THALLIUM. 127 



" green," because its existence was first recognized by 

 an intense green line, appearing in the spectrum of a 

 flame in which thallium was volatilized. It was at 

 first suspected to be a metalloid, but further examina- 

 tion proved it to be a true metal. It was first obtained 

 in a distinct metallic form by Crookes towards the 

 end of the year 1861, and about the same time by 

 Lamy, who prepared it from a deposit of the lead 

 chamber of M. Kuhlmann, of Lille. 



Thallium is very widely diffused as a constituent of 

 iron and copper pyrites, though it never constitutes 

 more than the 4000th part of the bulk of the ores. It 

 also occurs in some specimens of blende and calami ne, 

 sulphide of cadmium, native sulphur; in bismuth, mer- 

 cury, and antimony ores, and in the manufactured pro- 

 ducts from these. It is also found in some specimens of 

 lepidolite and mica, and in certain brines, as those of 

 Nauheim, in which it was found associated with chlo- 

 rides of caseium and rubidium. 



II. The easiest mode of extracting the metal consists 

 in treating the thalliferous dust deposited in the flues 

 of the sulphuric acid works before they enter the 

 chamber, with an equal weight of boiling water, draw- 

 ing off the clear liquor, and treating the undissolved 

 portion again in like manner. The clear liquids are 

 next mixed with a large excess of strong hydrochloric 

 acid, by which a precipitate of impure chloride of 

 thallium is obtained. This is then washed, pressed, 

 and decomposed by treating it with an equal weight 

 of concentrated sulphuric acid. The acid sulphate of 

 thallium thus obtained is dissolved in about 20 parts 

 of water, filtered, ajad again precipitated as tolerably 

 pure chloride by the addition of hydrochloric acid in 

 excess. The precipitate is washed, pressed, and again 

 converted into sulphate by adding about two-thirds 

 of its weight of oil of vitriol and heating until all the 

 hydrochloric acid is expelled ; a dense liquid is thus 



