INACTIVE THORIUM.* 



FRITZ ZERBAN, PH.D.. (CARNEGIE RESEARCH ASSISTANT). 



It was soon after the discovery of the well-known X-ra} r s 

 bv Roentgen, that Becquerel, in Paris, observed that remark- 

 able property of Uranium potassium sulphate by which it 

 affected the photographic plate through light-tight black 

 paper, when the sun shone on the salt. At first he thought 

 that this action was brought about by the fluorescence of the 

 Uranium salt, but very soon discovered that nonfluoresceut 

 Uranium compounds and the metal itself effected the same 

 action, and that the concurrence of the sun's rays was not 

 necessary,, the aforementioned phenomenon appearing also in 

 a thoroughly dark room. He called this peculiar property of 

 the Uranium "radioactivity", and for the rays, which produce 

 the blackening of the photographic plate, the name of "Bec- 

 querel rays" was adopted. It was shown then that the Uran- 

 ium compounds had still another remarkable property, namely 

 of diminishing the conductivity of the air for electricity, so 

 that a charged electroscope loses its charge more rapidly than 

 usual, if a Uranium compound is brought near it. Thirdly, 

 the Becquerel rays excite, like the X-rays, the fluorescence of 

 a Barium platinocyanide screen. 



Three methods for testing the radioactivity of bodies were 

 thus acquired and different investigators discovered, besides 

 the Uranium, some other radioactive substances. Mr. and 

 Mrs. Curie found in Pitchblende two such bodies; Polonium, 

 which is similar to Bismuth, and Radium, which soon brought 

 to its discoverers great fame all over the world. The Radium 

 occurs with Barium, and is separated from it by very laborious 

 and protracted operations. As Radium is the most strongly 



* Read before the North Carolina Academy of Science, Wake Forest Meeting, 

 May 14th, 1904. 



