218 



UNDULATORY FORCES. ELECTRO-METALLURGY. [DEPOSITING LIQUIDS. 



in tho liquid ; if cither beoome eoatod with metal in an 

 hour, that one in positive; but if neither become coated 

 in nix hours, there is no perceptible electric difference 

 U>twen them. 



93. The following experiments bear upon this part of 

 the subject, and ahow that if a liquid contain two 

 metal* in solution, and a wire or other piece of each of 

 those metals be immersed in tho liquid, and one becomes 



rod with a deposit of metal, while the other does 

 not, the one so covered is electro-positive to the othor in 

 that liquid, and the solution will only yield the same 

 metal which u deposited by simple immersion. 



Krixrimtnt 51. With an alloy solution consisting of 

 equal measures of a strong solution of protochlorido of 

 tin, and tcrchloride of antimony, with an anode either of 

 tin or antimony (the latter is the most proper, because it 

 does not coat itself by simple immersion in the liquid), a 

 copper cathode, and two small cells of Smee's battery, 

 only antimony was deposited; tin coated itself with 

 antimony in this solution by simple immersion, and was 

 found by tho galvanometer to be strongly positive to 

 that metal. 



Experiment 62. With a liquid composed of equal 

 measures of a solution of protochloride of tin and 

 chloride of bismuth, and either a bismuth or tin anode 

 (the former is the best), a brass cathode, and two cells of 

 Smee's battery, only bismuth was deposited ; tin was 

 positive to bismuth in this liquid by the galvanometer, 

 and coated itself quickly with that metal by simple im- 

 mersion. 



Experiment 63. With a mixture of equal measures 

 of tcrchloride of antimony, and chloride of bismuth, 

 antimony anode, copper cathode, and a feeble Smee's 

 battery, only antimony was deposited ; bismuth coated 

 itself slowly with the antimony in solution by simple 

 immersion, and was found by tho galvanometer to be 

 moderately positive to the latter metal 



Experiment 54. With 100 grains each of protocliloride 

 of tin and chloride of zinc dissolved together in an 

 ounce of distilled water, tin anode, copper cathode, and 

 one cell of Smee's battery, only tin was deposited ; zinc 

 was positive to tin in this liquid by the galvanometer, 

 and deposited tin upon itself by simple immersion. 



Experiment 65. With equal measures of strong solu- 

 tions of nitrate of zinc, and ternitrate of bismuth, and a 

 little nitric acid, bismuth anode, copper cathode, and a 

 feeble one-pair battery, only bismuth was deposited ; 

 siinc was strongly positive to bismuth in this liquid by 

 tho galvanometer, and coated itself quickly with that 

 metal by simple immersion. 



Experiment 60. With a solution of the mixed sul- 

 phates of zinc and copper, copper anode and cathode, 

 and a single small battery, copper alone was deposited ; 

 zinc was strongly positive to copper in tliis liquid by the 

 galvanometer, and coated itself immediately with copper 

 in it by simple immersion. 



94. Further, if we take some distilled water, and 

 caustic potash be dissolved in it, on passing a mode- 

 rately strong current through it by phitina electrodes, 

 hydrogen gas will alone be set free at the cathode : iu 

 this case, also, hydrogen the least positive of the two 

 positive elements of the liquid potassium and hy- 

 drogen is set free or deposited. If we now add a little 

 sulphuric acid to the liquid to convert it into a solution 

 of sulphate of potash, with some sulphate of zinc be- 

 sides, and pass a weak current through, we shall obtain 

 a deposit of zinc on tho cathode, but no hydrogen or 

 potassium: in this case wo cannot determine by the 

 galvanometer which is the most positive in this liquid, 

 hydrogen or zinc, because the former is a gas ; but it is 

 probable that hydrogen is the most positive, because 

 zinc does not evolve it by simple immersion in this 

 liquid. If we further add to the liquid a small quantity 

 of sulphate of copper, and treat it as before, neither 

 potassium, hydrogen, nor zinc will be deposited, l>nt 

 only copper ; and we find by the galvanometer, that 

 C"]>IM.T is less positive than zinc in such a liquid, and 

 that zinc coats itself with copper in it by simple im- 

 mersion : in this case, also, the least positive of the posi- 



tive elements of the liquid is alone deposited. From 

 these and many othor experiments, which we liave t 

 with similar results, we deduce tho following rule : If 

 a liquid contain several metals or uther electro-positive 

 substances dissolved, and a weak electric current be 

 passed through it, only tliat substance which is the leant 

 electro-positive will bo deposited. 



