62 Messrs. Glassford and Napier on the 



heat with carbonate of potash, it is entirely decomposed, and 

 the gold may be obtained in a bright metallic button. 



11. The cyanide obtained by the decomposition of the double 

 salt by acids was examined in this way and the following re- 

 sults obtained : — 



10 grs. yielded 8*82 grs. of gold = 88*20 per cent. 

 15grs. ... 13-23 grs. ... =88*20 ... 

 7 grs. ... 6-17 grs. ... =88*14 



These results approximate so very closely to the calculated 

 result, viz. 88*30 per cent., that we are at once led to the con- 

 clusion that it is a true proto-cyanide, the constitution of 

 which is represented by Au + Cy. 



A cyanide of the constitution represented by Berzelius and 

 Kane would contain only 71*56 per cent. 



The cyanide of gold obtained by the first process is gene- 

 rally contaminated, as already mentioned, with silica and a 

 small portion of iron, obtained from the cyanide of potassium 

 employed : these impurities will vary according to the state 

 of the cyanide used. Before these facts were ascertained the 

 analyses of the cyanide of gold yielded the following very 

 variable results, — 85*00 per cent., 85*50 per cent., 85*57 

 per cent.; this last sample, when thoroughly washed with 

 water, carefully dried and examined, gave still only 86*00 per 

 cent. 



12. Cyanide of Gold and Potassium. — This salt, which is 

 that now so extensively employed in gilding by the electric 

 force, may be obtained by various processes: — 1. By dissolving 

 the cyanide of gold, prepared by the first process just given, 

 in cyanide of potassium. 2. By dissolving oxide of gold in 

 cyanide of potassium. The oxide of gold is prepared for this 

 purpose by digesting calcined magnesia in nitro-muriate of 

 gold, as is well known ; as it is very apt to retain a portion of 

 magnesia as usually prepared, it is better to boil the oxide so 

 obtained in strong nitric acid, to filter through close muslin or 

 calico, allowing the green nitrate solution to fall into a large 

 quantity of distilled water. The oxide of gold is thus ob- 

 tained quite pure, and as a very bulky reddish-brown pre- 

 cipitate, which when dried contracts, and becomes of a pale 

 brownish-yellow colour: it dissolves readily in cyanide of po- 

 tassium, with the assistance of a little heat, or by digestion, 

 and constitutes the salt in question. 3. It may also be ob- 

 tained, as already mentioned, by adding a solution of cyanide 

 of potassium to terchloride of gold until the solution becomes 

 colourless. As the reactions which take place with these so- 

 lutions are exceedingly interesting, and calculated to add evi- 

 dence to the existence of a hitherto unobserved law, which 

 will be fully brought out when treating of the double silver 



