126 THALLIUM. 



and solution of caustic potassa. Concentrated hydro- 

 chloric acid is gradually poured through the funnel- 

 tube, and, after the first reaction has ceased, the distil- 

 lation is continued with aid of heat, as long as osmic 

 acid passes over. It is then, with very careful man- 

 agement on account of the injurious action of the vapor 

 upon the respiratory organs and eyes, dissolved in the 

 solution of potassa, the fluid added to the alkaline so- 

 lution obtained after the fusion of the ore with caustic 

 potassa and nitrate of potassa, and the whole evapo- 

 rated until crystals of red osmate of potassa are 

 formed. The rest of the osmium can be precipitated 

 in the mother liquor by chloride of ammonium. (See 

 No. 70.) 



The dark brownish-red solution in the retort is eva- 

 porated to dryness, the mass again dissolved in hot 

 water, and the solution mixed with a hot saturated 

 solution of chloride of potassium in large excess. The 

 indium, platinum, rhodium, and ruthenium are pre- 

 cipitated as double salts insoluble in the solution, and 

 washed with a saturated solution of chloride of potas- 

 sium. The iron and palladium remain undissolved. 



Kesidue, B. It is brownish-black, earthy, and rich 

 in rhodium, but contains much silica, alumina, gypsum, 

 iron, &c. To separate these impurities it may be fused 

 with lead and litharge, or with several times its weight 

 of carbonate of soda. In the latter case the mass is 

 first washed with hot water, digested with hydrochlo- 

 ric acid, and then treated as the other residue. 



72. THALLIUM. 



I. This element was discovered by Crookes in 18B1, 

 in a seleniferous deposit from a sulphuric acid manu- 

 factory in the Hartz. The name is derived from 



