THP: radio-activity of MATTi:K. 199 



only :i few volts; it should be constant and independent of the potential 

 V, luMi this is very high. Gas renjlered conducting- In' these rays retains 

 this property for some instants. Between two conductors maintained 

 at constant potentials these rays set up in ;iir a continuous current. 



These experiments were taken up and elaborated by Lord Kelvin in 

 l.S!»T, then by Messrs. Beattie and 8. do Smolan. In 189!> ^Nlr. Ruther- 

 ford showed how the phenomena due to the conductivity communicated 

 to gases by uranium, and the existence of a maximum in the current 

 produced, could he explained by the hypothesis of ionization, to which 

 the Ix'autiful work of Mr. J.J. Thomson has given the seal of authorit3% 



In ISDS M. Schmidt and Mnie. Curie observed, quite independently, 

 that thorium has properties analogous to those of uranium, properties 

 wiiich were specially examined by Mr. Owens and Mr. Rutherford. 

 Mme. Curie having measured the ionizing activity of a large numlter 

 of minerals containing uranium or thorium, announced the rt'markal)le 

 fact that several minerals wer(^ more active than metallic uranium. 

 ]Vl. and ]\Iine. Curie concluded that there nuist be a more active ))ody 

 than uranium in the mineral, and they undertook the task of isolating' it. 



By treating one of the most active of these minerals, A'iz,pitch})lende 

 from Joaciiimstal, they first separated an active l)ismuth, to which 

 they gave the name of polonium, then shortl}' afterward they obtained 

 a ver}' active l)arium containing a new element, radium. 



These ])odies are prepared hy fiactional precipitations, in which one 

 is guided l>y the indications of the electrometer; the activity of these 

 pi'oducts is 100,000 times greater than that of uranium. 



At)out the same time M. Giesel succeeded in preparing some very 

 active sul)stances, and in 1!»0() ]\I. I )ebierne announced the existence of 

 a new element, actinium, about which, however, we have not heard 

 many ])articulars. Of all these new bodies radium alone is character- 

 ized as a new element; it has an emission spectrum consisting of lines 

 which do not Ixdong to any other known l)ody, and tiie atomic w(Mght 

 of the active salts of barium was found to increase* with the })ro))ortion 

 of radium present. 



Tlie activity of uranium was not sufficient to excite phosphorescence 

 in otiier 1)odies; M. and Mme. C-uric*. however, observed this ])henoni- 

 enon with the rays from radium, and further, that the salts of radium 

 were themselves luminous, their luminosity being, like their radio- 

 activity, spontaneous. The activity of radium pi'oduces \arious 

 clicmical reactions; it colors glass, it transforms oxygen into ozone, 

 it changes white ])h<)sph()i-us to red, it ionizes not only gases but also 

 liquids, such as petroleum and li((uid air. and insulating solid bodies, 

 such as paraffin, de\('lo})ing in this latter body a residual conductivity 

 which lasts a long time after the rays have ceased to act. It also 

 causes on organic tissues sei'ious l)urns analogous to those produced 

 oy X-rays. 



