DEPOSITION OF ALLOYS. 137 



Tin. Tin is easily deposited from a solution of protochloride of 

 tin. If the two poles or electrodes be kept about two inches apart, 

 a most beautiful phenomenon may be observed : the decomposition 

 of the solution is so rapid that it shoots out from the negative elec- 

 trode like tentacula, or feelers, towards the positive, which it reaches 

 in a few seconds : the space between the poles seems like a mass of 

 crystallized threads, and the electric current passes through them 

 without effecting further decomposition. So tender are these metal- 

 lic threads, that when lifted out of the solution they fall upon the 

 plate like cobweb. Seen through a glass, they exhibit a beautiful 

 crystalline structure. If a circular electrode of tin is used, and a 

 small wire put in the centre of the chloride solution, the thread-like 

 crystals will shoot out all round, and give quite a metallic conferva. 

 Tin may also be deposited from its solution in caustic potash or soda. 



Deposition of Alloys, Many attempts have been made to deposit 

 alloys of metals from their solutions. That two or more metals can 

 be deposited from a solution we have seen sufficient evidence ; but 

 the means to regulate the proportions of each, and to make such a 

 process practical, have yet to be discovered. It is hardly possible 

 to get a mixed solution of any two metals that are exactly equally 

 decomposable ; or, in other words, that the metals under the cir- 

 cumstances in which they are placed are exactly of equal conducting 

 power: hence the electric current will always travel through the 

 one that offers the least resistance, and there will be none of the 

 other metallic solution decomposed, or metal deposited, until the 

 quantity of electricity is greater than the best conducting metal in 

 the solution will allow to pass ; then the other metal will be depo- 

 sited in proportion to the extra electrical power that passes. As, 

 for example, take a mixture of cyanide of gold, silver, and copper, 

 in cyanide of potassium. The silver in this state is so much supe- 

 rior in its conducting power to the other salts, that all the silver may 

 be deposited from the solution by a weak battery without any of the 

 other metals : if the solution be afterwards heated, arid the battery 

 power kept so that no gas is allowed to escape from the articles, the 

 gold may be deposited without any copper ; but if the gas is allowed 

 to flow from the article receiving the deposit, the copper will be 

 deposited, and often more abundantly than the gold, as the escape 

 of gas is not consistent with a reguline deposit of gold. We have 

 thus deposited an alloy of gold and copper ; we have also deposited 

 gold and silver, but the alloy was very inferior and irregular. 

 Alloys can be obtained from silver and palladium, from cyanide 

 solutions, from zinc and copper, from a solution of their sulphates''; 

 but in no instance have we found good alloys, or alloys that could 

 pass as such in name or appearance. We have seen articles, such 

 as iron, covered with copper and zinc in this manner, or in alternate 



