228 M. Bucliner on the Purification of Sulphuric Acid. 



plain the statement of Graham*, that the wire gauze of the safety 

 lamp soaked with solution of alkali becomes much more imper- 

 vious to the flame. 



Bucliner nine years ago gave a method for freeing sulphuric 

 acid from arsenic, which was based on the ready conversion of 

 arscnious acid into the more volatile chloride of arsenic by means 

 of hydrochloric acid, and which simply consisted in passing a 

 current of II CI through heated sulphuric acid, Bussy and 

 Buignet, and, independently of them, Bloxamf, found that sul- 

 phuric acid could not be purified in this way from arsenic. On 

 going into the experiments of Bussy and Buignet, Buchner found 

 the cause to be that the arsenic was present as arsenic, and not as 

 arsenious acid. Now arsenic acid in solution is but imperfectly 

 converted into chloride of arsenic. Souchay, under Fresenius's 

 direction, has recently found that from a boiling mixture of 

 arsenic and hydrochloric acids very little arsenic is volatilized ; 

 and indeed it is on this fact that Fresenius and Babo's method 

 for removing, by means of chlorate of potash and hydrochloric 

 acid, organic matters from solutions containing arsenic is based. 

 Buchner J accordingly proposes, as a modification of his method, 

 to convert any arsenic acid which may be present first into arse- 

 nious acid. This is best effected by heating the acid to be 

 purified with a few pieces of charcoal ; sulphurous acid is libe- 

 rated, which in a few minutes reduces the arsenic acid so com- 

 pletely to arsenious acid that every trace may be subsequently 

 removed by passing a current of hydrochloric acid through. 



Delafontaine§ has determined the atomic weight of thorium, 

 and communicated some considerations on the formula of thoria. 

 Berzelius, in 1829, had found a series of numbers for the atomic 

 weight of thorium agreeing but imperfectly with each other, and 

 the mean of which (calculated according to the modern atomic 

 weights for sulphur, barium, and potassium ; for Berzelius's de- 

 termination was made with the sulphate of thoria and potash) is 

 5938. Delafontaine used for the preparation of thoria the 

 minerals thorite and orangite ; and the method he used is that 

 employed by Marignac for the treatment of cerite. The pow- 

 dered mineral was moistened with water and made into a semifluid 

 paste with sulphuric acid, by which so much heat was produced 

 as to expel most of the excess of sulphuric acid. The residual 

 mass was heated until all acid was driven off. The residue was then 

 dissolved in cold water and filtered. The solution was next con- 



* Poggenrtorff's Annalen, vol. xxxvii. p. 36". 



t Journal of the Chemical Society, vol. xv. p. 52. 



% Liebig's Annalen, May 1864. 



§ Archives des Sciences Physiques et Naturelles, vol. xviii. p. 343. 



