CHLORPLATINIC ACID BY ELECTROLYSIS 575 



residue weighed. The weighed mass of pure platinum is dis- 

 .solved in hydrochloric acid, with the addition of as little nitric 

 acid as possible, and, after cooling, filtered. The filtrate is after- 

 Awards evaporated in a porcelain dish on a water bath to a sirupy 

 consistence, taken up with water and filtered. To this filtrate 

 enough water is now added to make the solution correspond to 

 one gram of metallic platinum in 10 cubic centimeters. 



486. Preparation of Chlorplatinic Acid by Electrolysis. It has 

 been noticed when using aqua regia to dissolve plati- 

 num that traces of nitric acid are removed with great difficulty, 

 even by repeated evaporation. Weber has called attention to 

 the fact that when working with as much as 100 grams of plati- 

 num, repeated evaporation to dryness of the solution is tedious 

 .and yields unsatisfactory results. If hydrochloric acid be used 

 in the evaporation large quantities of material are necessary, 

 while with water there is danger of decomposition of the chlor- 

 platinic acid and consequent contamination with hydroxychlor- 

 platinates. 54 To avoid these conditions the following method 

 -of preparing the platinum reagent is used. 



Platinum scraps, or sponge, are dissolved in aqua regia, the 

 excess of acid removed either by neutralization or evaporation, 

 and the platinum solution reduced by zinc or alkaline formate, 

 preferably the latter. The liquid is decanted from the precipi- 

 tated platinum and the latter is warmed with a little dilute hy- 

 drochloric acid to remove iron. The platinum is transferred to 

 the electrolytic apparatus, which is constructed as follows: 



The apparatus (Fig. 47) is made of a cylindrical tube four 

 centimeters in diameter and 35 centimeters long, ending in a 

 narrow glass tube of about four millimeters bore, shaped in the 

 form of a siphon. The anode consists of a thin disk of sheet 

 platinum, closely fitting into the tube, and perforated with small 

 holes. A short piece of platinum wire is welded to the disk and 

 carried through the glass tube, as shown in the figure. The 

 -other end of the platinum wire ends in a glass tube which is 

 carried to the top of the apparatus and filled with mercury. The 

 platinum disk is about 30 centimeters from the top of the ap- 

 paratus, and is placed at a point where the tube begins to be- 

 54 Journal of the American Chemical Society, 1908, 80 : 29. 



