Davy — On Arsenical Compoimds. 22?. 



XXXy. — Ojt a Eeadt Means of Detectii^g Assektcal Compoxtitds. 

 By EciruND W. Datt, A. M., M. D., Professor of Forensic Medi- 

 cine, Royal College of Surgeons, etc. 



[Eead June 14, 1875.] 



The extensive employment of certain compounds of the metal arsenic 

 for the criminal destruction of human life, has rendered their detection 

 under different circumstances a matter of great importance to society ; 

 and to attain tliis end they have long been objects of much interest to 

 the chemist and toxicologist. Fortunately for mankind, the metal 

 itseK, as weR as its combinations, have been found to be endowed with 

 very characteristic chemical properties, and on these are based several 

 excellent tests, by which, in the hands of the chemist or in those 

 skilled in the detection of poisons, very minute quantities of arsenic or 

 of its compounds can be identified with more or less facility ; and the 

 fear of such detection has acted as a great preventative against their 

 criminal employment as poisons ; for, before such means of recognising 

 their presence were discovered, secret poisoning by arsenious acid, 

 which is popularly known as "arsenic," was carried on to a fearful 

 extent, a greater number, perhaps, of indivduals having been already 

 deprived of life by that substance than by all the other known poisons 

 put together. But now, owing to our possessing the means by which 

 even very minute quantities of arsenical compounds can be detected 

 with almost unerring certainty, and there having been of late years 

 certain legal restrictions placed on the sale of arsenic, cases of homi- 

 cidal poisoning by that substance have now become comparatively rare. 

 Still, as such cases or those from accident do from time to time occur, 

 and as different arsenical compounds are usedfor a number of industrial 

 purposes, some of which are highly objectionable, endangering as they 

 do the health, and even lives, of many individuals, it is very desirable 

 that we should be able readily to detect those virulent substances, not 

 only where they may occur by design or accident in different articles 

 of food or drink, or in the bodies of those who have died from their 

 effects, but likewise where they may exist in various manufactured 

 products, the use of which might be attended with very serious conse- 

 quences. The test which I would now propose being one of such 

 simplicity and ease of execution that it might be performed by almost 

 anyone, will, I should hope, be found useful for the objects stated, 

 especially to those who are not very conversant with the details of 

 chemical manipulation. As it is a modification of Mr. Marsh's test, it 

 is necessary for me briefly to refer to that method before describiag the 

 one I would now suggest. That gentleman's test, as is well known, 

 is founded upon the circumstance, that nascent hydrogen in presence 

 of certain compounds of arsenic will give rise to the formation of 

 arseniuretted hydrogen ; a gas which, being possessed of very charac- 



K. I. A. PEOC, SER. 11., VOL. II., SCIENCE. 2 H 



