318 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Physics. 



1. Radio-activity of Uranium. — Sir William Ceookes has 

 recently made an investigation in regard to Becquerel's rays, the 

 most important result of which is the fact that he has succeeded 

 in purifj r ing uranium salts to such an extent Chat they are photo- 

 graphically inactive. There can be no doubt, therefore, that the 

 radio-active rays are not a specific property of pure uranium, as 

 has been previously supposed. 



In the course of his experiments Crookes has tested a large 

 number of specimens of barite and witherite from various locali- 

 ties without obtaining the slightest photographic action from 

 them. He then tested every mineral in his extensive collection with 

 the result that the following were found to be active: Pitch- 

 blende, uranite, autunite, orangite, thorite, euxenite, samarskite, 

 alvite, broggerite, monazite, xenotime, arrhenite, sipylite, fergu- 

 sonite, chalcolite, hielmite. These minerals, which are arranged 

 in the order of their intensity of action, all contain either 

 uranium or thorium. Pitchblende, the most active mineral 

 showed great variations in the activity of specimens from dif- 

 ferent localities, but roughly speaking the variation was propor- 

 tional to the percentage of uranium present. A layer of pow- 

 dered pitchblende a quarter of an inch in thickness gave as strong 

 an action as one of the same material two inches thick, showing 

 that the action does not pass through much thickness of the 

 active material. The action was shown to be proportional to the 

 time of exposure. Several salts and oxides of uranium were 

 tested for their comparative activity upon the photographic plate 

 with the result that they did not show much difference. A 

 sample of metallic uranium from M. Moissan, however, showed a 

 slighter action. With the intention of using it as a standard for 

 comparison the author prepared a very pure specimen of uranium 

 nitrate by treatment wvth ether and subsequent repeated crystal- 

 lization. To his surprise this gave no action upon the sensitive 

 plate. It was then shown by a series of experiments that no 

 modification of physical or chemical conditions materially affects 

 the radio-activity of a uranium compound when, to begin with, 

 the salt experimented on possesses it ; other similar experiments 

 showed that, starting with an inactive uranium salt, nothing that 

 can be done to it will cause it to acquire activity. It was found 

 that when ordinary crystallized uranium nitrate is dissolved in 

 ether a heavy aqueous liquid separates containing uranium nitrate 

 that is much more active than that which remains dissolved in 

 the ether. Systematic recrystallization from water showed a 

 concentration of active material at the soluble end. Fractiona- 

 tion carried out by heating uranium nitrate until a certain amount 

 of basic salt was produced, proved that the active body gradually 



