AN experimp:ntal study of radioactive 



SUBSTANCES.' 



By Hexky Cakrixgtox Bolton. 



Professor Rontgen's remarkable discovery, in 1895, of tlie penetrat- 

 ing" rays called by him X-ra?s, but jiow equally well known by his 

 own name, was followed in 1S96 by BecquerePs discoyerv that the salts 

 of uranium emit inyisible radiations capable of discharging electritied 

 bodies and of producing skiagraphic images on sensitive plates. He 

 found that potassio-uranic sulfate emits rays that pass through }>lack 

 paper and aii'ect photographic plates. This property is not limited to 

 the brilliantly fluorescent uranic salts, but is shared by the nonfluor- 

 escent uranous salts. All uranium compounds examined proved to be 

 active, whether phosphorescent or not, whether crystalline, melted, or 

 in solution; and metallic uranium exhibits the phenomenon in a marked 

 degree. The permanence of this property is amazing, substances kept 

 in a double leaden box more than three years emitted rays having 

 almost as much power as when first tested. 



Short!}" after the announcement by Becquerel, experimenters found 

 that other substances have the power of emitting these ""Becquerel 

 rays." Henry found it in phosphorescent zinc sulfid, Niewenglowski 

 in insolatcnl calcium sultid, Troost in artificial hexagonal ])lende, and 

 Schmidt in thorium compounds. In 1898 Madame Sklodowska Curie, 

 working in the laboratory of the Municipal School of Industrial Physics 

 and Chemistry in Paris, devised a special apparatus for measuring the 

 electrical conductivity of the air when under the influence of ''radio- 

 active bodies," and by its means studied the behavior of the minerals 

 ])itch])lende, chalcolite, autunite, cleveite, monazite, orangeite. and 

 thorite, and found them all active. Some varieties of pitchblende 

 showed more than three times as much energy as metallic uranium 

 itself, and this led her to the conclusion that the peculiar property 

 was due to some unknown body contained in the mineral, and not to 

 uranium compounds. Associating her hus})and with her, Madame 

 and Monsieur Curie attacked the mineral pitchblende with acids and 



^Read at a meeting of the Cheiineal Society of Wai^hington held Ajiril 21, UR>0, at 

 Bahimore, Md. 



155 