AY \\ iih regard to the influence exercised by the 

 proportions of the ingredients of tho liquid, anil tlu> 

 strength of the current, we may observe, that, if a 

 liquid contain several metals dissolved in equal quan- 

 tities, and only one is being deposited by tlie pos:r 

 a weak current, a considerable increase in the MM -nyth 

 of tho current will cause a portion of the next IIK.I-O 

 positive metal to be deposited along with the less 

 positive one ; but this alloy deposit will not bo \ 

 coherent, because the power required to deport, the 

 second metal in the roguline state will be so great as 

 to deposit the first as a soft powder. This holds most 

 true when tho difference of electric power required is at 

 a maximum. For instance 1st. If small and equal 

 quantities of sulphate of zinc and sulphate of copper 

 ore dissolved together in a large quantity of water, and 

 a feeble current be passed through the solution, only 

 reguline copper will be deposited ; but if the battery 

 power be considerably increased, either by a greater 

 number or larger surface of the battery plates, the 

 deposit of copper will cease to be reguline, and zinc 

 will be deposited with it. If the power be still further 

 increased, hydrogen gas will also be evolved at the sur- 

 face of the deposited metals. 2nd. If we dissolve a 

 small quantity of sulphate of copper, and a great quan- 

 tity of sulphate of zinc, in a large quantity of water, 

 and pass a strong current through the solution, copper, 

 zinc, and hydrogen will be set free at the cathode. 3rd. 

 If we slightly moisten a lump of caustic potash with 

 pure water, and pass a weak electric current through it 

 by pLitina electrodes, hydrogen alone will bo set free at 

 the cathode; but if a very powerful current be employed, 

 potassium also will be deposited. In each of these cases 

 we find, that when the current is weak, the least positive 

 of the positive substances is alone deposited ; but if tho 

 power be sufficiently increased, and there is only a 

 small proportion of the less positive substance present, 

 the more positive substances, even though they are much 

 more positive, will also be deposited. Thus the weaker 

 affinities are overcome first, and to the greatest extent ; 

 the current of electricity exercising its influence first, 

 and in the greatest proportions, upon the salt of tho 

 least positive metals. 



90. Depositing Liquidt. For the benefit of the prac- 

 tical depositor, to whom a general knowledge of all 

 solutions from which ordinary metals may be deposited, 

 with their respective advantages and disadvantages, is 

 of considerable importance, we will give a description of 

 those solutions in regular order, making such remarks 

 in our progress as will bo likely to assist him in 

 the selection of those most suitable for his particular 

 purposes. 



97. Antimony Solutions. The most common salts of 

 antimony are the sulphide, tcrchloride, and potassio- 

 tartrato. The hydrochlorate of terchloride of antimony, 

 i.e., the ordinary chloride or butter of antimony, as pre- 

 pared for pharmaceutical purposes, is formed thus : 

 Take ono pound of black sulphide of antimony ; odd to it 

 four pints of hydrochloric acid ; gently heat tho mixture 

 with constant stirring, until tho gas evolved decreases ; 

 then boil it slowly down to two pints, keeping it partly 

 covered all the time ; cool, and filter through calico, 

 and keep it in a stoppered bottle. It is a yellowish- 

 red liquid, of specific gravity 1 '47, but becomes nearly 

 colourless by depositing antimony by tho battery 

 process. 



A similar solution may be made by the battery 

 method; this consists in passing a current from sevi ral 

 pairs of batteries through strong hydrochloric acid by a 

 arge anode of antimony, until a good deposit is ob- 

 tained : this solution is nearly colourless. Thn chloride 

 of antimony b an excellent conductor of electricity ; it 



