Organic

organic compounds containing antimony are known. By distilling an alloy of antimony and sodium with methyl iodide, mixed with sand, trimethylstibine, is obtained; this combines with excess of methyl iodide to form tetramethylstibonium iodide, which on treatment with moist silver oxide gives the corresponding tetramethylstibonium hydroxide, a strong base obtained in deliquescent crystals, of alkaline reaction, and ab sorbing carbon dioxide readily. The Grignard (q.v.) reaction has facilitated the production of organo-antimonials (H. Hibbert, 1906). Methyl magnesium iodide and antimony trichloride yield trimethylstibine which combines with bromine, forming trimethylstibine dibromide. On heating, this dibromide loses methyl bromide and gives rise to dimethylstibine bromide This product absorbs bromine forming a tribromide which undergoes demethylation on gentle heating so that it yields methylstibine dibromide. By this progressive demethylation de rivatives of primary and secondary stibines have been obtained (G. T. Morgan and G. R. Davies, 1926). Corresponding anti mony compounds containing the ethyl group are known, as is also a triphenylstibine, which is prepared from anti mony trichloride, sodium and monochlorbenzene. See G. T. Morgan, Organic Compounds of Arsenic and Antimony (1918) .

acid, obtained, water, heated and powder