UNDTJLATORY FORCES. ELECTRO-METALLURGY. [WKKT SOLUTION*, rm. 



been mod a long time for silvering object* containing 

 cuj'jHT. In thin precipitation by hydrochloric acid, there 

 in hydrocyanic acid gas set free, therefore the operation 

 bhould only ho performed in the open air, or in a place 

 whore there is good ventilation. If the precipitate be 

 very rod, it must bo troatod with hot hydrochloric acid, 

 which will dissolve the cyanide of copper. The chloride 

 of silver having been washed with water, muit bo dried, 

 fused with potash in a Hessian crucible, and then coated 

 with borax, in the ordinary manner for obtaining metallic 

 silver. 



330. "This method is very simple in its application, 

 and Tery oconomicol, considering that, by the aid of the 

 hydrochloric acid, all the silver contained in the solution 

 of cyanide of potassium is precipitated, and there remains 

 no trace of it in the liquid. But the largo quantity of 

 hydrocyanic acid gas which is disengaged, is a circum- 

 stance which must be taken into serious consideration 

 when operating on large quantities of silver solution, the 

 vapour of which is most deleterious ; and nothing but the 

 most perfect ventilation, combined with arrangements 

 for the escape of the poisonous gases, will admit of the 

 process being carried on without danger to the work- 

 men: when, however, we have taken the precautions 

 dictated by prudence, the method in question may be 

 considered as perfectly practical. The liquid should be 

 poured into very capacious vessels, because the addition 

 of the acid produces a large amount of vapour. 



237. "Extinction of Silver by the Dry Method. The 

 solution of cyanide of silver and potassium is evaporated 

 to drynesK, the residue fused at a red heat, and the 

 resulting mass, when cold, is washed with water. The 

 r. maimier is the silver in a porous metallic condition. 

 There 'still remains in the wash-waters a little silver, 

 which may be precipitated by the addition of hydrochloric 

 acid. 



238. "Extraction of Gold by the Wet Method. A. 

 solution of gold and cyanide of potassium, which has 

 long served for gilding articles of silver alloyed with 

 copper, may still contain, as we have already remarked, 

 independently of the gold, both silver and copper, ana 

 perhaps iron. In order to obtain these metals we operate 

 in the following manner : 



"The liquid, the same as with the solution of silver, is 

 acidulated with hydrochloric acid ; in which cose there is 

 produced hydrocyanic acid gas, which requires the same 

 careful ventilation. Tliis addition of hydrochloric acid 

 causes a precipitate, which may, according to circum- 

 stances, consist of cyanide of gold, cyanide of copper, 

 and chloride of silver. The precipitate, washed and 

 dried, is boiled in aqua regia, which dissolves the gold 

 and copper in the form of metallic chlorides, and leaves 

 the chloride of silver unaffected. The solution, containing 

 the gold and the copper, is evaporated nearly to dryness, 

 in order to drive off any excess of acid ; it is then dis- 

 solved in a small quantity of water, and the gold pre- 

 cipitated from it by the addition of protosulnhato of 

 iron, in the state of a brown powder. The chloride of 

 silver is reduced to the metallic state by the usual means. 

 The liquid from which wo have precipitated the cyanide 

 of gold, etc., by hydrochloric acid, may yet contain a little 

 gold in solution. I refer to section 232 for its further 

 treatment 



239. "This method is distinguished by the great sim- 

 plicity of the operation, and wo may repeat for it all that 

 we have already said respecting the extraction of silver 

 by the wet method. 



240. "Extraction of Gold by the Dry Method. The 

 solution of cyanide of potassium, which contains gold, 

 silver, and copper, is evaporated to dryness ; the residue 

 fused at a red heat, cooled and washed (the wash-waters 

 still containing a little gold and silver; and this occurs 

 most often when the solution of either metal contains a 

 very huge excess of cyanide of potassium). Tho residue, 

 after washing, consists of gold and silver in a metallic 

 porous state, and carbide of copper resulting from tlie 

 decomposition of cyanide of copper by the heat. Tho 

 metallic residue is treated by aqua rogia. which forms 

 insoluble chloride of silver, and contains the chlorides of 



gold and copper in solution. In order to obtain these 

 metals in tho metallic state, we must proceed in the 

 manner previously indicated. 



