This metal is sparingly distributed in many kinds of iron-arid copper-pyrites, and in some lithia-micas,but occurs to the extent of 17 1/4 per cent. (with about 33 1/4 per cent. of selenium) in a new Swedish mineral named crookesite. It is most conveniently prepared from the flue-dust deposited in the kiln passages of sulphuric acid works which burn pyrites affording the metal; this is boiled several times in water containing sulphuric acid, the solution is concentrated, and, by adding zinc, the thallium is precipitated in shining plates and needles. A second process, which is said to give a purer metal, is as follows: the flue-dust is boiled with water, and hydrochloric acid is added to the concentrated clear solution; the precipitate is washed, gradually dissolved in half its weight of hot sulphuric acid, and heated till nearly all the sulphuric and all the hydrochloric acid is driven off, when the residue is dissolved in water, the solution is dosed with hydrogen sulphide (to throw down antimony, arsenic, bismuth, mercury, and silver), and to the filtrate is added ammonia, with a view of precipitating any alumina or iron; the concentrated filtrate gives pure thallium sulphate in crystals, whence the metal can be procured by electrolysis or by decomposing with zinc.

A third process is described by Bunsen for recovering the metal from crude zmc sulphate containing } per cent. of thallium chloride, which consists in leaving metallic' zinc in contact with the solution, when thallium, cadmium, and copper are precipitated in the metallic condition; the deposit is carefully washed with water, and digested with dilute sulphuric acid, when the thallium and cadmium are dissolved; addition of potassium iodide to this solution causes a separation of the thallium iodide, which, on treatment with potassium cyanide, affords the pure metal. This has a sp. gr. of 11.8, a leaden lustre, a bluish colour, and a crystalline structure; it is malleable, so soft as to mark paper, melts at 554° F. (290° C), and is rapidly dissolved by dilute acids.