DETECTION OF ARSENIC. 131 



lamp is gradually applied, commencing a little above the por- 

 tion occupied by the flux, &c. The heat is then gradually 

 raised, until the glass and its contents become red, while the 

 tube is held steadily in one direction, the open end being 

 inclined upwards. The crust which forms, possesses the fol- 

 lowing characters — 'The surface next the tube is almost 

 exactly like polished steel, being a little darker in colour but 

 equal in brilliancy and polish ; and the inner surface is either 

 brilliantly chrystalline to the naked eye, like cast-iron, or has 

 a dull grayish colour, but appears chrystalline before a com- 

 mon magnifier.' This crust may be converted into white 

 oxide by diminishing the heat of the spirit lamp, and chasing 

 it up and down in the tube, until small octahedral crystals are 

 formed of adamantine lustre. This mode was proposed by 

 Dr. Turner. It would swell this notice far beyond its proper 

 length to comment upon the various modifications which have 

 been proposed for this process of reduction, I shall therefore 

 refer to Dr. Christison for the more minute account of it, and 

 proceed to explain the chemical action which takes place in 

 the process for reduction. If metallic arsenic be subjected to 

 the process, no other efiect is produced by the carbonaceous 

 alkaline matter mixed with it, than to reduce the small portion 

 of brown sub-oxide, which is apt to exist with it, and the metal 

 is at once sublimed by the heat, forming the crust before 

 spoken of. But if arsenious acid, or arsenic acid, be present, 

 the acid combines .with the alkaline base, forming an arsenite 

 or arseniate, which is less volatile than the metal or its acids, 

 and it is thus retained long enough to afford the carbon, an 

 opportunity to unite with the oxygen of the acid, passing off 

 in the form of carbonic acid, while tiie metal is sublimed as 

 already described. The arsenic is not all sublimed by any of 

 these processes as has been proved by the experiments of 

 many accurate analysts. When the sulphuret of arsenic is 

 exposed in the reducing tube, the sulphur is separated from the 

 arsenic, and combines with the alkali of the flux, the carbon 

 present preventing the arsenic just liberated from being con- 

 verted into arsenious acid, by rapidly seizing its oxygen as fast 

 as acquired, and allowing the metal to be sublimed in its 

 uncombined form. A portion of undecomposed sulphuret may 

 be sublimed along with the metal, if the heat be applied too 



