192 URANIN1TE. 



consists in reducing the chromic acid to the state of 

 sesquioxide of chromium by means of oxalic acid, 

 and in determining the quantity of carbonic acid pro- 

 duced. 



This may be effected in the same way as the testing 

 of manganese-ores in an apparatus (Fig. 20) arranged 

 for the quantitative determination of carbonic acid, the 

 weighed chromate of lead being mixed with oxalate of 

 potassa, and sulphuric acid allowed to flow upon it. 

 10 parts by weight of carbonic acid indicate 7.6 parts of 

 chromic acid, or 24.5 of pure chromate of lead. Hence, 

 100 parts of pure chrome-yellow should give 40.4 of 

 carbonic acid. 



104. URANINITE. 



UO,U 2 3 > 



(together with various extraneous substances, in varia- 

 ble quantities, including silica, iron, nickel, cobalt, zinc, 

 copper, bismuth, lead, manganese, arsenic, antimony, 

 sulphur, lime, and manganese ; sometimes also selenium 

 and vanadium). 



PREPARATION OF PURE SESQUIOXIDE OF URANIUM. 

 The finely-powdered ore is digested with moderately 

 dilute sulphuric acid, with gradual addition of nitric 

 acid, until it is converted into a white powder, and 

 partly dissolved. The greater excess of sulphuric acid 

 is then evaporated, the mass digested with much water, 

 and the cold solution, after subsidence of the residue, 

 filtered off. 



The residue consists of silica, sulphate of lead and 

 basic sulphate and arsenate of bismuth. 



The solution is then heated to about 60, and sul- 

 phuretted hydrogen-gas passed through it, at this 

 temperature, for some time; the solution is afterwards 

 allowed to cool while the gas is still passing, and, when 



