236 O. S. Ptihnan — Determination of Uraninm and 



natural inference to be drawn is, that when an uranium sul- 

 phate solution is reduced with zinc and sulphuric acid out of 

 contact with the air, a compound of uranium lower than that 

 corresponding to the uranous condition may be formed. Zim- 

 mermann* opposed this view, but his mode of operation would 

 give this very unstable body the chance to be oxidized back to 

 the uranous condition before coming in contact with the per- 

 manganate. His method was to pour through the air his 

 reduced solution into an excess of permanganate previously 

 diluted and acidulated, then to destroy this excess by a slight 

 excess of ferrous sulphate, and to titrate the excess of ferrous 

 sulphate with more permanganate. Zimmermann, further- 

 more, in reducing his solution in a small flask, w^ith a compara- 

 tively small amount of zinc, did not give the uranyl salt as 

 great a chance to be reduced below the uranous stage as is given 

 by the greater exposure of zinc surface when the solution 

 passes through the reductor. As has been shown in the table, 

 the results do not run together constantly for the same amounts 

 of uranium used, and it appears that the amount of lower oxide 

 formed depends upon the manner of action upon tbe zinc, and 

 that it is so unstable that the least trace of oxygen may change 

 it very materially. In fact, when the olive-green solution is 

 poured through the air, the change to the sea-green color of 

 the uranous salt is immediate. 



The results establish pretty conclusively that it is not advis- 

 able to pass the solution through the reductor into a flask full 

 of carbon dioxide. This would appear to be what Kern tried 

 to do by dropping his solution into a funnel, and so into his 

 " titration flask," but during this operation the solution must 

 have been exposed to the air enough to oxidize the lower oxide 

 to the uranous state (Kern thought that the uranyl sulphate 

 was not reduced below uranous sulphate by passing through 

 the reductor), and the protection offered afterward by the car- 

 bon dioxide generated from a gram of sodium carbonate would 

 hardly be significant. The conditions under which Kern oper- 

 ated could not be repeated exactly, since the uranium sulphate 

 would not, without suction, pass through a reductor consisting 

 of an 18-inch column of 2()-mesh amalgamated zinc set up 

 according to directions, in less than five times as long a period 

 as Kern's table called for. When operating, however, as nearly 

 as possible according to Kern's prescription, that is, by gentle 

 suction into a flask, no carbon dioxide was needed. In fact, as 

 previously stated, high results were obtained. In thinking it 

 necessary to have carbon dioxide present because Zimmermann 

 poured his reduced uranium solution directly into permanga- 

 *Ann. Chem. (Liebig), ccxiii, 302-304. 



