Badio-adivity of Uranium. 



415 



On development it was found that the action of the part undis- 

 solved by ether was very strong, that of the original nitrate not more 

 than half as strong, while no action whatever could be detected on the 

 part of the plate covered by the salt soluble in ether. 



The portion insoluble in ether, after evaporation to dryness with 

 nitric acid, and then crystallisation in water, in no way differed in 

 appearance from ordinary uranium nitrate. The portion soluble in 

 ether, when dried, heated with dilute nitric acid and crystallised, also 

 had the same appearance as the initial salt. 



14. The crystallised nitrate from the portion insoluble in ether I 

 again extracted with ether. Most of it dissolved, and a small portion; 

 of heavy aqueous liquid settled at the bottom. As before, the nitrate 

 which dissolved in ether had scarcely any radio-active power, while 

 the residue from this second extraction possessed it in a strong degree. 

 The residue after the second extraction was about double the activity 

 of the residue after the first extraction, showing that ether, while 

 dissolving uranium nitrate itself with facility, does not dissolve the 

 body to which it owes its radio-activity. 



15. The uranium nitrate from the portion insoluble in ether was 

 submitted to fractional crystallisation in the following manner : — 



The solution was evaporated until on cooling about three-fourths 

 would crystallise out. The beaker in which this operation was per- 

 formed was called No. 1. When crystallisation had finished, the 

 mother-liquor was poured into a beaker called No. 2. A little water 

 was added to No. 1 and it was warmed to dissolve the crystals ; No. 2 

 was evaporated a little, and both were set aside to crystallise. "When 

 cold the mother-liquor from 2 was poured into a beaker No. 3, the 

 mother-liquor from 1 was poured into 2, a little water being added to 

 dissolve the crystals in 1, and the contents of the three beakers were 

 warmed and allowed again to crystallise separately. This operation 

 was continued as long as the uranium salt would hold out, or till the 

 tests showed that the operations had gone far enough. 



16. Tests were made to see how the operations were proceeding. 

 A portion of the crystals from No. 1 beaker was dried and put into, 

 a cell. Some mother-liquor from the last beaker was also evaporated 

 and crystallised, and the crystals were put in a cell. The two were 

 placed side by side on a sensitive plate and the action was allowed tO' 

 proceed for twenty-four hours. On development there was no- 

 visible spot beneath No. 1 nitrate, while that beneath the nitrate 

 from the other end of the fractionation was strong and black. 



17. The crystals were removed from their cells, ignited to the 

 green oxide, and replaced. Tested again on a sensitive plate the 

 results were similar to those given by the unignited nitrates. The 

 active substance, therefore, is seen to reside in the mother-liquor. 



18. In making photographic tests it is not necessary to take much 



