TEST FOR ARSENIC. 177 



there are such easy and obvious means by which this ambi- 

 guity can be entirely removed, that it can make no solid ob- 

 jection to the utility of the test. 



There cannot be the le art doubt, as Mr. S. observes, but Remedy. To 



• • "will rill OX.C(*SS 



that whenever nitrate of silver is added to a solution containing of ni , rate f 

 muria'i;: acid, a precipitate of muriate of silver must be the silver; which 

 consequence. But if the nitrate of silver be added in excess, J[ w „ '^ ar- 

 the arsenite of silver is also thrown down by the intervention seme, 

 of ammonia, and a mixed precipitate of luna cornea and arse- 

 nite of silver is obtained, which partakes more or less of the 

 yellow colour of the latter, according to the proportion of the 

 two salts. 



If to this dubious precipitate a few drops of dilute nitric and the arse- 

 acid be added, the arsenite of silver is instantly dissolved, and ™* e . £ e **kuo 

 the muriate of silver, which is insoluble, immediately resumes up by ail. ni- 



its peculiar density and whiteness. If a little ammonia be now ?" c acld ' and 



r } then precip. 



added to the clear fluid, the yellow precipitate appeal s in the yellow by am* 



most distinct manner, and becomes even more characteristic monia « 



from a comparison with the white precipitate, the appearance 



of which differs from this in every respect. 



By this method, I believe that every objection to the test 

 will be removed ; and in order to anticipate all ambiguity, and 

 to avoid any complication or practical difficulty in its applica- 

 tion, I would propose to modify the process in the following 

 manner : 



To the suspected fluid, previously filtered, add, first, a little Easy manipu- 

 dilute nitric acid, and, afterwards, nitrate of silver, till it shall las^proces*!!" 

 cease to produce any precipitate. The muriatic acid being 

 thus removed, whilst the arsenious acid (if any, and in what- 

 ever state,) remains in the fluid, the addition of ammonia will 

 instantly produce the yellow precipitate in its characteristic 

 form. It is hardly necessary to add, that the quantity of am- 

 monia must be sufficient to saturate any excess of nitric acid 

 which the solution may contain. 



