1824.] Dr. Traill on the Detection of Arsenic. 131 



and you almost congratulate yourself upon the errors committed 

 with respect to sulphuric acid, as better adapted for your pur- 

 pose than the truth would have been ; what happy advantage 

 you may discover in the utter confusion in which you have in- 

 volved the Berzelian symbols, I cannot imagine ; and although 

 your student may, in the commencement of his career, acquire 

 scepticism or iudifforence in theoretical points, he must, I think, 

 terminate it in the belief that you do not possess " that cautious 

 habit of distinction " which it is your boast to have attained. 



Yours, &.c. R. Phillips. 



Article XV. 



Ou the Detection of small Quantities of Arsenic. 

 By T. S. Traill, MB. &c. 



(To the Editor of the Annals of Philosophy.) 



DEAR SIR, Liverpool Royal Institution, Jan. 16, 1824. 



Youu very interesting paper in the last number of the Annals, 

 on the tests of arsenic, followed by an application to examine the 

 contents of a stomach in which I discovered that deleterious 

 substance, has drawn my thoughts to a subject which has often 

 engaged my attention, from having been repeatedly called on to 

 determine the nature of substances found in the alimentary canal 

 of persons who have died under suspicious circumstances. 



Your remarks on the application of the usual liquid tests are 

 extremely just, and, in my opinion, leave nothing further to be 

 desired on the subject ; but 1 have long been aware of the erro- 

 neous opinion entertained by authors of reputation, respecting 

 the inutility of attempting to reduce to the metallic state, portions 

 of white arsenic considerably less than a grain. Even by the 

 common process, 1 have often succeeded in reducing to a per- 

 fect metallic film much less than half a grain of the arsenious 

 acid ; although it was the opinion of the celebrated Black, that 

 one grain", and of Dr. Bostock that three-quarters of a grain, are 

 the smallest quantities from which we can hope distinct results 

 by this process. 1 may here notice the importance of attempt- 

 ing the reduction in all cases of suspected poison; for it has 

 several times happened, that I have been able to show the pre- 

 sence of arsenic in cases where it has been supposed absent, 

 because the white powder gave no alliaceous smell when thrown 

 on a live coal. This method of operating should be abandoned ; 

 because the carbonic acid and sulphureous vapour from the coal 

 disguise the peculiar odour of the arsenic; and much of the 

 powder is probably raised in vapour without reduction, and con- 

 sequently without giving out the alliaceous smell. 



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