284 Means of detectitig Arsenic in the Animal Body, S^c. 



one should see them. It is volatile by heat, and is dissolved by 

 cold nitric acid, which solution gives to the nitrate of silver a 

 brick-red precipitate, the arsenate of silver. 



The antimonial tache is less metallic than the former in its ap- 

 pearance, also blacker, and when very dense even smutty. It 

 can be volatilized, but with great difficulty, and not before it has 

 been as it were chased about the surface of the porcelain. It is 

 soluble in cold nitric acid, which solution gives no red precipitate 

 with nitric acid. 



The next tacjie to be spoken of, is the compound one, of arse- 

 nic and antimony ; at the same time mention will be made of 

 the method adopted by M. Orfila for detecting the one or the other 

 of these metals in it. It partakes, as might be expected, of the 

 characters of both the metals that enter into its composition, being 

 partially volatile, soluble in nitric acid, from which the brick-red 

 precipitate of arsenate of silver can be obtained. M. Orfila pro- 

 poses a plan of separating the constituents of this tache, and of 

 testing each by itself He proceeds as follows: having collected 

 a number of the compound taches upon a porcelain plate, he dis- 

 solves them in nitric acid, which solution being poured into a 

 capsule, is evaporated to dryness, and a residue remains composed 

 of antimonious acid and a mixture of arsenic and arsenious acids. 

 Upon this residue a little water is poured, and the capsule slightly 

 heated, which enables the water to dissolve more readily the two 

 last mentioned acids. The antimonious acid being allowed to 

 settle, the clear liquid is decanted, and a few drops of nitrate of 

 silver being thrown upon it, the brick-red arsenate of silver is 

 formed, which is sometimes mixed with a considerable quantity 

 of a yellow precipitate, the arsenite of silver. This will, how- 

 ever, rarely happen, if a large quantity of nitric acid has been 

 used ; for by so doing, only an extremely small quantity can re- 

 main in the state of arsenious acid, the oxidation being carried a 

 degree higher. Nevertheless, if the entire precipitate produced 

 by the nitrate of silver be yellow, it can have no effect in de- 

 stroying the fact concerning the presence of arsenic, as it only indi- 

 cates that it has met with arsenious and not arsenic acid. But 

 to return to the substance left in the capsule : — A small quantity 

 of muriatic acid, slightly diluted, is poured upon it, which imme- 

 diately dissolves it. A current of sulphuretted hydrogen is now 

 made to pass through this solution, when the orange-colored sul- 



