THALLIUM. 407 



of pyrites, either iron or copper, and hence we find it hoth in the 

 sulphur obtained from the first, and hence in many bodies derived 

 from sulphur, and also in the copper obtained from the latter. 

 Spanish copper seems to be especially rich in thallium. The richest 

 pyrites examined was found to yield about 10 ounces to the ton, and 

 the sulphur obtained from the ore about 10 grains to the pound. 

 The sulphur is digested in caustic potassa till dissolved, the dark 

 residue dissolved in sulphuric acid, precipitated by hydrochloric acid, 

 again converted into sulphate, and the metal separated either by zinc 

 or electricity. The easy solubility of the sulphate and the insolubility 

 of the chloride render the separation of the metal on the large scale 

 an easy operation. 



In sulphuric acid factories, the thallium is carried away with the 

 sulphurous acid, but is partly deposited in the flues, and much more 

 might be obtained if the flues were made longer. This flue-dust 

 seems to be the most convenient source of the metal, the quantity 

 however is not large, as Mr. Crookes found only 1 grain in a pound 

 of a seleniferous deposit. 



Thus the thallium may make its appearance in common oil of 

 vitriol and in hydrochloric acid ; five grains have been obtained from 

 a hundred weight of the latter. It may be detected in less than a 

 pound of some kinds of hydrochloric acid by neutralising with ammo- 

 nia, digesting with sulphide of ammonium, dissolving the dark pre- 

 cipitate in nitric and hydrochloric acid, reducing by sulphite of soda, 

 and adding a few drops of iodide of potassium ; a yellow colour or 

 precipitate will be produced. 



Thallium has also been detected in some dark coloured varieties of 

 sulphide of cadmium, and in some salts of copper and bismuth. It 

 has also been detected in tellurium. 



Thallium has a perfect metallic lustre, but tarnishes rapidly in the 

 air, the coating of oxide is readily removed by water, as in the case of 

 most other metals by acids. It softens at a temperature of lOO"-' C, 

 and if kept at that heat, exhibits a crystalline structure, similar to that 

 produced by the continued action of water. 



Heated before the blowpipe, it melts and oxidises, giving off fumes 

 of a white colour with a tint of red, the fumes continue to form after 

 the heat is removed, as in the case of antimony. If a button of the 

 metal be heated in a cupel, and introduced into oxygen, it will burn, 

 the oxide being absorbed into the cupel as with lead. It is slowly 