241. " If we operate according to the method of Pro- 

 fossor Boettger, t.e., if we fuse the dried residue with its 

 own volume of litharge, in a covered crucible, the regulus 

 we obtain in this case consists of gold, rilvcr, and ' 



In treating this alloy by nitric acid of specific gravity 1 -, 

 and applying heat, tho gold remains in the form of a 

 brown powder, whilst the lead and tho silver are dissoh , ! 

 in tho acid. This solution, after having been diluted 

 with distilled water, may have tho silver separated from 

 the lead, by tho addition of hydrochloric acid. 



242. " These methods of extracting the silver and gold 

 from old solutions of cyanide of potassium by the dry 

 process, present this advantage, that tho operator is not 

 incommoded, while working, by the disengagement of 

 vapours of hydrocyanic acid. In those operations the 

 poisonous gases are not developed as they ore in the 

 process for extracting tho metals by tho wet process. 



243. " After the experiments hero reported, those who 

 are interested in the subject may choose for them 

 which of these methods appears the most suitable to the 

 circumstances in which they are placed, and tho object 

 which they wish to attain. 



244. "Means of Recovering Gold or Silver ly M. 

 Bottey. Cyanide of gold dissolved in on excess of cyanide 

 of potassium, resists all the means which we have tried 

 to separate them; and hydrosulphuric acid, for example, 

 does not produce a precipitate. By tho wet way we 

 cannot always precipitate the gold completely, and for 

 that reason MM. Ikettger, Hessenberg, Eisner, ;md 

 others, propose to evaporate the liquid to dryness; mix 

 the residue with its own weight of litharge; fuse the 

 mixture at a strong red heat ; then dissolve the lead from 

 the alloy by boiling it a long time with dilute nitric acid, 

 which leaves the gold in tho form of a h'ght sponge. 



243. "M. Wimmcr has more recently proposed to 

 evaporate the solution to dryness in a water bath, then 

 mix tho residue with one-and-a-half times its weight of 

 saltpetre, and introduce the mixture by small portions ;-t 

 a timo into a Hessian crucible, heated to redness in 

 order to cause explosions ; and to continue this until the 

 entire mass is in a state of quiet fusion. 



"Hi. "The first of these two processes does not give 

 room for any objection, except the employment of a : 

 heat, and the use of nitric acid ; the second process i 

 the contrary, disagreeable, and very uncertain. \\ . 

 know that saltpetre never explodes with moiv 

 than with cyanide of potassium ; and, notwithstanding 

 that tho inventor of the process advises us not to odd 

 more than small portions of the mixture at a time, tin: 

 explosions ore so powerful that they cannot bo caused 

 without loss of materials. 



247. " The following process is applicable, on the small 

 scale, with a spirit-lamp and a crucible of platina : 

 Evaporate tho solution to dryness ; mix the saline moss 

 with its own weight of sal-ammoniac, and heat it gently : 

 ammoniacal salts decompose, as wo have said, tho 

 metallic cyanides, and form cyanide of ammonium, which 

 is itself decomposed by the heat and volatilised, whilst tho 

 acid of the ammoniacal salt (tho body which salilies tho 

 ammonia) combines with tho metals (passed to the 



of oxides), which wore previously united to the 

 The sal-ammoniac, then, in this case forms chloride of 

 potassium and chloride of gold, and, if tho salt contain 

 ferro-cyonide of potassium, chloride of iron in addition. 

 The chloride of gold is easily decomposed ; the chloride 

 of iron is portly decomposed, and leaves oxide of iron in 

 beautiful crystalline spangles. The undocomposod portii >n 

 of tho chloride of iron, like tho chloride of potassium, 

 may, after tho decomposition is finished (which only 

 requires a low rod heat), be washed away with water, 

 leaving tho gold in tho form of a light coherent moss, 

 and tho iron in small spangles, which may be removed by 

 mechanical means. 



248. "If wo fear that a little of the gold remains 

 mixed with tho iron in .1 pulverulent state, wo may dis- 

 solve it in hot aqua rcgia, and precipitate the gold from 



