154 [June 19, 



There is, however, generally a loss in this operation, owing to its 

 rapid oxidation. The metal itself does not appear to be sensibly 

 volatile below a red heat. I have made no special attempts at pre- 

 sent to determine the atomic weight, although from two estimations 

 of the amount of sulphur in the sulphide it appears to be very heavy. 

 The figures obtained did not, however, agree well enough to enable 

 me to speak more definitely on this point, than that I believe it to 

 be above 100. I may mention that I obtained this element in the 

 pure metallic state and exhibited it to several friends as early as 

 January last *, and should then have published an account of it, had 

 it not been for the reasons already mentioned. Thallium is soluble 

 in nitric, hydrochloric, and sulphuric acids, the former attacking it 

 with greatest energy, with evolution of red vapours. 



Oxides of Thallium. Thallium forms two, and probably three 

 oxides : one possessing basic properties, which I shall call the oxide ; 

 another containing more oxygen, possessing acid properties, which 

 may therefore be called thallic acid; and most likely a third, or 

 suboxide, which forms the first portions of the precipitate formed by 

 zinc in solutions of this metal ; the first action being a darkening of 

 the solution, and the production of a deep-brown powder, which by 

 longer contact with zinc turns to a dense black precipitate. 



Upon carefully evaporating the nitric-acid solution upon a water- 

 bath, but not carrying it to dryness, a mass of deliquescent crystals 

 is obtained on cooling, which are decomposed upon addition of water 

 with separation of a white or pale-yellow precipitate, which appears 

 to be a subnitrate, and an acid solution containing nitrate of 

 thallium. If the liquid is evaporated quite to dryness and kept at a 

 temperature of 100 C. for a little time, the nitric acid goes off, and 

 leaves a residue of thallic acid. 



Thallic Acid. This acid is soluble in water, and may be obtained 

 in the crystalline form from its aqueous solution. It then forms 

 crystals, which are permanent in the air, and have an acid reaction to 

 test-paper. The thallates of the alkalies are also soluble in water, 

 and may be prepared by dissolving the acid in the alkali, or by fusing 

 thallium or its oxide with a mixture of alkaline carbonate and nitrate. 

 The method I originally published for extracting thallium was based 



* Vide Chemical News, vol. v. pp. 349, 350. 



