Lea — Platinochlorides and Platinum Suhchloride. 399 



taking an ordinary water stove of the kind in which a chamber 

 is surrounded on five sides by water. Such a stove is to be 

 furnished with a Kekule constant level, regulated to keep the 

 water jacket half full. If now the heat is turned on so as to 

 keep the water gently boiling, it will be found that solutions 

 placed on the top maintain a perfectly steady temperature, vary- 

 ing, from 55° to 72° C. according to the shape of the vessel, 

 but constant for any one shape. The lowest temperature, 

 about 55°, is obtained with an open, flat porcelain basin. It 

 rises gradually as the shape of the vessel tends more to check 

 evaporation. When a liter flask has about 2 inches of solu- 

 tion the temperature will remain steady at about 66° and this 

 temperature is very suitable for the treatment just described. 



Even with this excess of reducing agent 10 or 12 hours will 

 be required. The solution must not be allowed to evaporate 

 to less than one-half its original bulk. 



The completion of the operation is known by the solution 

 showing a perfectly pure ruby red color. The slightest shade 

 of orange indicates the presence of the yellow platinic salt. 

 It is much safer to allow the solution to evaporate spontane- 

 ously. If evaporated by heat there is always a chance that 

 the reduction may go too far. 



There is not much to choose between these two methods. 

 The first, with acid sulphite, is the safest, because there is no 

 danger of carrying it too far. On the other hand in the 

 second method the red salt separates more easily and com- 

 pletely in crystallizing. 



On the whole the method which I prefer is to keep down 

 the hypophosphite and use a higher temperature and longer 

 heating. For this, a weighed quantity of platinum salt may 

 be placed in a flask with 30 cc of water for each gram of the salt 

 and a quantity of potassium hypophosphite equal in weight to 

 ^ of the platinum salt. The flask is to be placed in a water 

 bath which is kept at 80° to 90° C. In consequence of the 

 small proportion of hypophosphite the action is slow, requir- 

 ing about 18 or 20 hours for complete conversion. No atten- 

 tion during this time is required and the advantages are that 

 the solution becomes sufficiently concentrated to crystallize on 

 cooling and that the very small quantity of foreign matter 

 introduced renders it easy to obtain a pure product. 



At 100° C. the reduction to red salt takes place in about 

 fifteen minutes. This method is practicable, but requires 

 great circumspection. If the boiling is continued a little 

 too long, the solution suddenly turns brown ; the reduction has 

 gone too far. 



If a quick reduction is desired it is better to use an acid 

 sulphite as a reducing agent and the following method gives 



