73 



Experiments gave the Iwghest current density that could be used 

 without the appearance of platinum black, as being about .0001 amperes 

 per square centimeter, and even then there was a slight appearance of gas 

 at the cathode. The liquid was of a clear straw color when warm, becom- 

 ing purple on cooling; but, after allowing the current to run for about 15 

 minutes, a dark cloudy appearance was noticed at the anode that gradu- 

 ally spread to the whole liquid. No chemical analysis was made to de- 

 termine the composition of this, though it is very likely that it was plat- 

 iuous hydrate. The liquid was then tightly stoppered and left for about 

 two months, when it was found that all the platinum had been reduced 

 to the form of spongy platinum. This was due to the fact that oxalic 

 acid is an active reducing agent. 



Taken as a whole, the experiments with oxalate of platinum were 

 very unsatisfactory, the current being low, the solution unstable and the 

 deposit dark, as if some of the dark precipitate was occluded in the 

 deposif. 



Mention is made of these trials for the reason that the results are 

 contrary to the statements of Dr. Wahl. 



The next solution tried was made by dissolving platiuic hydrate in 

 caustic potash in the proportions— 

 1 oz. platinic hydrate, 

 4 oz. caustic potash, 

 2000 c.c. distilled water. 



It was possible to use a current density of .003 amperes per square 

 centimeter and get a bright smooth deposit, when the liquid was held at 

 a temperature of Go F. When the deposit was made comparatively thick, 

 however, there was some appearance of crystallization. Trial showed 

 a current density of .002 to be about as high as it was best to go with 

 this particular solution at the above temperature. 



IV. 



Tests were now made to determine the effect of varying the concen- 

 trations of the liquid. As above noted, when the proportions were— 



1 oz. platinic hydrate, 



4 oz. caustic potash, 



2000 c.c. distilled water, 

 the maximum current density that could be used and get a clear, bright 

 deposit was .0035 amperes per square centimeter. 



