OOLD SOLDTIONS.] 



UNDULATORY FORCES. ELECTRO-METALLURGY. 



227 



about four ounces of the mixture, and when crystallised 

 into the red mass, will weigh about one ounce aud 

 1G5 grains. 



152. Cyanide of Gold. "Cyanide of gold is formed 

 by cautiously adding a solution of cyanide of potassium 

 in six parts of water, to a normal solution (i.e., not 

 containing any free acids) of terchloride of gold, con- 

 sisting of one part of the chloride and five parts of water, 

 until a copious yellow precipitate settles down ; if more 

 cyanide of potassium be added, the precipitate becomes 

 dirty yellow, and is more quickly deposited; a still 

 larger quantity renders it orange yellow. It is a crystal- 

 line powder, permanent in the air. By ignition it is 

 resolved into gold and cyanogen gas ; it is not decomposed 

 by sulphuric, hydrocliloric, or nitric acids, nor by aqua 

 regia, unless freshly precipitated, and then only slowly. 

 It is not decomposed by sulphuretted hydrogen ; hydro- 

 sulphate of ammonia dissolves it slowly but completely, 

 forming a colourless solution, from which, by the addition 

 of acids, sulphide of gold is precipitated. It dissolves in 

 aqueous solutions of ammonia, hyposulphite of soda, or 

 alkaline cyanides ; but not in water, alcohol, or ether." 



153. " Gold precipitated from a solution of chloride 

 of gold by protosulphate of iron, dissolves in a boiling 

 solution of cyanide of potassium ; a hot solution of 

 cyanide of potassium will also dissolve ordinary metallic 

 gold if air be present. Both oxide of gold and aurate of 

 ammonia, dissolve completely in a solution of cyanide 

 of potassium, and form double cyanide of gold and 

 potassium. Cyanide of gold requires 23 parts of a 



a of cyanide of potassium in water to dissolve it. 

 ry one part of gold to bo dissolved by the battery 

 process, a solution of six parts of cyanide of potassium, 

 in from two to four times their quantity of water, at 

 100 Fah., is required; two electrodes of gold, con- 

 nected with a juitablo battery, are to be immersed in it 

 until the required quantity of gold is dissolved." " The 

 crystallised cyanide of gold and potassium dissolves in 

 seven parts of cold, and in half a part of hot water;* 

 in four parts of cold and in P 8 parts of hot water, t 

 It dissolves very sparingly in alcohol. Its aqueous 

 solution gilds copper ana silver by simple immersion, 

 especially if hot, and those metals are dissolved." 



151. finding by Immenion. The following solutions 

 have been used for gilding by the simple immersion, 

 or "water-gilding" process: First, dissolve five troy 

 ounces of grain gold in fifty-two avoirdupois ounces of 

 hot aqua regia, until vapours cease to bo evolved. 

 Decant the clear liquid when cool; dilute it with four 

 gallons'of distilled water ; add twenty pounds of purified 

 bicarbonate of potash, and boil it for two hours. The 

 articles to be gilt are immersed in the liquid from a fow 

 seconds to one minute, according to the kind of metal 

 immersed, and the temperature and newness of the 

 liquid; warmth assisting the action, and a new liquid 

 acting more quickly than an old one. Second : for 

 gilding silver articles, dissolve equal parts of bichloride 

 of mercury (corrosive sublimate) and sal-ammouiao in 

 nitric acid ; add pure gold to it, and evaporate the liquid 

 by heat to half its volume. Apply the liquid, while hot, 

 to the surface of the article. 



1 .").">. Joseph Steole's patent, dated August 9th, 1855. 

 Dissolve an ounce of gold in a mixture of four ounces of 

 hydrochloric acid and eight ounces of nitric acid, and 

 evaporate the solution to dryness. Fuse together 24 

 ounces of ferro-cyanide of potassium, and 12 ounces of 

 carbonate of potash : when this is nearly cold, dissolve 

 in two or three gallons of pure boiling-water ; cool and 

 filter the solution ; then add the chloride of gold, and 

 boil for a quarter of an hour. The articles to be coated 

 are connected with a piece of zinc, of suitable size, and 

 immersed in the liquid, the latter being at a temperature 

 of 80 or 85 Fall. 



