320 POPULAR SCIENCE MONTHLY. 



titanium series. They have not been separated perfectly from their 

 analogues, and consequently their chemical properties and the actual 

 intensity of their physical activities is very imperfectly known. The 

 difficulties of securing even small quantities of crude materials are 

 enormous; Fritz Giesel obtained from one thousand kilograms of raw 

 material only fifteen grams of active compounds, and Mme. Curie, 

 operating on half a ton of the residues of uranium from a chemical 

 manufactory, got about two kilograms of barium chlorid rich in radium, 

 but the percentage of active substances in these mixtures is unknown. 



Eadium is spontaneously luminous, and all the bodies emit rays 

 that excite phosphorescence in gems, fmorite and other minerals; they 

 communicate radiant energy to inactive substances, and they exert 

 chemical action, transforming oxygen into ozone and producing changes 

 in the color of glass and of barium platino-cyanid. 



Through the enterprise and liberality of the Smithsonian Institu- 

 tion, and by the courtesy of Professor Langley, I have enjoyed the 

 opportunity of studying small specimens of these rare and costly sub- 

 stances; they comprised ten grams of 'radio-active substance' prepared 

 by a manufacturing chemist of Germany and smaller quantities of 

 'radium' and of 'polonium' from Paris. On removing the wrappings 

 of the German specimens in a dark room, they were seen to emit 

 greenish-white light that gave to the enveloping papers a peculiar glow, 

 similar to the fluorescence produced by Eontgen rays. Simple tests 

 of the radium showed that it gave the usual reactions of barium; on 

 boiling it with water it lost its luminosity, but on heating to dull redness 

 this property returned in the dark. It also caused a barium platino- 

 cyanid screen to fluoresce. 



Experiments to test the actinic power of these bodies gave inter- 

 esting results; on exposing sections of photographic plates, at distances 

 of five inches, from two to twelve minutes, bands were obtained varying 

 in intensity with the duration of action. By exposing sensitive plates 

 behind negatives to the radiant materials from two to three hours, 

 excellent transparencies were secured; on substituting Eastman's bro- 

 mide paper good prints were obtained. 



The penetrating power of the rays emitted permits the production 

 of skiagraphs; the plates were enveloped in Carbutt's black paper 

 (impermeable to light), and on them were laid pieces of tinfoil cut in 

 openwork pattern; after one hour's exposure negatives were secured 

 plainly showing the pattern. Analogous experiments were carried on 

 with the specimens from Paris, but they were only one fifth as strong 

 in effects; that labelled 'polonium sub-nitrate' had positively no action 

 on the plates used. 



The primary source of the energy manifested by these extraordinary 

 substances has greatly puzzled physicists, and as yet remains a mystery: 



