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THALLIUM

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Originally appearing in Volume V26, Page 723 of the 1911 Encyclopedia Britannica.
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THALLIUM [See also:

symbol Ti, atomic See also:weight 204.0 (0=16)1, a metallic chemical See also:element. It was discovered in 1861 by See also:Sir See also:William See also:Crookes, who, during a spectroscopic examination of the flue-dust produced in the roasting of seleniferous See also:pyrites occurring at Tilkerode in the Harz, observed a See also:green See also:line See also:foreign to all then known spectra. He concluded that the See also:mineral contained a new element, to which he gave the name of thallium, from OaXX6s, a green twig. Crookes presumed that his thallium was something of the See also:order of See also:sulphur, See also:selenium or See also:tellurium ; but Lamy, who anticipated him in isolating the new element, found it to be a See also:metal. Our knowledge of the See also:chemistry of thallium is based chiefly upon the labours of Crookes. The chemical See also:character of thallium presents striking peculiarities. See also:Dumas once called it the " ornithorhynchus paradoxus of metals." As an elementary substance, it is very similar in its See also:physical properties to See also:lead; it resembles lead chemically inasmuch as it forms an almost insoluble chloride and an insoluble iodide. But the hydroxide of thallium, in most of its properties, comes very See also:close to the See also:alkali metals; it is strongly basic, forms an insoluble chloroplatinate, and an See also:alum strikingly similar to the corresponding See also:potassium compounds. Yet, unlike potassium or lead, it forms a feebly basic sesquioxide similar to manganic See also:oxide, Mn203. Traces of thallium exist in many kinds of pyrites, as used for See also:vitriol-making. The only known mineral of which it forms an essential component is the rare mineral crookesite of Skrikerum, Smaland, See also:Sweden, which, according to See also:Nordenskiold, contains 33.3 per cent. of selenium, 45.8 per cent. of See also:copper, 3.7 per cent. of See also:silver, and 17.2 per cent. of thallium. The best raw materials for the preparation of thallium are the flue-dusts produced industrially in the roasting of thalliferous pyrites and the " chamber muds " accumulating in vitriol-See also:chambers wrought with such pyrites; in both it is frequently associated with selenium.

The flue-dust from the pyrites of Theux, near See also:

Spa (See also:Belgium), according to Bottcher, contains 0.5 to o•75 per cent. of thallium; that of the pyrites of Meggen, according to Carstanjen, as much as 3'5 per cent.; while that of the pyrites of See also:Ruhrort yielded i per cent. of the pure chloride to See also:Gunning. For the extraction of the metal from chamber mud, the latter is boiled with See also:water, which extracts the thallium as the sulphate. From the filtered See also:solution the thallium is precipitated as the chloride by addition of hydrochloric See also:acid, along, in See also:general, with more or less of lead chloride. The mixed chlorides are boiled down to dryness with sulphuric acid to convert them into sulphates, which are then separated by boiling water, which dissolves only the thallium See also:salt. From the filtered solution the thallium is re-covered, as such, by means of pure metallic See also:zinc, or by See also:electrolysis. The (approximately pure) metallic sponge obtained is washed, made compact by See also:compression, fused in a See also:porcelain crucible in an See also:atmosphere of See also:hydrogen, and See also:cast into sticks. Metallic thallium is bluish See also:white; it is extremely soft and almost devoid of tenacity and See also:elasticity. Its specific gravity is 11.86. It fuses at 290° C.; at a white See also:heat it boils and can be distilled in hydrogen See also:gas. Its vapour See also:density at 1728° corresponds to the See also:molecule 1'12. Its salts See also:colour the See also:Bunsen See also:flame a See also:bright green. When heated in See also:air it _is readily oxidized,with the formation of a reddish or See also:violet vapour.

