1862.] 155 



upon the formation in this manner of an alkaline thallate soluble in 

 water. This acid is also produced in solution when permanganate 

 of potash is added to a soluble salt of oxide of thallium. 



Chloride of Thallium. If a current of dry chlorine is passed over 

 precipitated thallium at a moderate heat, they combine with formation 

 of a volatile chloride, which condenses in the cool part of the tube in 

 the form of a pale-yellow crystalline powder, fusing together in 

 parts to a crystalline lump. Water only partially dissolves this, with 

 production of a white insoluble residue. Dilute hydrochloric acid 

 added to the turbid solution immediately renders it clear; upon 

 evaporating this solution over a water-bath, white crystals of the 

 chloride are deposited. When the nitric-acid solution of thallium or 

 its sulphide is evaporated with an excess of hydrochloric acid, and 

 then more hydrochloric acid added and the evaporation repeated to 

 a syrup, a residue is obtained which is apparently decomposed by 

 water with production of a white precipitate : this is chloride of 

 thallium ; it is insoluble or nearly so in water, but readily soluble in 

 dilute hydrochloric or nitric acid. 



Sulphide of Thallium. When sulphuretted hydrogen is passed 

 through the acid solution of chloride of thallium, a partial precipita- 

 tion of a reddish-brown powder takes place ; this appears to be a com- 

 bination of the chloride and sulphide, and the metal is never entirely 

 removed from solution by this means. The best method of obtaining 

 the sulphide is to precipitate it with sulphide of ammonium in an 

 alkaline solution: unless a large quantity of thallium is present, 

 no immediate effect is produced beyond the darkening of the liquid ; 

 it assumes a brown tint, which becomes rapidly more and more 

 intense, especially upon gently heating it, until the sulphide of 

 thallium separates in the form of a deep-brown heavy precipitate 

 which shows a great tendency to collect together in clots at the 

 bottom of the vessel : this formation of the sulphide is very charac- 

 teristic of the metal. Sulphide of thallium is insoluble in an excess 

 of sulphide of ammonium, ammonia, or cyanide of potassium. Its 

 complete precipitation as sulphide from solutions containing an 

 excess of cyanide of potassium affords a ready means of separating 

 thallium from several metals with which it is frequently associated. 

 It is difficultly soluble in hydrochloric or sulphuric acids, but readily 



