544 



HISTOUt or ftOLB. 



Changed to 

 purple of Cas- 



Fulminating gold moistened with muriate of tin changes t» 

 the purple powder of Cassius, because it parts with oxigen ; but 

 the purple powder thrown into ammonia gives very different re- 

 sults, as we shall see further on. 



Gold and Mercury. 



Muriate of goia On letting fall a solution of gold, drop by drop, into a solu-^ 

 with nitrate uf . „ . ° r ^ r' 



mercury at a "°" °* nitrate of mercury at a minimum, a violet powder is 

 minimum. thrown down, which, according to Orschal, yields a very fine 

 purple. This purple is a mixture of metallic gold and sweet 

 muriate, which may be separated from each other by merely 

 heating them in a retort. Qn the contrary, if the solution of 

 mercury be poured into that of gold, so that the latter predo- 

 minates, the precipitate will be found after the space of twelve 

 hours to be pure gold. This arises from the mercurius dulcis 

 - being decomposed in its turn. In fact, if mercurius dulcis be 

 kept in a purely muriatic solution of gold, it precipitates the 

 ^ gold, disappears, and is found to be converted into corrosive 



sublimate. 



With nitia'e at Nitrate of mercury, the oxide of which is completely at the 

 • maxiauim, ii • • - , c j 



ir; tnum, likewise precipitates the muriate of gold, but the 



rv:;ii'ts are very different, and deserve to be made known. 



To understand all that passes in this precipitation, it must 

 be remembered, 



1st.— ^Thatthe oxide of mercury being more powerfully at- 

 tracted by the muriatic acid than by the nitric, it has always a 

 tendency to quit the latter, in order to unite with the former, 



2^d. — That the oxide of mercury having a stronger affinity 

 than that of gold for the muriatic acid, the former ought infal- 

 Jibly to displace the latter from this acid. 



3d. — That, if the mercury be once saturated with oxigen, it 

 will precipitate the gold with all its oxigen ; that is, as it exists 

 in the solution, because in this case it has no motive to take it 

 from the gold. 



■^th. — That, if the oxide of gold be separated from the muri- 

 atic acid by that of mercury, it will fall down, from being inso- 

 luble in the uitric acid, which the oxide of mercury has 

 quitted. 



These four effects actually take place in the precipitatioa 

 about to be mentioned. 



A solu- 



