UNDULATORY FORCES. ELECTRO-METALLURGY. [QENKHAL nuiw. 



191. If we are producing a rogulino deposit, with 

 one-cell arrangement, in a good depositing liquid, 

 with eU-ctrode* of the tamo size as the immersed portion 

 of the battery plates, and it is wished to change the 

 deposit to a soft black powder, the platen of the battery 

 must be immened considerably deeper in the liquid, and 

 a Tory much larger dissolving plate in the vat used. 



1 If wo wish to change the deposit to a crystalline one, 

 several more pairs of battery should be put on, con- 

 nected intensity-fashion, and the plates must bo im- 

 mersed to an exceedingly small depth in their liquid*, 

 and a Tory small anode employed. These results ha\ , 

 a direct reference to the size of the roceiTing surface : 

 for if, with any giTcn battery and anode, wo are pro- 

 ducing a black powder deposit upon a very small article, 

 a larger article would receive a rogulino deposit, and a 

 much larger one would have thrown down on it a do- 

 posit bordering upon the crystalline state. Thus it will 

 bo perceived that the black powder deposit is a result of 

 too rapid, and the crystalline one of too slow action. 



192. Spread of Deposit. If wo wish to make a de- 

 posit spread rapidly over a metal of inferior conducti- 

 bility, such as a long iron rod, we must use a current of 

 high intensity and rather small quantity ; thLs will drive 

 it ovor tho surface without causing it to become soft or 

 non-coherent. Tho action of such a current appears to 

 consist in conferring upon the particles a kind of polarity, 

 a power of grouping themselves into separate warty 

 nodules or crystals, each of which, as it becomes larger, 

 appears to powerfully ropel its neighbour, and thus causes 

 the metal to spread rapidly; when this action is con- 

 tinued to a considerable thickness of deposit, especially 

 in cold weather, the metal is exceedingly hard, and easily 

 broken into a number of distinct grains or nodules, which 

 are in tho form of warty lumps with rounded edges. 



u tho action has been rather too quick, or tho liquid 

 not sufficiently cold, and composed of more or less per- 

 fect crystals, with edges sometimes beautifully defined, 

 or when the action has been very slow, and tho liquid 

 very cold and undisturbed, the same occurs. With tho 

 intensity of one hundred pairs of Smoo's battery, acting 

 for a long period of time in cold weather, and the quan- 

 tity of the current kept down to tho lowest possible 

 degree, wo have seen a tough deposit of zinc spread 

 over several square inches of clean gutta-percha; and 

 in depositing copper with a current of rather high in- 

 tensity, and small quantity, upon hlackluadcd gutta- 

 percha medallions, we have repeatedly observed, that 

 whore there was a sunk boundary line near the edge, 

 the deposit remained quite thin, as if powerfully re- 

 pelled, whilst on each side of the line it was very thick, 

 and on the outside edge, accumulated in large warty 

 masses, hard ami distinctly separate, and containing as 

 much metal as the whole of tho inodalliou besides. 



inagemcHt of Batteries. Tho most suitable 

 strength of liquid for filling the battery colls, consists of 

 one measure of sulphuric acid and about twenty mea- 

 sures of water ; a stronger liquid may bo used, oven to 

 one part of acid to ten or twelve parts of water; but 

 then tho zinc plates require constant watching and fre- 

 quent amalgamating, to prevent waste. If the acid 

 liquid be very strong, and the electric action energetic, 

 tho zinc plates will require to bo examined every day, 

 to see that there is no local action, i.e., chemical action 

 in particular places; and when gas is found to bo frcoly 

 rising from them, as well as from tho silver or copper, or 

 when any dull patches appear where tho acid has acted 

 too strongly upon thorn, they should bo taken out and 

 amalgamated. They should be frequently amalgamated 

 when new ; and afterwards, if much worked, they should 

 bo amalgamated every few days : when they become old 

 they should bo rarely amalgamated, because it very much 

 weakens tho power. When they become so thin as to 

 fall to pieces on handling, now plates should bo si: 

 tutod, and the old should cither bo molted at as low a 

 degree of heat as possible, to prevent loss of mercury, 

 and cast into rods for Dauioll's batteries ; or bo broken 

 up, put in an iron retort, and tho mercury distilled from 

 thorn at a strong rod heat into a vessel of water. 



