348 W. Gihbs on the Platinum metals. 



soda and tlien reducing the iridium to sesquichlorid by cautiously 

 adding a very dilute solution of nitrite of soda. 



In the second place it may happen, as in working with crude 

 platinum solutions obtained, not from osmiridium, but from pla- 

 tinum ores, that the quantity of platinum is very large when 

 compared with that of iridium. The process applies equally 

 well to this case so far as the iridium is concerned, but it is dif- 

 ficult and troublesome to recrystallize large quantities of a salt so 

 insoluble as the chlorplatinate of potassium, PtOl2,KCl, and small 

 quantities of the corresponding iridium salt are dif&cult to re- 

 move. A method of obtaining platinum in a state of chemical 

 purity will be given further on. 



The above process is capable of giving chemically pure iridium 

 when platinum is the only other metal present. This is rarely 

 the case and the following method is usually more advantageous. 

 The greater part of the platinum is first to be separated in the 

 manner above pointed out. The solution of double chlorid ot 

 iridium and sodium, Irj,Cl3,3NaCl, is then to be filtered, an ex- 

 cess of nitrite of soda added and the solution boiled until it 

 assumes a clear orange-yellow color. To the boiling solution 

 sulphid of sodium is to be added drop by drop as long as this 

 produces a cloudiness and until a small quantity of the precipi- 

 tated sulphid of platinum, PtS^, is redissolved. Dilute chlorhy- 

 dric acid is then to be added cautiouslv until the liquid, previously 

 allowed to become cold, is distinctly "though faintly acid, when it 

 is to be filtered and the sulphid of platinum on the filter washea 

 continuously with hot water. The filtrate is then to be boiled 

 with chlorhydric acid in excess, and the resulting chloro-indate 

 of sodium evaporated, precipitated by a cold and strong solution 

 of chlorid of ammonium, and washed with the same. This sa t 

 on ignition yields pure iridium, if the operation has been wei 

 conducted. It is in all cases however well, after separating tue 

 sulphid of platinum by filtration, to neutralize the filtrate witQ 

 carbonate of soda, boil a second time with a little additional 

 nitrite of soda and then add sulphid of sodium and proceed as 

 before. In this manner every trace of platinum is removed ana 

 the resulting iridium salt is chemically pure. , , 



Platinum from ruthe^iium.—Raihenmm in the form of bicWO" 

 rid may be approximately separated from platinum by precipi- 

 tating the two metals together in the form of PtCl„KOl, ana 

 RuOl^KCl, and washing out the ruthenium salt with cold water 

 in which it is readily soluble. The mixed solutions should oe 

 evaporated to dryness with an excess of the alkaline chlorid ana 

 the dry mass rubbed to fine powder in a mortar, after wbicn 

 almost the whole of the ruthenium may be washed ont^'^^J^ 

 water or with a cold and moderatelv strong solution ofGhion 

 of potassium. Tbe undissolved platinum salt may then be pn" 