When ex-posed to the air it becomes quickly covered with a film of oxide; the tarnished metal when plunged into water reassumes its metallic lustre, the oxide film being quickly dissolved. When kept in contact with water and air it is gradually converted into hydroxide, T10H. It decomposes water at a red heat, liberating hydrogen and being itself converted into the See also:

hydrate. It is readily soluble in nitric and sulphuric acids, but less so in hydro- chloric. Thallium forms two See also:series of salts: thallous, in which the metal is monovalent; and thallic, in which it is trivalent. In the thallous series many analogies with lead compounds are observed; in the thallic some resemblance to See also:aluminium and See also:gold. Thallous hydroxide, TIOH, is most conveniently prepared by de-composing the solution of the sulphate with baryta water. It crystallizes from its solution in See also:long yellow needles, T10H or T10H+H20, which dissolve readily in water, forming an intensely alkaline solution, which acts as a See also:caustic, and like it greedily absorbs carbonic acid from the atmosphere. Unlike the alkalis, it readily loses its water at See also:loo° C. and even at the See also:ordinary temperature, to See also:form the oxide T120, which is See also:black or black-violet. Thallic oxide, T10 or T1202, was obtained by 0. Rabe (Abst. J.C.S., 1907, ii.

769) by acting with hydrogen peroxide on an alkaline solution of thallous sulphate at See also:

low temperatures, an initial red precipitate rapidly changing into a bluish-black See also:compound. It melts at 720° and decomposes rapidly above 800°, giving See also:oxygen and thallous oxide. Thallous chloride, See also:TIC!, is readily obtained from the solution of any thallous salt, by the addition of hydrochloric acid, as a white precipitate similar in See also:appearance to silver chloride, like which it turns violet in the See also:light and fuses below redness into a (yellow) liquid which freezes into a See also:horn-like flexible See also:mass. It is also formed when the metal is burnt in chloride. The specific gravity of this " horn " thallium is 7.02. One See also:part of the precipitated chloride dissolves at o° C. in 500 parts of water, and in 70 parts at 100° C. It is less soluble in dilute hydrochloric acid. Carbonate of soda solution dissolves it See also:pretty freely. Thallous iodide, Tll, is obtained as a yellow precipitate, which requires 16,000 parts of See also:cold water for its solution, by the addition of potassium iodide to a solution of a thallous salt, or by the See also:direct See also:union of its components. The yellow crystals melt at 190°, and when cooled down assume a red colour, which changes to the See also:original yellow on See also:standing. Thallous bromide, T1Br, is a light yellow crystalline See also:powder; it is formed analogously to the chloride. Thallous fluoride, TIF, forms white glistening octahedra; it is obtained by crystallizing a solution of the carbonate in hydrofluoric acid.

It resembles potassium fluoride in forming an acid salt, TIHF2. Thallous chloroplatinate, TIZPtCl5, readily obtainable from thallous salt solutions by addition of See also:

platinum chloride, is a yellow precipitate soluble in no less than 15,600 parts of cold water. Thallous perchlorate, TIC104, and periodate, T1I04, are interesting inasmuch as they are isomorphous with the corresponding potassium salts. Other instances of the isomorphism of thallous with potassium salts are the nitrates, See also:phosphates, hydrazoates, sulphates, chromates, selenates, and the analogously constituted See also:double salts, and also the oxalates, racemates and picrates. Thallous carbonate, T12CO3, more nearly resembles the See also:lithium compound than any other ordinary carbonate. It is produced by the exposure of thallous hydrate to See also:carbon dioxide, and therefore is obtained when the moist metal is exposed to the air. It forms resplendent See also:monoclinic prisms, soluble in water. Thallous sulphate, TI2SO4, forms rhombic prisms. soluble in water, which melt at a red heat with decomposition, sulphur dioxide being evolved. It unites with sulphuric acid giving an acid salt, T1HSO4.3H2O, and with aluminium, See also:chromium and See also:iron sulphates to form an " alum." It also forms double salts of the type T12SO4(Mg,Fe,ZnSO4)•6H20. Thallous sulphide, TI2S, is obtained as a black precipitate by passing sulphuretted hydrogen into a thallous solution. It is insoluble in water and in the alkalis, but readily dissolves in the mineral acids. On thallium sulphides see H.

