124 



ESSAY VI. 



till the retort melted. The platina lay at the bottom in the 

 fused acid ; a little arsenic was sublimed. After it was cool, 

 I poured some water into the retort, which dissolved the acid. 

 This acid was rendered opaque by a white powder, which 

 was afterwards lixiviated with water, and then dried. It 

 grew black upon charcoal before the blowpipe, had a smell 

 like arsenic, and was attracted by the loadstone. The 

 platina, after it was dried, had hardly lost anything of its 

 weight. Pure platina, consequently, is not attacked by the 

 acid of arsenic. (&) The solution of platina in aqua regia 

 is not precipitated by the acid of arsenic, but readily by the 

 arsenical neutral salts. The precipitate in this case is 

 yellow; it is soluble in a large quantity of water; but it 

 contains no mark of acid of arsenic. A mixture of acid of 

 arsenic and muriatic acid has no effect upon platina, neither 

 has a mixture of nitrous acid and the acid of arsenic. 



SECTION XXIV. UPON SILVEK. 



(a) Pure silver is not attacked by the acid of arsenic in 

 digestion. After the whole of the liquid was abstracted, I 

 increased the fire till the acid came into fusion. Here more 

 arsenic was sublimed than in the foregoing experiments with 

 gold and platina. This degree of heat being continued for 

 half an hour, the silver dissolved. After the retort was 

 grown cold, I broke it, and found that it contained a 

 colourless glassy mass, nearly transparent. The retort was 

 covered with a glazing of a flame-colour, which could not 

 be separated from the glass by any solvent, (b) Upon the 

 vitreous mass, after it was pounded, I poured some distilled 

 water, and exposed it to a sand - heat, upon which it 

 immediately lost its transparency, and assumed a brown- 

 red colour ; the acid of arsenic was dissolved, and a brown 