I.V.. Quid Solution for Oie Battery Procets. For the 

 battery process there are many gold solutions, though 

 but fow good ones : 1st. The hyposulphite of gold and 

 soda formed by dissolving chi./vido of gold in a solu- 

 tion of hyposulphite of soda ; which is not considered 

 Ilimly. t Olmford ud Xapior. 



a good liquid for practical purposes. 2nd. The sulphite 

 of gold and potash, used by Mr. Woolrich : his solution 

 is made by adding sulphite of potash to water, saturating 

 five-sixths of the resulting liquid with oxide of gold, and 

 then adding the other portion of solution to form free 

 sulphite. 3rd. The terchloride of gold dissolved in watei 

 is a very inferior liquid for practical purposes, because 

 all the common metals decompose it. 4th. The bromide 

 of gold, proposed by Mr. Spencer, is made as follows : 

 "Make a mixture of equal parts of bromine aud alcohol ; 

 and of this mixture take one part, of acetic acid one part, 

 and four p.irts of water containing a few drops of sul 

 phuric acid. " The resulting liquid is then nearly saturated 

 with gold by suspending in it two electrodes of that 

 metal, and connecting them a sufficient time with a 

 suitable battery; when nearly saturated, add to the 

 solution three times its volume of water containing a few 

 drops of sulphuric acid. 



157. Electro-Gilding Liquid. The best liquid that has 

 yet been tried for practical electro-gilding, consists of the 

 double cyanide of gold and potassium dissolved in water. 

 It was first patented by Messrs. Elkiugton, and may be 

 formed, either by dissolving finely-divided gold, or any 

 salt of gold, in a solution of cyanide of potassium ; or by 

 the battery process, by suspending two electrodes of gold 

 in a solution of cyanide of potassium, and passing a 

 current from a small battery until the cathode receives a 

 proper deposit, the liquid being at about 100 or 150 Fah. 



158. Cyanide of Gold by Cfamiccd Process. The cyanide 

 of gold and potassium gilding solution is often made by 

 the chemical method as follows : Form some terchloride 

 of gold (151), and dissolve it in water ; then either add 

 a cold solution of caustic potash as long as a precipitate 

 is produced, filtering and washing the precipitate with 

 distilled water, or by digesting the chloride solution with 

 magnesia. Filter, and wash the precipitate first with 

 nitric acid, and then with distilled water ; or add to the 

 chloride liquid a solution of carbonate of ammonia, until 

 a precipitate ceases to be formed ; filter, and wash the 

 precipitate with water The precipitates produced by 

 potash or by magnesia, consist of oxide of gold ; whilst 

 those produced by ammonia, or its carbonate, are aurate 

 of ammonia (fulminate of gold), which is a very explosive 

 compound. The precipitate, after being well washed by 

 the successive additions of clean water, should be added, 

 whilst still wet, to a solution of cyanide of potassium, 

 containing the proportion of one pound of cyanide to one 

 gallon of water ; and then about one-fifth more of the 

 same solution should be added to form free cyamdo. A 

 very good proportion of the ingredients is, one ounce of 

 gold, one pound of cyanide of potassium, and one gallon 

 of water. The wash-waters should not bo thrown away 

 without being tested for gold, by immersing a piece of 

 bright zinc in them, and observing if it receive a yellow 

 deposit; in that case, a solution of protosulphato of 

 iron should be added as long as a precipitate of a greenish- 

 brown powder, which is metallic gold, is produced. If 

 this fail to precipitate the whole of the gold, a sheet of 

 bright zinc should bo immersed in the liquid, taken out 

 occasionally, and the deposit of gold brushed off by a 

 hard brush in wt.ter containing a little sulphuric acid. 

 The greater the quantity of free acid contained in the 

 original chloride solution, and the larger the excess of 

 potash, ammonia, or carbonate of ammonia added, the 

 greater is the amount of gold dissolved in the wash- 

 waters. If, when we dissolve the terchlorido of gold in 

 water, a yellow powder remain undissolvod at the bottom 

 of the vessel, it indicates that there is no free acid in the 

 salt; and it may bo redissolvcd by the addition of a 

 small quantity of the mixture of nitric and hydrochloric 

 acids, and the application of heat. 



159. Solution by Battery Process. The same solution 

 may bo made by the battery process, thus : Dissolve 

 some cyanide of potassium in hot distilled water, in the 

 proportion of from one to two pounds to the gallon ; 

 nearly fill a small porous cell with the liquid, :unl 

 immerse it nearly to its edge in the solution; place a 

 large gold anode in the outer liquid, and a small bright 

 copper cathode in the liquid of the porous ceil, and 



