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Account of a Method of separating Small Quantities of Arsenic 

 from Substances with which it may he mixed. By James 

 Marsh, Esq. of the Royal Arsenal, Woolwich. (Com- 

 municated to the Society of Arts of London).* 



Notwithstanding the improved methods that have of late 

 been invented of detecting the presence of small quantities of ar- 

 senic in the food, in the contents of the stomach, and mixed with 

 various other animal and vegetable matters, a process was still 

 wanting for separating it expeditiously and commodiously, and 

 presenting it in a pure unequivocal form for examination by the 

 appropriate tests. Such a process should be capable of detecting 

 arsenic not only in its usual state of white arsenic or arsenious 

 acid, but likewise in that of arsenic acid and of all the compound 

 salts formed by the union of either of these acids with alkaline 

 substances. It ought, also, to exhibit the arsenic in its reguline 

 or metallic state, free from the ambiguity which is sometimes 

 caused by the use of carbonaceous reducing fluxes. It appeared 

 to me, that these objects might be attained by presenting to the 

 arsenic, hydrogen gas in its nascent state : the first action of 

 which would be to deoxygenate the arsenic ; and the next, to 

 combine with the arsenic, thus deoxygenated, into the well-known 

 gas called arsenuretted hydrogen. Being thus brought to the 

 gaseous state, the arsenic would spontaneously (so to speak) 

 separate itself from the liquor in which it was before dis- 

 solved, and might be collected for examination by means of any 

 common gas apparatus ; thus avoiding the trouble, difficulty, 

 and ambiguity of clarification and other processes whereby li- 

 quors, suspected of containing arsenic, are prepared for the ex- 

 hibition of the usual tests, or of evaporation and deflagration, 

 which are sometimes had recourse to in order to separate the ar- 

 senic from the organic substances with which it may have been 

 mixed. 



I had the satisfaction of finding, on trial, that my anticipa- 

 tions were reaHzed ; and that I was thus able, not only to sepa- 



• The Large Gold Medal of the Societj of Arts of London, was presented 

 to Mr Marsh for the above valuable communication, which will appear in the 

 51st vol. of the Society's Transactions. 



