Polytechnic Association Proceedings. 931 



Protochloride of gold Au C: Yellowish white, formed by heating 

 terchloride of gold to the melting point of tin, in a porcelain 

 basin. Hydrogen gas, passed for some time through a neutral 

 solution of chloride of gold, gives a fine purple red color, without 

 forming a precipitate. 



Terchloride of gold Au CP. Gold leaf heated in chlorine gas 

 absorbs it w^ithout visible combustion. Gold leaves and finely 

 divided gold, obtained by precipitation, dissolves in heated hydro- 

 chloric acid. Gold dissolves, even at ordinary temperatures, in 

 chlorine water, in mixture of nitric acid with hydrochloric acid, 

 sal ammoniac, and common salt, and in mixtures of hydrochloric 

 acid with nitrates, or with chromic acid. 



Au+N 0^+3 H Cl=Au Cl'+3 H O+N 0'. 



It is very interesting to study the action of the various metals 

 and other elements, as well as compounds on the solutions of ter- 

 chloride of gold. Some precipitate the gold as yellow metallic 

 gold, some as a black powder, and some as the red oxide. In 

 short, there is evidently a large field for research. 



I extract the following curious item from Gmelin's Handbook of 

 Chemistry: 



" Gold and silicium: Finely divided metallic gold, chloride of 

 gold, fulminating gold, the precipitate thrown down from solution 

 of the chloride by potash, or by silicate of potassa, the purple of 

 cassias, etc., fused at a continued gentle heat, with a glass contain- 

 ing oxide of lead, impart to it, according to circumstances, a yellow 

 or purple red color. Among the various explanations which have 

 been suggested for the red coloring which has been imparted by 

 heat to colorless auriferous glass, the most probable, according to 

 H. Rose {Pogg 72, 556), is that the colorless glass contains a silicate 

 of aurous oxide, which requires a high temperature to produce it, 

 and can bear that temperature without decomposition; but that 

 when it is heated to a lower temperature, part of the aurous oxide 

 separates out, and produces the color, and finally, at a stronger 

 heat, the separate aurous oxide is reduced, and the glass thereby 

 rendered liver-colored and opaque." 



It would take us too long were we to review even the most 

 important combinations of gold with other substances; enough, 

 however, can be seen from this, that there must exist similar com- 

 binations in nature; we have only to look for them, and specially 

 among the silicates, the combinations of gold with metalloids and 



