78 HYDROMETALLURGY. [III. 



The gilding is begun in a solution containing 0.1 gm. gold in 

 1 decilitre of liquid, and finished in a solution not yet ex- 

 hausted, whereby the beauty of the gilding is heightened. 

 AVhen the solutions have been too dilute, they are evaporated 

 in an iron kettle to dryness, the residue fused in a crucible, 

 and the salts washed out from the metallic gold. Coke-iron 

 batteries are employed, and the electric current so regulated, 

 that an evolution of gas may be perceptible at the anode, but 

 not on the gilding surface. In the latter case, the current is 

 diminished by removing some of the cells, by lessening the 

 surface of the anode, or increasing that of the cathode (gilding 

 surface). 



Eisner justly remarks, on Leuchtenberg's method of analyz- 

 ing the solutions to determine the quantity of gold or silver 

 precipitated, that the practical gilder could not execute a fine 

 assay of this kind, and that the simple method of weighing 

 the gold or silver anode before and after use will give a suffi- 

 ciently close determination of the amount of gold expended. 



Matt Grilding and Silvering. — According to R. Bdttger, a 

 matt silvering is always obtained in a boiling solution of 

 washed chloride of silver, dissolved in cyanide of potassium, 

 by a moderate and constant electric current. A matt gilding 

 is obtained in a boiling solution of ammonia-oxide of gold 

 dissolved in cyanide of potassium, to which a small quantity 

 of potassa has been added. The gilding is still finer when 

 the articles have been previously matt-silvered. (Polytech. 

 Notizbl. by R. Bottger, 1846.) See also Eisner's experiments 

 on matt gilding with yellow prussiate of potash, in Verb. d. 

 Gewerbfleisses f. Preussen, 1843. 



Crold and Silver recovered from exhausted Cyanide Solu- 

 tions. — To recover gold and silver from solutions of cyanide 

 of potassium or yellow prussiate of potash, the solutions are 

 evaporated to dryness, heated to redness, and extracted with 

 water, when the metallic gold or silver will remain. Another 

 method is pursued with a potassa solution of the prussiate. 

 A silver solution is heated with muriatic acid under a draft 

 (to carry off prussic acid), and the precipitated chloride well 



