PLATINUM RESIDUES. 125 



to cool. The lead button formed is freed from slag, 

 and dissolved in moderately strong hot nitric acid. 

 The platinum metals remain in the state of a black 

 powder, and as grains and scales. They are then 

 treated as above. 



In the lead solution which may contain palladium, 

 the lead is precipitated by sulphuric acid. It is then 

 evaporated to dryness, the mass again dissolved in a 

 little water, and the palladium precipitated by cyanide 

 of mercury. 



Another good flux for this operation, which attacks 

 the crucible less, is a mixture of fluorspar and an- 

 hydrous gypsum of equal equivalent weights (I pt. 

 CaF, and 1.7 pt. CaO, So 3 ), 1 pt. of platinum residue, 

 1 pt. granulated lead, and 2 pts. of flux. 



3. The platinum residue is fused with an equal 

 weight of caustic potassa and twice its weight of nitrate 

 of potassa, in an iron crucible, finally heated to redness 

 with frequent stirring. The mass is poured out, coarsely 

 powdered, hot water added, mixed with one-tenth al- 

 cohol, and boiled until completely decomposed. By 

 this means the esmate of potassa is changed to osmite, 

 the ruthenite of potassa completely decomposed with 

 separation of black oxide of ruthenium. The washed 

 black residue is mixed with the liquid from the coarse 

 heavy grains and scales not acted upon, which are 

 fused for the second and third time with potassa and 

 nitrate of potassa, until at last only oxide of iron re- 

 mains. 



The clear alkaline solution from the osmate of 

 potassa is drained off by means of a syphon from the 

 black residue, and this again washed with hot water 

 containing alcohol. The black mass, which still con- 

 tains much osmium, is placed in a tubulated retort, 

 with a funnel tube, and to this a receiver is placed, 

 which, with large quantities, is united to some Woulfe's 

 bottles bv large tubes filled with a mixture of alcohol 



