92 COATING OF IKON WITH COPPER. 



place, and no deposit will be made, except as the effect of the electric 

 current introduced by the battery. This we believe is the cause why 

 De la Eive, Spencer, and others, failed, at an early stage of the art, 

 in their experiments in plating and gilding, as they employed acid 

 solutions, which are quite impracticable when used for depositing 

 upon inferior metals. Under these circumstances, other solvents for 

 the metals must be used, which have a different relative attraction 

 for the metals than the acids have. The substance first applied for 

 this purpose is, after twelve years' experience, still found to be the 

 best namely, cyanide of potassium. 



Cyanide of Potassium. This substance may be prepared by ex- 

 posing ferrocyanide of potassium (yellow prussiate of potash) to a 

 red heat in an iron crucible ; then pounding the mass, and boiling 

 it in alcohol of about spec. grav. 0.900 : cyanide of potassium crys- 

 tallizes on cooling the resulting solution. It is now, however, 

 almost universally prepared for electro-metallurgical purposes, by a 

 process which was first suggested by Messrs. F. and E. Rodgers, 

 but afterwards more fully explained by Prof. Liebig, and hence 

 called " Liebig's Process": it is at once both simple and easy of 

 performance. 



Ferrocyanide of potassium, pounded fine, is dried over a slow 

 fire (we have found an iron plate, or clean shovel, to serve the 

 purpose very well); it must be constantly stirred to prevent its 

 forming a cake upon the hot iron ; when perfectly free from 

 moisture, 8 parts must be thoroughly well mixed with 3 parts of 

 carbonate of potash, also well dried : put a cast-iron crucible into 

 the fire, and, when it is red hot, nearly fill it with the mixture, and 

 keep up the heat by occasional augmentations of fuel : the crucible 

 should be kept covered as much as possible. In a short time the 

 whole fuses into a beautiful liquid with the evolution of gas. It 

 should be kept in this state for 10 or 15 minutes, being occasionally 

 stirred with an iron rod : the portion adhering to the rod should 

 be examined from time to time, and when the liquid on it cools 

 white, it is an indication that it is ready to be removed from the 

 fire; but the first time a cast-iron crucible is used, this test will 

 not be so accurate, the salt having then a light grey colour. When 

 the crucible is removed from the fire, it should be placed upon a 

 stone, the mass stirred, and then allowed to settle for a short time, 

 after which the clear, or liquid part, is to be poured off into a clean 

 iron vessel. The sediment should be scraped clean out of the 

 crucible while it is hot, as the crucible will do to use again several 

 times ; but if the mass at bottom be allowed to cool, it will be 

 difficult to remove it from the crucible afterwards. The clear 

 liquid poured off is cyanide of potassium, having from 25 -to 30 per 

 cent, of cyanate of potash, and other impurities generally contained 



