detection of Poisonous Compounds. 333 



delicacy, should never be neglected ; but where such advan- 

 tages are not within reach, a more simple process, even 

 though slightly inferior in delicacy, must always be preferred. 

 Hence, if in Reinsclr's and Marshes processes, the sources 

 of error inseparable from each were exactly balanced, still 

 Reinsclr's method would be the one most generally applicable : 

 for notwithstanding the improvements and simplifications 

 introduced into Marshes process by Drs. Fresenius and Von 

 Babo,* by M. M. Flandin and Danger,t M. Blondlot,J M. 

 Lassaigne,§ Berzelius, and others, still apparatus, peculiarly 

 adapted to the processes, and of somewhat complicated 

 construction, is required in every case ; and whether the 

 arseniuret of hydrogen be burnt in the open air as proposed 

 in the first instance by Marsh, or in connection with a 

 cooled receiver, as is practised by M. M. Danger and Flan- 

 din ; or the gas be passed into a solution of nitrate of silver ; 

 or it be decomposed whilst passing through a tube heated to 

 redness, as recommended by Berzelius and Liebig, still, in each 

 instance, much practical tact, and some experience are re- 

 quisite to ensure success. But the sources of error in Marshes 

 process do in reality far out-number those that can possibly 

 enter into that of Reinsch. In the first place, any form of 

 Marsh's apparatus having once had arseniuret of hydrogen 

 evolved in it, can never again be employed with confidence, 

 owing to the great difficulty, if not impossibility, of ridding the 

 exit tube and stop-cock of all traces of arsenic. The objec- 

 tion, at one time so strongly urged against Marsh's method, 

 on account of the supposed difficulty of separating and dis- 

 tinguishing arsenic from antimony deposited in this process 

 from their respective hydrurets, need scarcely be alluded to, 

 now that most simple methods of separating the two metals 



* Annalen der Chimie und Pharmacie, 1844. xlix. 291. 

 f Journal de Chimie Medicale, 1841, p. 413. 



X Coraptes Rendus, July 1845. § Comptes Rendus, Dec. 1845. 



