438 [Feb. 19, 



" On Thallium." By WILLIAM CROOKES, Esq. Communi- 

 cated by Professor STOKES, Sec. R.S. Received February 



5, 1863. 



(Abstract.) 



After discussing the occurrence and distribution of the new metal 

 in different parts of the globe, the author proceeds to describe the 

 method adopted by him for extracting it from its ore. Thalli- 

 ferous pyrites is distilled at a bright red heat, in quantities of about 

 1 cwt. at a time, in cast-iron retorts. The resulting sulphur, vary- 

 ing from 13 to 17 per cent, of the pyrites taken, is then dissolved 

 in aqueous caustic soda, which leaves the sulphide of thallium as 

 an insoluble black precipitate ; this is filtered off, dissolved in acids, 

 and the thallium precipitated in the form of iodide. This is then 

 converted into sulphate, and the metal reduced from the solution by 

 electrolysis. It is obtained in the coherent form by fusion under 

 cyanide of potassium. 



The physical characteristics of thallium are then described. In 

 appearance it most resembles tin and cadmium, but has a distinct 

 colour of its own ; it has a brilliant metallic lustre, and is susceptible 

 of taking a very high polish ; it oxidizes in the air with almost the 

 rapidity of an alkaline metal, but when coated with oxide, the metal 

 may be freely handled and exposed to the air with scarcely any 

 further change. An oxidized surface applied to the tongue is very 

 biting and caustic, and has a sweetish metallic taste. It is the 

 softest known metal admitting of free exposure to the atmosphere, 

 being scratched by soft lead with the greatest ease. It makes a 

 dark blue mark upon paper, rapidly turning yellow, which in the 

 course of a few hours nearly fades out, but can be restored with 

 sulphide of ammonium. It has little tenacity, is very malleable, 

 and may be readily pressed into wire. 



The specific gravity of thallium varies from 11 '81 to 11 -91, and 

 it is probably capable of still greater condensation. 



When freshly prepared, thallium wire is perfectly amorphous, 

 but when kept in water it gradually assumes a superficial crystalline 

 appearance : this effect is immediately produced when thallium in 

 wire, ingot, or plate, tarnished or clean, is boiled in water. 



Its melting-point is 550 F., being between bismuth and lead, 





