104 On the Action of 



muriate of platina is among the most soluble salts. Thtf 

 best method of presenting the three solutions of platina, 

 silver, and green sulphate of iron to each other, is first to 

 pour the filtered solution of the last into the solution of 

 platina, and then, after mixing them thoroughly together, 

 to add the solution of silver by degrees, and to stir them 

 constantly. In this, as in all similar operations, the pre- 

 sence of all acids, salts, &c. excepting those necessary for 

 the operation, should be avoided ; and if proper proportions 

 have been used, and all circumstances attended to, the pre- 

 cipitation of these two metals will be very complete. 



But the precipitation by a solution of mercury requires 

 to be further considered, as the state of oxidizement of this 

 metal, as well as the acid in which it is dissolved, produces 

 a considerable modification in the result. In the first place, 

 the oxide, at the minimum of oxidizement, dissolved in 

 muriatic acid, is unfit for the experiment ; and even the red 

 oxide dissolved in the same acid, or corrosive sublimate,is not 

 the most advantageous. When a warm solution of the latter 

 is poured into a mixed solution of platina and green sulphate 

 of iron also warm, as in the case of silver, these substances 

 are brought into contact under the most favourable circum- 

 stances. Yet even thus the precipitation is slowly and im- 

 perfectly formed, often not till several hours have elapsed j 

 and sometimes a very great deficiency of weight is observed 

 between the quantities used and those recovered directly by 

 this method. If a solution of nitrate of mercury be used, 

 the effect is produced more rapidly, and the precipitate is 

 more abundant. The precipitation of muriate of platina by 

 nitrate of silver, and the combination which ensues from it, 

 suggested to me an experiment which I must state at length, 

 as from the result of it consequences are deduced which 

 modify some of the experiments of ray former paper. 



It occurred to me that a method of uniting platina and 

 mercury without the intervention of any other metal, or of 

 any substance but the solvents of these metals, might be 

 accomplished as in the case of silver and platina. I there- 

 fore poured a solution of nitrate of mercury, which solu- 

 tion, being at the minimum of oxidizement, consequently 

 formed an insoluble muriate with muriatic acid, into a so- 

 lution of muriate of platina. The result was a triple salt 

 of platina and mercury, which, when the mercury was com- 

 pletely and totally at the niinimum of oxidizement, was 

 nearly insoluble. To procure it in this state it is sufficient 

 to put more metallic mercury into dilute nitric acid than the 

 nitric acid can dissolve, and to boil them together. This 



triple 



