82

ELECTRO-METALLURGY.

It has been found that with cyanide solutions of gold and silver in the ^ e( , 0 jo-chemical apparatus, the nascent cyanogen at the positive pole or plate, in a „jell’ sposition cell, will act .upon and dissolve gold and silver. Two or three of E® 0 fcylindric cells, as shown at a in fig. 41, of a pint size, for acting upon soluti

gold or silver, will in general suffice. The'decomposition cell b is made of o ce llporcelain. The zinc may be amalgamated, and excited with brine; the e°P‘ (0 (liecontains, as usual, a solution of blue vitriol. To the end of the wire attache ^ 0 jcopper cylinder of the battery, a plate of silver or gold is affixed ; and to the or gilt-the wire attached to the zinc cylinder is affixed the mould, or surface, to be P‘® J5gu re

The plates of silver or gold and zinc should be placed face to face as shown m j c gre e

in the decomposition cell; which is filled by the cyanide solution. A certai ^ f r stof heat favors the processes of electro-gilding and plating. The surface is de inobtained, but it may be easily polished with leather and plate-powder, and buiwhole or in parts with a steel or agate tool.

In March, 1840, Messrs. Elkington obtained a patent for the use of parid 11 ^potash, as a solvent for the oxides of gold and silver in the electro-chemicalfor plating and gilding metals. They also “ sometimes employ a solution ol 1 jj, e ir

(purple of Cassius) in the muriates of potash, Ac.” The chemical misnomerb ^ 1°specification, are very remarkable, and do great discredit to the person crn i’ ( j;j]'ere ntdraw it up. Prussiate of potash is the ordinary commercial name of a salt rer ^ an d th efrom the cyanide of potassium—the substance really meant by the patenteespurple of Cassius is very different from protoxide of gold. . n bri?' 1 *’

In plating or gilding great care must be bestowed in making the articles cic ^uldand perfectly free from the least film of grease. For this purpose, they dipfboiled in a solution of caustic alkali, then scoured with sand and water, ^ cyn®. 11 ^into a dilute acid, and finally rinsed with water. A solution of the nitrate folio'* 1 * 0of mercury may also be used with advantage for cleaning surfaces. I*metals have been deposited by electro-chemistry :— . ^ 011 ®^"!*’

Gold, platinum, silver, copper, zinc, nickel, antimony, bismuth,cadmium, lead, and tin; of these, the first five are the most important a ^ ^ sol utl °jjThe gilding solution may be prepared by placing slips or sheets of gm® 1 ‘ a s®®

of cyanide of potassium, and attaching to the negative pole of a voltaic latter c0 'rplate of gold, but to the positive pole a much larger one; whereby tn ^ abines with the cyanogen, under the influence of positive electricity, “"Ivbedi^Uon. Or, oxide of gold, precipitated from the chloride by magnesia? im .in the solution of the cyanide.

For making copper medals, &c., a plate of amalgamated zinc is t0 - tll dilute - ,vessel of unglazed earthenware, or of any other porous substance, fill® pitched ,r ° n aphuric acid ; which vessel is set into a trough of glass, glazed pottery, oi g j 0 i 9 UP 0containing blue vitriol in the state of solution, as well as in the state o .perforated shelf, near the surface of the liquid. _ w ire t® me

The moulds^ to be covered with copper are to be attached by a copp t ], a t of ^ ezinc plate. The surface of zinc excited by the acid should be equa ou jd, shot”moulds; with which view a piece of zinc, equivalent in size to the -j c

suspended in front of it. ferrocf* g f

For depositing copper upon iron, Messrs. Elkington use a solution ^ sU Iplmt*of copper in cyanide of potassium in the decomposition trough, instea ^ ^ cO®copper, neutralized from time to time with a little caustic alkali, as