ON ARSENIC 125 



powder remained at the bottom. The acid contained a little 

 of the silver in solution ; for, on adding muriatic acid, some 

 luna cornua was precipitated, (c) The brown powder was 

 dried, and exposed to such a degree of heat that the retort 

 melted. The powder entered into fusion, but no arsenic 

 was sublimed. When the retort was cooled, I broke it, and, 

 upon taking the mass out, I found it transparent at the 

 margin. (d) As calx of silver is reducible without the 

 addition of phlogiston, as is likewise the case with acid of 

 arsenic (Sec. v. (&)), I tried what a greater degree of heat 

 would effect. I therefore put the glassy mass into a 

 crucible, over which I luted another, and afterwards applied 

 as strong a heat as silver requires for being melted. After 

 the apparatus was cooled, the silver was found reduced, and 

 surrounded with a little white glass. (e) The solution of 

 silver is precipitated by acid of arsenic, but not entirely ; 

 the precipitate is of a brown colour. More is precipitated 

 by the neutral arsenical salt of Mr. Macquer ; but as this 

 salt is supersaturated with acid, some silver is retained in 

 the solution. The neutral arsenical salts (Sees. vi. (a), vn. 

 (a), vni. (a)) decompose the solution entirely. (/) If this 

 precipitate of silver be digested in muriatic acid, the acid 

 of arsenic is expelled, and it is changed into muriated silver. 

 In the same manner this brown precipitate is soluble in 

 spirit of sal ammoniac* prepared with lime. (g) Though 

 neither the acid of arsenic nor the muriatic acid alone 

 attack silver, a mixture of them has considerable action 

 upon this metal. If the solution of silver in nitrous acid 

 be precipitated by copper, and the precipitate well washed 

 with hot water, and afterwards digested for fourteen days 

 in a close vessel, with two parts of acid of arsenic, and two 

 parts of muriatic acid, the silver is changed into a white 

 powder, which, after being edulcorated and dried, is found 



