CLEANSING PROCESSES.] UNDULATORY FORCES. ELECTRO-METALLURGY. 



229 



conductible by the battery process, the sulphate solution 

 (120) is in general use ; but for surfaces of tin, lead, 

 iron, or steel, the solution of cyanide of copper and 

 cyanide of potassium (120) is used. 



3rd. For the deposition of brass upon all ordinary 

 metals, the patented solution of Messrs. Morriss and 

 Johnson (127) is very successfully used ; the solutions of 

 Brunei (12G) and Salzede (125) arc also in practical use ; 

 and, in the United States of America, a solution very 

 ! similar to that of Messrs. Morriss and Co. is employed. 



4th. For depositing silver upon all common nietals, 

 the solution of double cyanide of silver and potassium 

 (135) is almost universally used ; the only exception is 

 where the double sulphite of silver and potash is used, 

 but only to a small extent, the magneto-machine being 

 in some cases employed. 



5th. For gilding all ordinary metals, almost the only 

 liquid used is the double cyanide of gold and potassium 

 (1 57 and 158) ; the only exceptions being a few minor 

 modifications for operations on the small scale. 



Cth. For platinising, the only solution in practical 

 use is the bichloride (1C7). 



7th. For solid deposition of silver and gold, the 

 patented solutions of Mr. Alexander Parkes (138 and 

 ICC) may be employed. 



171. Preparing Metal for Receiving a Deposit. The 

 rutypLst having acquired a general knowledge of 

 iting liquids, as well as of the necessary manipu- 

 ', and having made the several solutions necessary 



for his ordinary use, will require to prepare his articles 

 for receiving a deposit. All metallic articles must bo 

 cleaned, and otherwise prepared, before they are fit to 

 receive a deposit ; this preparation differs, of course, 

 according to the nature of the article, whether the 

 deposit be required to adhere firmly to the surface, or 

 merely to be used as a matrix, 'from which the deposited 

 metal is to be removed. 



172. Cast Iron and Zinc. Articles formed of zinc, 

 wrought-iron, cast-iron, or steel, are first immersed for a 

 few minutes in a boiling solution of caustic potash, to 

 remove any grease, tar, or oily substance which may bo 

 upon them ; they are then washed in water ; and those of 

 wrought or cast-iron are immersed in "pickling liquid" 

 (82), until the acid acts rather freely upon them ; rough 

 cast-iron requires a stronger liquid than smooth wrought- 

 iron : after being again washed in water, they are 

 "scratched" at the brush (80). If they are very coarse 

 castings or rusty articles, they may require several 

 Koakings in the dilute acid, and scourings with sand and 

 a harsh brush, and even filing, to make them quite 

 clean. 



173. Copper, Brass, and German Silver. Those formed 

 of copper, brass, or German silver, should be boiled in 

 the potash liquid, washed in water, and dipped into nitric 

 acid, or into the "dipping liquid" (82). They are then 

 to be washed in water, and dipped into a solution of 

 nitrate or cyanide of mercury (84), before immersing 

 them in the silvering solution. 



174. Sometimes, in order to assist in cleaning the 

 articles, they are suspended for a short time in the 

 depositing liquid, in contact with the negative pole of 

 the battery ; this dissolves the surface, and loosens their 

 impurities, unless they are very foul, or the solution is 

 too valuable. In every case they should be well rinsed 

 with water to remove the adhering acid, before dipping 

 them into the mercury solution, or immersing them in 

 the depositing vat. All objects which are to have a 

 d. -Unite weight of metal deposited upon them, are 

 weighed, and their weight noted down after they have 

 been cleaned. 



175. Wiring A rticles. The articles having been cleaned 

 thoroughly, have wires of copper attached to them, to 

 suspend them in the vat. The wires differ in size with 

 dilferent articles ; with small ones, such as spoons, knives, 

 forks, snuffers, teapots, jugs, and such articles, size No. 

 20 or 22 of the Birmingham brass wire gauge, and about 

 eighteen or twenty inches long, are used. Very large 

 articles, such as fire-irons, fenders, hat-stands, and 

 articles of ornamental iron-work, are suspended in the 



solution by strong copper or brass hooks ; in some cases 

 where a powerful and certain connection is required, the 

 wires are soldered to the articles. 



