IN 



UNDULATORY FORCES. ELECTRO-METALLURGY. [TMTIKO SOI.DTIONB, we. 



bad quality, being gray, brown, or yellowish, sometimes 

 of a lilac hue, and generally in dull streaky vertical 

 lino* : all those evils may be mitigated by stirring tho 

 solution well every night after having finished plating, 

 or it may be entirely prevented by diluting tho liquid 

 with water to a proper extent, stirring it every evening, 

 and working it uniformly. All silvering and other de- 

 positing liquids exhibit this tendency to settle into strata 

 in working, especially if worked rapidly ; but the most 

 dilute ones show it in the least degree. 



If tho solution bo deficient in water, and contain a 

 gnat excess of free cyanide, tho foregoing evils are all 

 greatly aggravated. In hot weather it becomes very 

 unmanageable, and tho vapours of ammonia and hydro- 

 cyanic acid arising from it are quite overpowering. In 

 this case, the best way to improve it is to add cyanide of 

 silver and water in sufficient quantities to make it of a 

 good composition, keep it in a cool place, stir it daily, 

 and work it constantly in a uniform and careful 

 manner. New solutions, or old ones which have been 

 injured, often improve by daily stirring, with regular 

 and judicious working. An excess of cyanide of potas- 

 sium Is indicated when tho dissolving plates are very 

 strongly acted upon, and the deposit is at the same time 

 either very sparing or of a bad colour. 



If tho solution be too weak, i.e., if it contain too 

 much water, it conducts sparingly, deposits slowly, and 

 tho deposit has a dead-white appearance. This may bo 

 easily remedied by adding cyanide of silver and cyanide 

 of potassium to it in proper proportions, and working it 

 uniformly a few days with daily stirring. 



217. iraAing, Drying, and Ornamenting Silver-plated 

 Articles. Articles that have been plated with silver are 

 always washed in a running stream of water until every 

 trace of tho depositing liquid is removed from them ; 

 they are then immersed in hot, dry sawdust, moved 

 about in it, and gently rubbed with it until they ore 

 perfectly dry. After drying, they are, if necessary, 

 weighed, to ascertain how much silver has been put 

 upon thorn; then " scratched" (80), and finally finished 

 by burnishing, polishing, <tc. 



Sometimes, for the purpose of ornament, portions of 

 their surface are "oxidised." This is done by applying 

 a hot solution of bicliloride of platina (107) to them, 

 and allowing it to dry. The more platina the solu- 

 tion contains, and the hotter it is, the deeper black does 

 it produce ; or it may be effected by tho application of 

 the solution of "liver of sulphur." To produce a 

 brownish colour, apply a solution of equal weights of 

 sulphato of copper and sal-ammoniac in vinegar ; and to 

 produce a "dead" appearance, like frosted silver, de- 

 posit a more trace of copper upon it in a copper solu- 

 tion, then well wash it, and deposit a very thin layer of 

 silver upon this. In each of these cases tho parts 

 which are to remain bright must bo stopped-off with 

 varnish. 



218. " Stripping" Silver from Copper and Copper from 

 Silver. Occasionally the electro-plater has sent to him, 

 to be rcplated, old worn-out articles formed of "Shef- 

 field plate," in which the outer layer of silver has been 

 worn away, and portions of tho copper base beneath 

 are exposed ; these articles generally require to have tho 

 remaining portions of silver removed, in order to obtain 

 a uniform surface to deposit upon. The removal of the 

 silver is termed "stripping." To effect this, add a little 

 nitrate of potash (saltpetre) to a quantity of strong oil 

 of vitriol, and apply heat, until it is all dissolved ; then 

 immerse the articles in the hot liquid, and allow them 

 to remain until all the silver is dissolved. If the action 

 become slow, apply more boat or add more saltpetre ; 

 tho copper will not be much acted upon if tho articles 

 are not allowed to remain in too long. A number of 

 such articles are generally done together, and are after- 

 wards washed, and prepared in tho usual manner for 

 receiving a deposit. Tho silver may be recovered from 

 tho liquid, in the form of chloride of silver, by diluting 

 it with much water, then adding a solution of common 

 salt to it as long as a precipitate is produced : tho pre- 

 cipitate, when washed and dried, is chloride of silver. 