194. The zinc plates should bo taken out of tho liquid 

 every evening, unless deposition is required to coat in uo 

 all night After the battery has been at work a few 

 days, a little more acid should bo addod, and tho liquid 

 stirred ; and this should bo done as often as tho power 

 gets low, until at length tho liquid becomes thick and 

 nearly saturated with zinc salt, which crystallises about 

 the edges of tho cells. It is then timo to throw it away 

 and put fresh, or it may be filtered, evaporated, and 

 crystallised, and tho resulting salt (sulphate of zinc) pro- 

 served for depositing purposes. If any of tho silver or 

 copper plates of the batteries become covered with a 

 deposit of zinc whilst working, it shows that all the acid 

 in that coll is exhausted, and that more should bo ad<l I. 

 or fresh liquid put in. This only happens in a Smoe'a 

 battery, or in tho old zinc and copper arrangement. 

 Tho deposit of zinc may bo easily and quickly removed 

 l>y tho addition of acid to that coll, by a fivsli liquid, <>r 

 by immersing tho coated plate in dilute sulphuric acid as 

 long as gas is evolved from it 



195. If copper plates are employed in the batteries, 

 they should be heated red-hot all over every week or 

 ten days, and quenched in water, and then dipped in 

 " dipping liquid'' (82), or in nitric acid ; and if platinised, 

 silver plates are used, they should bo re-platinised an 

 often as they become light in colour, or their power 

 becomes low, which will happen once in two or i 

 months! with constant working. Tho re-platinism;.; 

 greatly increases the power of the battery. Great care 

 must bo taken that the zincs never touch the silver or 

 copper plates when wot, otherwise the morcury will got 

 upon the latter, and much weaken tho battery power; 

 and the silver plates will drop to pieces if they are very 

 thin. 



196. General Rules for Working Solutions. In working 

 any depositing liquid 1st, avoid doing anything which 

 will alter tho chemical composition of the liquid, or cvm 

 the proportions of its ingredients, except tho water that 

 may bo altered, in proportion, in most liquids without 

 much inconvenience ; 2nd, adapt your electric power to 

 the liquid, rather than the liquid to the power, and 

 regulate the deposit rather by alterations in tho battery 

 than by alterations in tho depositing vessel, except as 

 regards the distances of tho electrodes or the tem- 

 perature of tho liquid those may bo altered with safety, 

 and, sometimes, with convenience ; and 3rd, as a general 

 rule, let your dissolving metal, the anode, expose a larger 

 immersed surface than the receiving article, tho cathode. 



197. Position of Articles and Dissnlriny J'lates. Tho 

 best practical position for the dissolving plate is tho 

 vertical, tho dissolving plate and tho receiving article 

 being suspended in tho liquid facing each other, tho latter 

 being rather tho lowest of the two, and both wholly im- 

 mersed. The horizontal position, with the dissolving 

 metal above, although tho most philosophical arra 

 ment, does not succeed in practical working, because tho 

 metal used for dissolving, is never quite pure (with 

 copper, especially), and the impurities from it fall upon 

 the surface of tho receiving article l>eneath, and make it 

 rough; in addition to this, tho position of tho article 

 prevents our being ablo to examine it easily or remove it 

 conveniently. If the article to be coated have a very 

 ijTegular outline, either the dissolving plate should be 

 bent somewhat to its form, so that the two may be nearly 



listant at all parts ; or tho article should bo often 

 shifted in its position, so as to produce a nearly uniform 

 thickness of deposit all over. The nearer tho receiving 

 article is to the dissolving plate, tho moro rapid is tho 

 deposit ; and a largo body of liquid deposits more ripidly 

 and more evenly than a small one ; largo connecting 

 wires are moro favourable to quick deposits than small 

 ones. Tho greatest thickness of deposit always i 

 place upon the most prominent places, i.e., upon those 

 parts nearest the dissolving metal. 



198. Motion of Articles in V<A. In some solutions 

 for instance, tho double sulphite of silver and potash if 

 tho current bo too strong to produce a good deposit, 

 motion of tho articles will prevent it becoming bad. In 

 some plating establishments, the articles in the vats are 



