400 Lea — Platinochlorides and Platinum Subchloride. 



satisfactory results. In a flask is placed 300" of water, 24 

 grams of potassium platinic chloride, 12 grams each of potas- 

 sium acid sulphite and potassium chloride. Sodium acid sul- 

 phite should not be used. The introduction of sodium salts 

 interferes with the crystallization ; not indeed with the first 

 crop of crystals, but later. These are made to boil rapidly 

 together for twenty-five minutes, reckoned from the time when 

 actual boiling begins. The solution is allowed to cool, filtered 

 if necessary and placed in a large flat bottomed glass or porce- 

 lain vessel. In a day or two the red salt will commence to 

 form large crystals. The addition of the potassium chloride 

 causes the red salt to crystallize out first. 



It has seemed worth while to give these methods in some 

 detail because the red platinum salt is likely to find a con- 

 stantly increasing use in photography not only for platinum 

 printing but as a substitute for gold in toning. There is no 

 doubt that platinum is a much better metal for toning silver 

 prints than gold. Its tones are better and its action is much 

 more reliable. 



By all these methods this beautiful salt is obtained in fine 

 ruby red prisms. 



Probable Existence of a Platinum Subchloride. 



If in obtaining potassium platinochloride with the aid of a 

 hypophosphite in excess, the heat is continued after complete 

 conversion to the red salt, the solution in a few minutes 

 changes from red to dark brown. The substance which gives 

 the solution this dark brown color exhibits the following prop- 

 erties. 



It is very deliquescent and cannot be crystallized. There is 

 no satisfactory method of separating it from the other sub- 

 stances in solution. An oxid of platinum appears to be pre- 

 cipitated by the addition of potash and this precipitate when 

 freshly made dissolves easily in hydrochloric acid, but if it is 

 thrown on a filter and washed, almost the whole of it runs 

 through. This difficulty it is true can be avoided by washing 

 with a dilute solution of potassium chloride. But the precipi- 

 tate after washing is no longer soluble in hydrochloric acid, 

 except that the acid dissolves out a little protoxid derived 

 from the red salt, some of which is apt to escape reduction. 



The brown solution exhibits the following reactions. 



Hydrochloric acid has no effect. 



Nitric acid decolorizes it. 



Potash produces -a brown precipitate soluble in an excess of 

 the precipitant. 



Ammonia a brown precipitate insoluble in an excess. 