By fusing this with carbonate of potash, the metallic 

 silver is obtained. 



To remove copper from silver (which is but rarely 

 required), boil it in dilute hydrochloric acid, or imn 

 it in a hot solution of poromoride of iron. The 1. 

 solution may be made by adding peroxide of iron (cr. 

 jeweller's rouge) to hydrochloric acid as long as it will 

 dissolve; it will remove either tin, lead, or copper. from 

 either gold or silver, without affecting those metals. A 

 solution of chloride of zinc baa been used for the same 

 purpose. Copper may also be completely removed from 

 silver or gold, by making it tho anode in a sulpha' 

 copper solution until all the copper is dissolved ; the 

 silver will remain unaffected, if the current employed be 

 feeble and has not a greater intensity than one or two 

 cells. 



219. Tetling the Purity of Silver. M. Runge adopts 

 tho following method of testing the purity of silver : 

 Ho immerses the article in a mixture of 32 parts of 

 water, 4 parts of sulphuric arid, and 3 parts of chromato 

 of potash. If the metal bo pure, tho immersed part 

 quickly assumes a purple colour, which is less deep and 

 lively in proportion to tho amount of alloy contained 

 in the silver. No other metal exhibits the same colour 

 with this liquid. 



220. Testing the A mount of Silver and of Free Cyanide 

 in Silver Solution*. To ascertain tho amount of .- 



in a cyanide plating solution, add dilute sulphuric 

 to a known quantity of tho liquid as long as it produces 

 a precipitate ; wash and dry tho precipitate, which is 

 cyanide of silver containing in every 134 parts, 108 

 parts of metallic silver. To tost the amount of 

 cyanide of potassium, odd a solution of crystallised 

 nitrate of silver in distilled water to a known quantity 

 of the plating liquid, as long as the precipitate form. I 

 continues to be redissolved, and note how much 

 tallLscd nitrate is used ; every 175 ports expended indi- 

 cate 130 ports of free cyanide, or about throe parts of 

 free cyanide to four p.-ft-ts of nitrate of silver. 



221. Management of Gilding Solutions. Cyanide 

 gilding solution is generally kept in a glazed iron v< 

 and heated either by a stove, or by gas jets beneath ; or 

 in a stoneware or gloss pan immersed in boiling-v, 



On account of the general smalluess of the articles to bo 

 gilded, tho thinness of tho deposit required, and tho 

 rapidity of tho action in a hot liquid, tho article.! only 

 need to be immersed in tho solution for a few niin 

 when a thicker deposit is required, they should bo taken 

 out several times, brushed, and reimmersod. An 

 formed of iron or steel must bo coated with a thin film 

 of copper in tho cyanide coppering liquid before gilding. 

 The strength of battery used for gilding is goncr.il ly 

 about two cells of Smee's, of different sizes, accord i i 

 the magnitude of the articles to bo gilded. The I 

 water by evaporation is generally mode good hy adding 

 a little distilled water, after having finished gilding. 



222. Regulation of Colour in Eltctro-gUdinq. Tho 

 general method now adopted for regulating tho colour of 

 electro-gilding is as follows : After having prepared tho 

 solution, work it with a largo copper anode until tho 

 deposited metal begins to deteriorate in colour ; then 

 replace tho copper by a small gold anode. With the 

 copper anode can bo obtained a rich full colour, becom- 

 ing deeper as tho temperature of tho liquid is higher ; to 

 produce a paler yellow, use a small gold anode with tho 

 liquid at a lower temperature. 



223. Recovery of Gold and Silver from Depositing 

 Liquids. As both silver and gold solutions occasionally 

 get out of working condition, and become quite unlit for 

 use, it is very desirable that the operator should \i. 

 stand tho chemical action of different substances upon 

 them, and how to recover tho metal. Those of silver 

 generally get out of order, either from the addition of 

 too much "brightening liquid;" from excess of cyanidn 

 of potassium, together with tho heat of tho weather, and 

 injudicious management; from unsuccessful attempts to 

 improve tho condition of the liquid ; from the accidental 

 introduction of impurities; or from tho liquid knur; 

 been improperly mode. Supposing it to bo tho usual 



