SIR WILLIAM CKOOKES ON SCANDIUM. 17 



a white sublimate. The mineral begins to crack at a temperature a little below 

 redness, and, at the approach of redness, gas is evolved with almost explosive violence, 

 the mineral breaking and flying about the tube. A fragment so treated examined 

 under the microscope shows a surface covered with glistening points. With a high 

 power these points are resolved into a mass of minute cubes, curiously regular in form 

 and appearance. Heating drives off 5 '8 3 per cent, of its weight ; 5 "8 2 of the loss is 

 water and acid vapour, the difference, O'Ol per cent., consists chiefly of helium, with 

 a little hydrogen, carbon dioxide, and a mere trace of neon. The average amount of 

 gas collected from 100 grs. of the mineral was 15 '6 cc. Sir JAMES DKWAR kindly 

 passed the gases for me over hot oxide of copper and then through charcoal immersed 

 in liquid air. This should absorb and retain everything but helium and the trace of 

 neon. The eas thus purified, after exhaustion to the most luminous point, was sealed 

 in a double-bulb silica tube. The spectrum, visual and photographed, was that of 

 pure helium with a scarcely perceptible trace of neon. 



Containing so many bodies, the exact separation of which one from the other is not 

 known, it is at present impossible to give an accurate and complete analysis of 

 wiikite. Moreover, I find the composition varies somewhat in different samples of the 

 mineral. The following is considered a fair approximation of the composition of a 

 typical specimen : 



Tantalic acid with some niobic acid 1 5 '9 1 



Titanic acid and zirconia 23 '36 



Earths of the cerium group 2 '5 5 



Earths of the yttrium group 7 '6 4 



Scandia 1-17 



Thoria 5 '51 



Ferrous oxide 15 '52 



Uranic oxide 3 '56 



Silica 16'98 



Water and gases 5 - 83 



Calcium, manganese, tin, sulphur, &c., unestimated . . 1'97 



100-00 



The percentage of scandia is too low. Owing to the difficulty of separating it 

 completely from the accompanying earths and metallic acids, the amount given is 

 only that which has been obtained in an approximately pure state. 



I find the following the best process to extract scandia from wiikite : The 

 ground mineral is passed through an 80-mesh sieve, then mixed with five times its 

 weight of powdered potassium bisulphate and fused in a clay crucible. At first much 

 frothing occurs, due to the escape of permanent gases and aqueous vapour ; this 

 ebullition can be abated by stirring with an iron rod. When in quiet fusion, the heat 

 is raised to full redness for ten minutes and the liquid mass poured on an iron plate. 



VOL. CCIX. A. D 



