582 MINERALOGY 



Platinum, Ft. Atomic weight, 195. Fusing point, 1755 C. 



Platinum is reduced from an ore and cupeled as described 

 under silver, p. 578. If much platinum is present, the lead button 

 will solidify before all the lead is driven off. The remaining lead 

 may be removed by treatment in O. F. beside borax on coal ; the 

 lead is oxidized and absorbed by the borax. The remaining 

 button will contain the silver, gold, and the metals of the platinum 

 group ; this is dissolved in nitro-hydrochloric acid, solid ammo- 

 nium chloride is added, and the solution evaporated nearly to 

 dryness ; it is now diluted with alcohol and the yellow ammonium 

 platinic chloride, NH 4 PtCl 6 , is filtered out, washed with alcohol, 

 carefully ignited, when the platinum will remain as sponge plati- 

 num, with other metals of the platinum group. If there was any 

 gold in the button, it will be found in the filtrate from the ammo- 

 nium platinic chloride. 



Other Metals of the Platinum Group 



Ruthenium, Ru. Atomic weight, 101.7 Fusing point, 1950 C. 



Rhodium, Rh. Atomic weight, 102.9. Fusing point, 2000 C. 



Palladium, Pd. Atomic weight, 106.7. Fusing point, 1586 C. 



Osmium, Os. Atomic weight, 190.9. Fusing point, 2500 C. 



Iridium, Ir. Atomic weight, 193.1. Fusing point, 1950 C. 



All the above five metals are rare. They are associated in 

 small quantities with some native platinum. Their separation is 

 difficult and there are no blowpipe or simple wet tests by means 

 of which small quantities may be conveniently detected in minerals. 



* 



GROUP VI 



Metals, the sulphides of which are insoluble in dilute acids, 

 but soluble in alkali sulphides. 



Common elements: gold, platinum, tin, antimony, arsenic. 



Rare elements: germanium, iridium, molybdenum, tungsten, 

 tellurium, selenium. 



Gold, Au. Atomic weight, 197.2. Fusing point, 1065 C. 



a. Gold is generally present as metallic gold, but in such fine 

 particles as not to be discernible by the eye or hand lens. It is 

 necessary to collect, or concentrate, the gold from a pound or 

 more of ore. The ore is ground to pass an 80-mesh sieve ; after all 

 the sample has been sifted, the sieve is examined for particles 



