201' Mr. R. W. Pearson on the Determination of Bismuth 



formula of quercitrine, are explained by the difference in the 

 quantity of water. 



Buchner recommends for the purification of sulphuric acid from 

 arsenic, the addition of common salt. The hydrochloric acid 

 evolved unites with any arsenious acid present to form terchloride 

 of arsenic, which is easily expelled at a gentle heat. 



XXVI. On the Determination of Bismuth by Weight and by 

 Volume. By R. West Pearson of Manchester^. 



THE method at present employed for the determination of 

 bismuth, consists in treating the solution of the metal with 

 sulphuretted hydrogen, filtering off the precipitated sulphide of 

 bismuth, whicla, after washing with water, is decomposed by 

 digestion with nitric acid. Nitrate of bismuth is thus formed 

 and sulphur liberated. The sulphur is removed by filtration ; 

 the oxide of bismuth is then precipitated from its solution as 

 carbonate of bismuth : upon the first addition of alkaline car- 

 bonate a considerable quantity of the precipitate produced is 

 redissolved. A. Stromeyerf states that the precipitate by car- 

 bonate of alkali is somewhat soluble in excess, but precipitated 

 by caustic alkali. According to L. Laugier J, the precipitate is 

 completely soluble in carbonate of ammonia, partly so in car- 

 bonate of soda, and insoluble in carbonate of potash. According 

 to Berzelius§, however, oxide of bismuth is not soluble in car- 

 bonate of ammonia unless phosphoric acid or arsenic acid is pre- 

 sent. Rose II directs, that to obtain that portion of bismuth 

 which remains in solution after exposure to heat and air, it is 

 necessary to repeat the operations just indicated, i. e. precipitate 

 as sulphide of bismuth, obtain in solution as nitrate, precipitate 

 as carbonate of bismuth, and expose at a warm temperature to 

 the atmosphere for several hours ; after which convert the car- 

 bonate by ignition into oxide of bismuth, in which state weigh. 

 This method, it is evident, is open to a serious objection in the 

 great amount of time consumed in its execution. It is also in- 

 applicable to solutions containing lead or cadmium. Hydro- 

 chloric acid and soluble chlorides must also be absent from the 

 solution. 



R. H. Brett^ found that carbonate and oxide of bismuth 



* Communicated by the Author. 



t Poggendorff's Annalen, vol. xxvi. p. 553. 



X Ann. de Chim. et de Phys. vol. xxxvi. p. 332. 



§ JaJiresber. vol. xii. p. 166. 



II Handb. der Analyt. Chemie, vol. ii. p. 145. 



IT Phil. Mag. vol. x. p. 95, 



