M. Berthelot on Acetylene. 187 



Hydrochloric acid and the protochlorides give with the same 

 solutions a white precipitate of chloride of thallium, resembling 

 chloride of silver, but slightly soluble in water ; it is, further, 

 little soluble in ammonia, and unaltered by the light. 



Hydrosulphuric acid is without action on pure neutral or 

 acid liquids ; but if they are alkaline, a voluminous black pre- 

 cipitate of sulphide of thallium is formed, which collects on 

 the bottom of the vessel, and is insoluble in an excess of the 

 precipitant. 



Potash, soda, and ammonia do not expel oxide of thallium 

 from its combination with sulphuric or nitric acids. 



Natural condition and extraction. — Thallium cannot be con- 

 sidered as very rare in nature. It exists, in fact, in many kinds 

 of pyrites which at present are worked in considerable masses, 

 principally for the manufacture of sulphuric acid. I will men- 

 tion more especially the Belgian pyrites of Theux, Namur, and 

 Phillippeville. I have also found it in mineralogical specimens 

 from Nantes and Bolivia. 



Thallium might be extracted from these pyrites; but it is 

 much more simple to prepare it from the deposits in the lead 

 chambers, where it accumulates in pretty considerable quan- 

 tities during the manufacture of sulphuric acid. 



It is from these thalliferous deposits that I extracted, by a 

 method which I describe in my memoir, the chloride of thallium, 

 which was the starting-point of my investigation. 



The metal can be extracted from one of its saline compounds, 

 either by the electric current, or by precipitation with zinc, or 

 by reduction with charcoal at a high temperature. It may also 

 be separated from its chloride by potassium or sodium with the 

 aid of heat ; in the latter case the reaction is very brisk. 



A small ingot weighing 14 grammes was isolated by a pile of 

 a few of Bunsen's elements — at first from the chlorides which I 

 had originally obtained, then from the crystallized sulphate 

 formed directly by dissolving this thallium in pure sulphuric 

 acid. 



This memoir is not presented to the Academy as a complete 

 research on thallium. My principal object has been to show the 

 new metal, and some of its principal salts. In my next commu- 

 nication I shall try to fill up some of the links in its history. 



Berthelot has made* the following additional observations on 

 acetylene f. He finds that it is decomposed by the induction- 

 spark, with separation of carbon, and that mixed with chlorine it 



* Comptes Rendiis, May 12, 1862, 

 t Phil, Mag. vol. xxi. p. 358. 



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