118 RADIOACTIVITY. 



tain with the well-known Balmain dyes, which become luminous 

 after exposure to the light, if results could be obtained resembling 

 those with a Rontgen tube. 



Similar attempts by the French physicist, Henri Becquerel, w^ere 

 crowned with success in an unexpected direction. He exposed a 

 uranium salt to the light, and then placing it in a dark room on a 

 photographic plate covered with opaque paper he demonstrated the 

 action of these rays on the plate through the paper, thin sheets of 

 metal, etc. But the supposed and sought-for relation of the rays to 

 the previous fluorescence was not evident, for Becquerel obtained pre- 

 cisely the same results with preparations of uranium which had not 

 only not been previously exposed directly to the light but had pur- 

 posely been kept sometime in darkness and could therefore display no 

 stored-up luminescence. He had, however, discovered the uranium 

 or Becquerel rays. Prof. C. C. Schmidt, in Erlangen, afterwards 

 obtained similar results by experiments with thorium and its com- 

 pounds, and thus became the discoverer of the thorium rays. 



At Becquerel's suggestion Madame Curie undertook a systematic 

 investigation of all the chemical elements and established the fact 

 that with none of them, excepting uranium and thorium, could an 

 appreciable effect indicating rays be obtained with her apparatus. 

 On the other hand, she found that many of the minerals investigated 

 showed noticeable action in this direction. The fact that a few of 

 them, the uranium iDitchblende, for example, from Joachimsthal, 

 Bohemia, emitted rays three or four times stronger than those of 

 pure uranium, and which could not therefore be announced as 

 uranium rays, led her to suppose that in the pitchblende itself, apart 

 from the uranium, there must exist a still more powerful radioactive 

 substance. It is a matter of record how, in this research, which 

 might serve as a model for such work, she and her husband, so soon 

 afterwards to lose his life by a deplorable accident, succeeded in 

 tracing this supposed substance more and more accurately, and finally 

 in obtaining it pure. Madame Curie thus became the discoverer of 

 radium, a new element possessed of wonderful, of fabulous qualities. 



Besides Madame Curie no other investigator but Professor 

 Braunschweig, so far as I know, has yet succeeded in obtaining pure 

 radium. The difficulty of conducting this research will be appre- 

 ciated wdien I refer to the fact that out of a carload of pitchblende 

 from Joachimsthal, the most rich in radium of any material so far 

 known, Madame Curie secured in all but one-fourth of a gram of 

 radium chloride. Out of a mass of 1,000 kilograms to secure its 

 four-millionth part, in a substance evenly diffused through it, is a 

 record of chemical analysis which surpasses a hundredfold all pre- 

 vious work of the kind, and success in this attempt became possible 



