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thallium, compounds, lead and acid

THALIA, the blooming one,' one of the nine Muses. She was the Muse of comedy and pastoral poetry, and is usually represented with the comic mask and the shep herd's crook in her hand. One of the Graces was also called Thalia. See GRACES.

a metallic element' discov ered by Sir William Crookes (1862) in a de posit obtained from the lead chambers of a sulphuric acid works at Tilkerrode in the Harz. On examining this deposit with the spectroscope the discoverer observed a single sharp and bnl liant green line, which was afterward shown to be characteristic of this element. Crookes gave the element the name of thallium from the Greek thallus, a green twig. Thallium is found in many natural sulphides such as those of iron, copper, zinc, bismuth, etc. An important mineral containing it is Crookesite, a compound of sulphur, copper, silver and thallium. When iron or zinc sulphide is burned in the process of making sulphuric acid, the thallium burns to its oxide which collects in the flues or in the lead chambers. To obtain metallic thallium from this flue dust, it is dissolved in dilute sulphuric acid, filtered, and hydrochloric acid added. The slightly soluble thallium chloride separates. This is changed to the sulphate,

purified at the various elements accompanying thallium and the thallium sulphate decomposed by electrolysis or by action of zinc. Thallium, symbol Tl, has an atomic weight of 204.18, spe cific gravity 11.19 and fuses at 561 F. A freshly cut surface has a brilliant silver white lustre which is quickly lost by the oxidizing action of the air. It is softer than lead and is malleable. The metal dissolves readily in sul phuric or nitric acids, but only slightly in hydrochloric acid. It forms two classes of compounds: the thallous compounds derived from the oxide T120, and the thallic compounds from The salts of the first class re semble the corresponding salts of potassium and sodium. The chloride, however, resem bles those of silver and lead in its insolubility in water. Thallium compounds give a green color to a non-luminous name. They are very poisonous, resembling lead in physiological ac tion. Thallium and its compounds are used in the manufacture of thallium glass,. the high refractive power of which makes it valuable in the preparation of optical instruments and of artificial gems.