1892.] on Electro-Metallurgy. 633 



But tlie use of the burnisher is not the only means available for 

 the production of a smooth deposit. It was observed in the early 

 days of electro-plating how great a change was effected in the character 

 of the metal deposited, by the presence of a very small quaatity of 

 certain impurities. It was found, for example, that an exceedingly 

 minute dose of bisulphide of carbon, if put into a bath from which 

 silver was being deposited, caused the deposit to change from dull to 

 bright. 



I have lately had experience of a similar kind vp-ith nickel and 

 with copper. I was working with a hot solution of nickel, and up 

 to a certain point the deposit had the usual dead-grey appearance. 

 Suddenly, and without doing anything more than putting in a new 

 cathode, I found the character of the deposit completely changed. 

 Instead of the grey, tough, adherent deposit, there was produced a 

 brittle, specular deposit, which scaled off in brilliantly shining flakes 

 of metal. I sought for the cause of this extraordinary change, and 

 traced it to the accidental introduction into the solution of a minute 

 quantity of glue. 



By adding gelatine to a fresh nickel solution I obtained the same 

 peculiar bright and brittle deposit that had resulted from the accident. 

 I then made a similar addition to a solution of copper, and when I 

 hit the right quantity — an exceedingly minute one — bright copper, 

 instead of dull or crystalline, was deposited. Here are some speci- 

 mens. These were deposited on a bright surface, and they are bright 

 on both sides. 



Not only is the copper made bright, under the conditions I have 

 described, but, if the proportion of the gelatine be carried to the 

 utmost that is consistent with the production of a bright deposit, it 

 becomes exceedingly hard and brittle. Beyond this point the deposit 

 is partly bright and partly dead, the arrangement of the patches of 

 dead and bright being in some cases very peculiar, and suggestive 

 of a strong conflict of opposing forces. 



Before I leave the subject of copper deposition, I may mention 

 that I have found the range of current density within which it is 

 possible to obtain a deposit of reguline metal, far wider than is 

 commonly supposed. 



The rate of deposition in copper-refining is usually very slow, and it 

 is one of the drawbacks of the process, since slow deposition necessi- 

 tates large plant. But rapid deposition necessitates a larger con- 

 sumption of power, and larger cost on that account, and therefore, 

 there is a point beyond which it is not good economy to go, in the 

 direction of more rapid deposition. Still there are cases, where, if 

 we had the power to deposit more rapidly, it might be found useful 

 to exercise it. The subject of more rapid deposition is also interest- 

 ing from a scientific point of view, I therefore mention an unusual 

 result I have arrived at in this direction. 



Taking, as one extreme, the slow rate of deposit, of one ampere 

 per square foot of cathode — a rate not infrequent in copper-refining, 



Vol. XIII. (No. 86.) 2 u 