17C. Preparing Articles for Adhesive Deposits. We 

 have already explained how necessary it is that all 

 articles intended for the depositing vat should be cleaned 

 in the most perfect manner possible, before being im- 

 mersed in the depositing liquid, otherwise the deposit 

 will not adhere. Articles of copper, brass, or German 

 silver, which are to be silver-plated, should also be 

 dipped into one of the solutions of mercury (84); other- 

 wise the deposit will not adhere at all, or will vary in 

 appearance in different parts; and in consequence of 

 this perfect degree of cleanliness required, the cleaning 

 of them often involves more trouble than the depositing. 

 All articles should be plunged, while still wet from the 

 cleaning process, into the depositing vat. The practical 

 miimtitu of preparing the surfaces of different metals for 

 receiving adhesive deposits of other metals, vary in 

 almost every manufactory, and much information yet 

 remains to be developed upon this point For want of 

 this knowledge, the most skilful operators sometimes 

 fail in producing perfect adhesion, especially upon zinc, 

 cast-iron, steel, and Britannia metal. 



177. Preparing Metals for Non-adhesive Deposits: 

 Metal articles which are to receive non-adhesive deposits, 

 such as medallions, of which copies are desired in copper, 

 should be allowed to remain a sufficient time to slightly 

 oxidate after being cleaned, before being plunged iu the 

 depositing vat, the oxide preventing adhesion. In some 

 cases they are rubbed over with cotton wool slightly 

 moistened with a very weak solution of bees-wax dis- 

 solved in camphiue, in the proportion of a piece of wax 

 of the size of a small pea, in a quarter of a pint of the 

 spirit ; others use a little sweet oil, which is immediately 

 wiped off with a fresh piece of dry cotton wool. 



178. "Stopping off" to Prevent Deposition. Many 

 articles which are to receive deposits require to have 

 portions of their surface "stopped off," to prevent the 

 deposit spreading over those parts : for instance, in 

 taking a copy of one side of a metal medallion, the 

 opposite side must be coated with some kind of varnish, 

 wax, or fat, to prevent deposition ; or in gilding the 

 inside of a cream jug which has been silvered on tho 

 outside, varnish must be applied all round the edge on 

 tho outside for the same reason. For gilding and other 

 hot solutions, copal varnish is generally used; but for 

 cold liquids and common work, an ordinary varnish, 

 such as engravers use for a similar purpose, will do very 

 welL In the absence of other substances, a coating 

 of sealing-wax dissolved in naphtha will answer every 

 purpose. 



179. Moulding and Copying Works of Art. The 

 electrotypist who includes iu his business the multipli- 

 cation of works of art, as well as the simple plating of 

 metal articles, will require a knowledge of tho art of 

 moulding. To copy both sides of a metallic coin or 

 medal in the mixture of gutta-percha and marine glue 

 recommended (85), take a strip of thin sheet copper, 

 brass, or tinned iron, about an inch wide ; wind it closely 

 round the edge of the medal, and solder its ends toge- 

 ther ; wipe the medal and take two balls of the com- 

 position, quite hot and soft, and press them simulta- 

 neously against the two faces of tho medal, working the 

 material from the centre towards the circumference to 

 exclude bubbles of air ; place two thick plates of cold 

 metal, one on eacli side, and gradually screw up the 

 whole in a vice, or screw-press, gently at first, but in- 

 creasing the pressure to a high degree as the materials 

 become hard. When it is quite cold, which will be in 

 about two hours, the two copies may bo easily removed 

 from tho original, by inserting the end of a gimlet in 

 their backs, and drawing them out ; they are easily re- 

 moved, because the composition slightly contracts in 

 cooling. They will present fine impressions of the 

 original, and be perfectly free from air-bubbles, when the 

 operation has been carefully performed. 



180. Elastic Moulding. If the medallion bo under-cut, 

 it must be copied in "elastic moulding" (86), thus: 



