ON ARSENIC 119 



equal parts. Of these one was mixed with charcoal powder, 

 and distilled with a strong fire; but neither arsenic nor 

 regulus was sublimed. Whence it appears that I took too 

 small a quantity of acid of arsenic to decompose this fluor, 

 which contained a small quantity of pyrites (Sec. v. (c)). The 

 other half was mixed with four parts of acid of arsenic, and 

 the mixture was distilled. When the mass grew dry, a 

 little yellow sal ammoniac was sublimed, whereupon the 

 water in the receiver was covered with a white crust. I 

 frequently shook the receiver, in order to make this crust 

 fall to the bottom, and continued the distillation as long as 

 any crust formed upon the water. This crust was siliceous 

 earth, and the water contained acid of fluor. 



SECTION XV. EFFECTS OF THE ACID OF ARSENIC UPON EARTHS. 



LIME. 



(a) When acid of arsenic is dropped into lime-water, the 

 lime precipitates, in combination with the acid of arsenic. 

 If more acid be dropped in, the precipitate is again dissolved. 

 If the solution be evaporated, small crystals shoot. If these 

 be dissolved in a little water, and some vitriolic acid dropped 

 into the solution, a precipitation of vitriolated lime takes place. 

 (6) If the acid of arsenic be diluted with water, and some 

 powdered chalk added, it will at first dissolve ; but, on 

 adding more chalk, the whole solution will coagulate into 

 small crystals, (c) The acid of arsenic does not precipitate 

 the solutions of nitrated, muriated, and acetated lime ; 

 neither are these solutions precipitated by the neutral 

 arsenical salt of Mr. Macquer ; but the arsenical salts 

 (Sees. vi. (a), vn. (a), vui. (-)) decompose these solutions, and 

 form a precipitate which is not soluble in water, though it 

 is of easy solubility in acids. (d) If the precipitate of 



