75 



YI. 



Burnisbiiig the foil with a smooth bent glass rod, or ^yitb a piece of 

 bard wood, made the pbitiiuim denser. Lightly beating the foil between 

 chamois skins was of some assistance, though for the purpose in view 

 great care had to be exercised to prevent getting the deposit of unequal 

 thiclcness over the foil. 



YII. 



There are many liquids that will dissolve the copper— notably, nitric 

 acid, but, on account of the formation of gas during the reaction and the 

 consequent tearing of the foil, it and several others bqd to be discarded. 

 Ammonium cliloride was found to be the best, though its action is very 

 slow. The result may be hastened, however, by first making this foil of 

 copper, the anode in a copper sulphate electrolyte and dissolving away 

 a large part of tlie copper before putting the foil in tlie bath of ammonium 

 chloride. 



There is one serious dithculty that is met in dissolving the copper. 

 After all the copper has been dissolved, it is extremely difficult to re- 

 move the foil from the liquid on account of the cohesion being sufficient 

 to add enough weight of water to the foil to tear it as it is taken from 

 the liquid or roll it up so that it is useless. 



This can only be overcome by placing the foil where it is to go when 

 completed, and then dissolve away the copper. 



Although some very fair foils were made in these experiments, it is 

 hardly fair to say that they were wholly successful. But the work opens 

 up another avenue that may lead to something veiy useful— the electro- 

 plating with platinum of delicate sin-gical instruments, etc.. to take the 

 place of nickel. It is well known that many efforts have been made to 

 use platinum for such purposes, but, as far as the writer knows, with very 

 indifferent success on account of the great trouble and consequent cost of 

 the work. TJsing an electrolyte of platinate of potassium, it is possible to 

 keep it constantly saturated by simply keeping a bag of platinic hydrate 

 hanging in the solution; the process is comparatively rapid and needs lit- 

 tle attention after once started. The plated article will stand consider- 

 able amount of usage, and, of course, will not tarnish under any ordinary 

 circumstances. 



