402 EECENT PEOGRESS IN PHYSICS. 



nitric acid is added, from time to time, until all the gold is dissolved;, 

 or ten to twelve times its weight of aqua regia may at once be taken ; 

 the solution is then evaporated to dryness. The chloride of gold thus 

 obtained is dissolved in water, and the yellow protechloride separated 

 by filtration ; carbonate of soda is then added until a feeble alkaline 

 reaction is observed, and at last the solution of cyanide of potassium 

 (one part of salt to ten to twenty of water) is stirred in. When all 

 is well dissolved, and the solution, which at first appeared turbid, is 

 again clear, it is boiled for half an hour. When the color of the. 

 gilding becomes impure, carbonate of soda is again to be added, and 

 the boiling repeated, or more cyanide of potassium may be used, 

 especially if the gold at the anode is no longer perfectly dissolved. — ■ 

 (Ryhiner, Dingler's Journal, vol. 110.) A fine red color is obtained 

 when the process is carried on at a moderately elevated temperature. 

 The silver solution consists of one part crystallized nitrate of silver in 

 thirty- two distilled water, to which solution of cyanide of potassium 

 is added until the precipitate which at first appears is again dis- 

 solved. — (Eisner, Dingler's Journal, vol. 88.) Freshly precipitated 

 and well washed chloride of silver is also used ; as much of this i& 

 stirred at intervals into a solution of one-tenth cyanide of potassium 

 in one of water as can be dissolved, and then as much more cyanide of 

 potassium and water is added. This solution may also be used for 

 electrotype silver work. For the copper solution, one part of sulphate 

 of copper in twelve of water are used, and the process conducted as 

 with the silver. But coppering does not succeed well with a single 

 pair ; a battery of at least two or three elements should be used. 



I omit here a number of suggestions in reference to the use of other 

 compounds, because they never came into practice, and I shall only 

 mention that the addition of a minute quantity of sulphuret of carbon 

 is especially favorable to the precipitation. — (Millward and Lyons, 

 Dingler's Journal, vol. 108, from the Repertory of Patent Inventions, 

 February, 1848.) Five ounces of sulphuret of carbon are mixed with, 

 six quarts of the gilding fluid, and of this mixture two ounces are 

 daily added to every ten quarts of the solution of metallic cyanide. 

 This is confirmed by Elkington, at least for silver. — (Dingler's 

 Journal, vol. 114, from the Practical Mechanic's Journal, October, 

 1849.) Peculiar difficulties occurred in the platinizing j^rocess as 

 well as in that of coating with nickel, and so far all the progress 

 made seems not to have rendered the processes practically applicable. 

 According to Fehling (Dingler's Journal, vol. 86) and Bottger (from 

 Annaden der Chemie und Pharraacie, September, 1843, vol. 90,) the 

 best results are obtained by adding a little ammonia to the chloride 

 of platinum and ammonia. Buttger also recommends a similar pro- 

 cess for nickel ; but the preparatory purification of the commercial 

 metal is very troublesome. 



In coating iron with zinc by means of galvanism (Pelatt, Dingler's 

 Journal, vol. 95, from Technologiste, February, 1845,) an acid solu- 

 tion of sulphate of zinc, with a large anode of this metal, must be 

 used in order to obtain a durable deposit. 



The different plans ibr gilding iron and steel without previous cop- 

 pering are omitted here, and I refer for those of Deebordeaux to Ding- 



