Radium. 45 



came away a very active substance which they named polonium, 

 and with the barium another intensely active substance, which 

 they called radium. 



A third highly radio-active substance was discovered in pitch- 

 blende by M. Debierne, and called by him actinium ; it accompanies 

 certain bodies of the iron group, and is a near neighbour of 

 thorium. All these radio-active substances occur in pitchblende 

 in absolutely infinitesimal quantities. A ton of the uranium residue 

 — that is the dross of the pitchblende after the uranium is 

 extracted — yields about two or three grains of radium salt. The 

 radiation from radium is extraordinarily intense — it emits constantly 

 all the different rays produced in a vacuum tube — and a specimen 

 of a pure radium is more than one million times as active as an 

 equal weight of uranium. A few centigrams of radium bromide 

 discharge an electroscope four or five metres distant, and one can 

 easily discharge an electroscope through a screen of lead or glass 

 three inches thick. Photographic plates placed near radium are 

 almost instantly fogged. Radium can be used like X-rays for the 

 production of radiographs. 



Rutherford, Becquerel, and others have shown that radium 

 radiations comprise three different classes of rays. (1) The 

 "Alpha" rays, formed of material particles, atomic in size, charged 

 positively, thrown off with a velocity about one-tenth that of light, 

 easily absorbed by thin sheets of aluminium foil, or by a few 

 millimetres of air. About 90 per cent, of the discharging effect is 

 due to those rays. They resemble the canal rays of Golstein, but 

 have much greater velocity. According to Rutherford, these 

 resemble closely helium. (2) The " Beta " rays, absolutely 

 analogous to Cathode rays, are swarms of flying corpuscles, 

 strongly active and much more penetrative than the Cathode rays 

 of our tubes, moving with enormous velocities, many as fast 

 as light. (3) The " Gamma " rays, not deflected by a magnet, 

 traversing thick sheets of lead, are generally believed to be 

 etherical pulses of the Rontgen ray type. 



Radium radiation has an intense physiological effect, producing 



