128 PROCESS OF ELECTRO-GILDING. 



siderable loss to the cyanide of potassium. There is always formed in 

 this deposition a quantity of ammonia and carbonic acid, from the 

 deposition of the cyanate of potash ; and if the chloride of gold be 

 recently prepared and hot, there is often formed some aurate of 

 ammonia (fulminate of gold), which precipitates with the cyanide of 

 gold. Were this precipitate to be collected and dried, it would ex- 

 plode when slightly heated. On previously diluting the chloride of 

 gold, or using it cold, this compound is not formed. 



After the free acid is neutralized by the potash, further addition 

 of the cyanide of potassium precipitates the gold as cyanide of gold, 

 having a light yellow colour ; but as this is slightly soluble in am- 

 monia and some of the alkaline salts, it is not advisable to wash the 

 precipitate, lest there be a loss of gold: cyanide of potassium is 

 generally added until the precipitate is redissolved; consequently 

 much impurity is formed in the solution, namely, nitrate and 

 carbonate of potash with chloride of potassium and ammonia. 

 Notwithstanding, this solution works very well for a short time, 

 and it is very good for operations on a small scale. 



Battery Process of Preparing Gold Solution. The best method of 



preparing the gold solution is that described for silver (p. 107). Say 

 the operator wishes to prepare a gallon of gold solution, he dissolves 

 four ounces of cyanide of potassium in one gallon of water, and heats 

 the solution to 150 Fah., he now takes a small porous cell, fill it with 

 this cyanide solution, and place it inside the gallon of solution : into 

 this cell is put a small plate of iron or copper, and attached by a 

 wire to the zinc of a battery. A piece of gold is placed into the 

 large solution, facing the plate in the porous cell, and attached to the 

 copper of the battery ; the whole is allowed to remain in action until 

 the gold, which is to be taken out from time to time and weighed, 

 has lost the quantity required in solution. By this means a solution 

 of any strength can be made, according to the time allowed. The 

 solution in the porous cell, except the action has continued long, will 

 have no gold, and may be thrown away. Half-an-hour will suffice 

 for a small quantity of solution ; of course any quantity of solution 

 may be made up by the same means. For all the operations 

 of gilding by the cyanide solution, it must be heated to at least 130 

 Fah. The articles to be gilt are cleaned in the way described for 

 silver, but are not dipped into nitric acid previously to being put in 

 the gold solution. Three or four minutes is sufficient time to gild 

 any small article. After the articles are cleaned and dried, they 

 are weighed ; and, when gilt, they are weighed again : thus the 

 quantity of gold deposited is ascertained. Any convenient means 

 may be adopted for heating the solution. The one generally adopted 

 is, to put a stoneware pan containing the solution into a vessel of 

 water, which is kept at the boiling point. The hotter the ^solution, 



