156 AN EXPERIMENTAL STUDY OF RADIO-ACTIVE SUBSTANCES. 



reagents, and soon obtained results that were presented by Beciiuerel 

 to the Academy of Sciences, Paris, at a meeting held Monday, July 

 18, 1898. 



These savants showed that pitchblende contains a substance, appar- 

 ently analogous to bismuth, which emits Becquerel rays 4,000 times 

 stronger than uranium. The}^ were unable to isolate the element hav- 

 ing radiant power, but they named it ''Polonium,"" in honor of the 

 native land of ]Madame Curie. In December of the same year the lady 

 received the Gegner prize of 4,000 francs awarded her by the Academy 

 of Sciences, and later in the same month Monsieur and Madame Curie, 

 together with ]Monsieur Bcmont. director of the Municipal Laborator}'", 

 announced the discovery of a second radio-active body in pitch- 

 blonde, which they called "Radium." Since that date Madame Curie 

 and her husV)and have industriously carried on investigations, pul)lish- 

 ing their results in the Comptes rendus; and some German physicists, 

 not galhmt enough to leave the enterprising woman a clear field, have 

 announced a few minor discoveries. From these papei's we gather the 

 following facts concerning these marvelous bodies. 



As yet comparutixely little is known of the chemistry of the salts of 

 polonium, since the radio-active su])stance has not been separated from 

 its companions; on working up the mineral pitchblende the polonium 

 is found in the precipitate thrown down l)y sulfuretted hydrogen, and 

 ins()lu})le in ammonium sulfid. Solutions of polonium react like those 

 of bisnuith. being precipitated by Avater. 



The mixture of sul)stances in which radium shows its activity has 

 been more fidh' studied. The yet unknown element accompanies 

 barium in analytical separations, its chlorid is wholly soluble in water, 

 and it responds to the usual tests for barium. The spectrum of the 

 substance shows the })ands of barium, together with at least fifteen 

 other lines peculiar to radium. (Demar^ay, C. R., 129, 716, Novem- 

 ber <;. 1899.) Attempts to separate radium from barium have been 

 unsuccessful, but by fractional precipitation of the mixed chlorids 

 with alchohol a salt has been obtained having 900 times the activit}^ of 

 uranium. 



By operating on half a ton of the residues of uranium minerals, 

 Madame Curie obtained 2 kilograms of material rich in radium; with 

 this attempts were made to determine the atomic weight of radium, 

 and she found the figures 140. the atomic weight of barium being 136.4. 



The extraordinary physical properties of the rays emitted by these 

 bodies have commanded the most attention; they possess luminosity, 

 actinic and skiagraphic power, and render the air through which they 

 pass a conductor of electricity. This latter property, the one which 

 led to their discovery, is studied b}^ means of an electroscope of special 

 construction. It consists essentiall}^ of a gold leaf (or aluminum-foil) 



