Mr. Marsh on distitiguishi?ig Arsenicfrom Antimony. 283 



Thompson,"and which was inserted in the L. and E. Philosophi- 

 cal Magazine, vol. x. p. 353, has rendered the process in some 

 measure more difficult than was at first supposed, by the dis- 

 covery of that gentleman, of a compound in which antimony 

 combines with hydrogen to form a gas (antimoniuretted hydro- 

 gen). This gas gives off' by the process employed, metallic 

 crusts, which much resemble, to the inexperienced eye, the 

 metallic substance obtained from arsenical solutions by the 

 same arrangements. It becomes necessary therefore to find a 

 means of distinguishing these metallic crusts from each other. 

 Many processes which are well known to the experienced 

 chemist may be employed for this purpose ; but the misfortune 

 is that all these arrangements suppose a previous chemical 

 acquaintance with the subject; for instance, a good process for 

 this purpose is given by Liebig and Mohr in their valuable 

 Journal (Lieb., Ann., xxiii. 217.) and also a modification of 

 the same by Berzelius may be seen copied in the Lancet, 

 vol. i. 1838, p. 819, but these are all liable to the above ob- 

 jection, viz. want of simplicity. 



I am happy in being able to lay before your readers a very 

 simple distinguishing test for these bodies, and which I have 

 employed in all cases of doubt with perfect success. The 

 means that I use is simply as follows: After the common ar- 

 rangements have been made for testing for antimony or ar- 

 senic, the piece of glass or porcelain on which the metallic 

 crusts are generally received ; is to have a single drop of di- 

 stilled water placed on it; the glass or porcelain is then to be 

 inverted, so that the drop of water is suspended undermost. 

 The gas as it issues from the jet is to be inflamed in the usual 

 manner, but the piece of glass, &c., with its drop of water, is to 

 be held about an inch above the jet, or just above the apex of 

 the cone of flame : the arsenic by this arrangement is oxidized 

 at the same time that hydrogen is undergoing combustion, and 

 coming in contact with the drop of water held above, forms 

 with it a strong or weak solution of arsenical acid, according 

 to the quantity of arsenic present, should that substance have 

 been in the mixture submitted to examination. A very minute 

 drop of Hume's test (the ammoniacal nitrate of silver) being 

 now dropped on the solution so obtained, if arsenic be present, 

 the well-known characteristic lemon yellow colour produced 

 by this test when used for testing for that substance is imme- 

 diately produced, namely, the insoluble arsenite of oxide of 

 silver. Antimony under these circumstances, from being in- 

 soluble, produces no change. I have found it useful, when 

 much arsenic has been present in the matter submitted to ex- 

 amination, to use a clean glass tube, 6 inches long, and about 



