416 



Sir W. Crookes. 



of the substance. On an ordinary microscopic slide I put a small 

 drop of liquid from each of the highest five fractionations, Nos. 10, 9, 

 S, 7, and 6. The drops were allowed to crystallise and the slide was 

 aid on a sensitive plate. In twenty-four hours a good impression of 

 1^0. 10, the highest fraction, was obtained; a less strong impression 

 of the next, No. 9 ; a fainter one of 8 ; a scarcely perceptible one 

 of 7 j and no impression at all from No. 6. The slide containing the 

 five crystalline spots was then covered with another glass, and the 

 whole cemented together with Canada balsam and mounted in the 

 manner usual with microscopic slides. When the balsam was dry the 

 slide was put on a sensitive plate. In twenty-four hours a good 

 graduated image was developed. 



19. There are in commerce two kinds of uranium nitrate : one, the 

 commercial variety, and another called " purissimum." I am informed 

 that the "purissimum" is prepared from the former by repeated 

 crystallisation. I purchased some of each of these nitrates and tested 

 them on a photographic plate. The commercial variety proved to be 

 at least twice as radio-active as the " purissimum " salt. 



, 20. Experiments were now instituted with a view of obtaining a 

 wholly inactive uranium nitrate. About two pounds of the " salt that 

 had been obtained from the solution in ether was repeatedly crystal- 

 lised, pouring olf the mother-liquor each time. This and the next 

 succeeding two lots of crystals (Nos. 1, 2, and 3) were put into cells, 

 and kept on a sensitive plate for seven days. On developing the 

 plate no image could be detected where No. 1 had been ; a scarcely 

 perceptible impression could be just detected at No. 2, and a little 

 stronger impression at No. 3. 



21. Other methods were attempted for the separation of the active 

 substance from uranium. Uranium nitrate fuses at a moderate 

 temperature, and after some time it becomes darker, and nitrous 

 fumes come off. Finally, the mass becomes semi-fluid, and will not 

 run. The operation is then stopped, and the mass transferred to 

 water ; the undecomposed nitrate is dissolved out, leaving an insoluble 

 basic nitrate. The basic nitrate is of an orange-yellow colour, easily 

 dissolved in nitric acid to again form the normal nitrate. By using 

 this , method of fractionation the active body gradually accumulates 

 towards the basic end. But the method is neither so complete nor so 

 easily efi'ected as the crystallisation method, and therefore I have not 

 pushed it very far. I have, however, proved that the radio-activity of 

 nitrate of uranium can be concentrated by fractionation to the basic 

 nitrate end, the nitrate at the other end being diminished in radio- 

 activity. 



, 22. A highly active uranium nitrate, prepared by fractionation 

 from the part insoluble in ether, was dissolved in water, and ammonia 

 in excess was added. Yellow ammonium uranate was precipitated. 



