Uranyl Phosphate hy the Zinc Rediictor. 237 



nate in a few experimeuts, to avoid exposure to the air, Kern 

 undoubtedly misunderstood Zimmermann, since the latter ordi- 

 narily emptied bis reduced solution into a porcelain dish, 

 diluted it with water, and then titrated it with permanganate. 

 Zimmermann did try some experiments, as previously described, 

 by pouring the reduced solution directly into an excess of per- 

 manganate, but that was only in the few cases when he was 

 trying to prove that the uranyl salt was not reduced below the 

 uranous condition by zinc and sulphuric acid. Ordinarily, 

 however, Zimmermann's operation was not conducted in that 

 way. 



It would appear, therefore, that Kern labored under a mis- 

 apprehension in regard to the use of carbon dioxide in his 

 " titration flask," that the zinc employed in his own work must 

 have been larger than that which is called for in his directions 

 for setting up the reductor, and that his statement is wrong 

 that uranyl sulphate is not reduced below the uranous condition 

 of oxidation by passing through a long Jones reductor made 

 as above described. 



After completing these experiments with carbon dioxide, a 

 few trials were made to see whether, by running air through 

 the solutions reduced in the ordinary way as worked out for 

 the determination of uranium, the solutions would be oxidized 

 above the stage represented by UO^. It was found that by 

 bubbling air rapidly through the solution for ten minutes it 

 was oxidized to an amount equal to about 0*0020 gram of UOg 

 for 01336 gram UO3 used. 



The process, then, for the determination of uranium by the 

 reductor depends upon the fact that any reduction of uranium 

 lower than uranous oxide — and such reduction undoubtedly 

 takes place in the reductor — is corrected by exposure to the 

 air, the lower oxide being rapidly oxidized to exactly the ura- 

 nous state, while the uranous salts are stable enough to permit 

 of being estimated before they are oxidized. 



Kern also stated, in the same article, that the filtering of a 

 precipitate of ammonium uranyl phosphate through a Gooch 

 crucible could not be accomplished on account of the fineness 

 of the precipitate. In trying to work out a method for deter- 

 mining phosphoric acid by precipitating the phosphoric acid in 

 the presence of ammonium salts by uranium, filtering off the 

 ammonium uranyl phosphate thus obtained, determining the 

 uranium in the precipitate according to the method just 

 described, and then, from the amount of uranium so found, 

 estimating the phosphoric present, much experience was 

 obtained in filtering off the precipitate, which, as Kern said, is 

 very finely divided and tends to pass through the filter very 

 easily. It was found that the precipitate went through two 