Mallon, Abst. J.C.S., 1907, ii. 770. Thallous nitrate, T1NO3, is obtained as white, rhombic prisms by crystallizing a solution of the metal, oxide, carbonate, &c., in nitric acid. Various thallous phosphates are known. The normal salt, T13PO4, is soluble in 200 parts of water, and may be obtained by precipitation. On thallous salts see W. Stortenbeker, Abst. J.C.S., 1907, H. 770. Thallic oxide, TI203, is obtained as a dark reddish powder, insoluble in water and alkalis, by plunging molten thallium into oxygen, or by electrolysing water, using a thallium anode. Titallic hydroxide, Tl(OH)3, is obtained as a See also:

brown precipitate by adding a hot solution of thallous chloride in See also:sodium carbonate to a solution of sodium hypochlorite.

On drying it has the See also:

composition TIO(OH). Hydrochloric acid gives thallous chloride and See also:chlorine; sulphuric acid gives off oxygen; and on See also:heating it first gives the trioxide and afterwards the monoxide. The hydroxide is obtained as brown hexagonal plates by fusing thallic oxide with potash to which a little water has been added. Thallic chloride. TIC13, is obtained by treating the monochloride with chlorine under water; evaporation in a vacuum gives colourless deliquescent crystals of TIC13•See also:H2O. By heating the metal or thallous chloride in chlorine, TICI•TlCI3 is obtained, which on further heating gives3TlC1•TICI3. as a yellowish brown mass. The chloride when anhydrous is a crystalline mass which melts at 24°. It forms several double salts, e.g. with hydrochloric acid and the alkaline chlorides, and also with nitrosyl chloride. The chlorine is not completely precipitated by silver nitrate in nitric acid solution, the ionization apparently not proceeding to all the chlorine atoms. Thallic iodide, TII3, is interesting on See also:account of its isomorphism with See also:rubidium and See also:caesium tri-iodides, a resemblance which suggests the See also:formula TlI(I2) for the salt, in which the metal is obviously monovalent. On the halogen compounds see V. See also:Thomas, Abst.

J.C.S. (1907), ii. 547. Thallic sulphate, See also:

T12(S0,)3.7H2O, and thallic nitrate, Tl(NO3)3.8H2O, are obtained as colourless crystals on the evaporation of a solution of the oxide in the corresponding acid. The sulphate decomposes into sulphuric acid and the trioxide on warming with water, and differs from aluminium sulphate in not forming alums. See also:Analysis.—All thallium compounds volatile or liable to See also:dissociation at the temperature of the flame of a Bunsen See also:lamp impart to such flame an intense green colour. The spectrum contains a bright green of See also:wave-length 5351. From solutions containing it as thallous salt the metal is easily precipitated as chloride, iodide, or chloroplatinate by the corresponding reagents. Sulphuretted hydrogen, in the presence of See also:free mineral acid, gives no precipitate; sulphide of ammonium, from neutral solutions, precipitates TI2S as a dark brown or black precipitate, insoluble in excess of reagent. Thallic salts are easily reduced to thallous by means of solution of sulphurous acid, and thus rendered amenable to the above reactions. The chloroplatinate serves for the quantitative estimation. L.

F. See also:

Hawley employs sodium thiostannate which precipitates thallium as T12SnSa, insoluble in water, and which may be dried on a See also:Gooch See also:filter at 105°. It may be noted that all thallium compounds are poisonous. The atomic weight of thallium was determined very carefully by Crookes, who found T1=204.2 (0=16); this figure was See also:con-firmed by Lepierre in 1893.

End of Article: THALLIUM

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