Chemistry and Physics. 319 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Induced Radio- activity produced by Salts of Radium. — 

 An interesting series of experiments has been made by P. Curie 

 and A. Debierne, which shows that radio-activity is trans- 

 mitted in the air through short distances and induces activity in 

 other substances. This induced activity is much more intense 

 when it is produced in completely closed vessels than when the 

 action takes place in the open air. A radiferous substance was 

 placed in a small open bulb in a closed vessel, and plates of 

 various substances (lead, copper, aluminium, glass, ebonite, card, 

 paraffin, all of w T hich appear to be acted on in about the same 

 manner) were placed in various positions in the vessel, and in all 

 positions, even behind a lead screen, they became active to about 

 the same extent after a day's exposure, provided that the air of 

 the vessel had free access to their surfaces. A plate resting on 

 the bottom of the vessel became active only on its exposed sur- 

 face. With very active barium chloride (radium), plates exposed 

 for several days in this way attained an activity 8000 times 

 greater than a plate of metallic uranium of the same dimensions. 

 When exposed to the free air, the plates lose the greater part of 

 their activity in a day, but the activity disappears much more 

 slowly when the plates are left in the closed vessel after the 

 active substance has been removed. If the experiment is made 

 with the bulb containing the active substance completely closed, 

 no induced activity is obtained. Other experiments showed that 

 this induction is rapidly carried through capillary tubes connect- 

 ing small closed spaces. It was found that the action is pro- 

 gressive, finally reaching a limit which depends upon the 

 activity of the active body. The action is more rapid the 

 smaller the vessel containing the bodies. These phenomena 

 have been observed with various salts of active barium, such as 

 the chloride, sulphate, and carbonate. Salts of actinium also 

 produce induced activity, but, on the other hand, salts of 

 polonium, even when very active, produce no such effect. The 

 authors believe that this circumstance may have a connection 

 with the fact that polonium does not emit rays that are deviated 

 by the magnetic field. 



In a subsequent communication the same authors state that 

 water can be rendered radio-active either by distilling it from a 

 solution of radium chloride in an air-tight vessel, by placing a 

 dish of water in a closed space containing a solution of a radium 

 salt, or also by enclosing a solution of a radium salt in a her- 

 metically closed celluloid capsule and plunging the latter into 

 distilled water in a closed vessel. In the last case, no trace of 

 the salt passes into the water, but the activity of the solution is 

 to a great extent communicated to it. This induced activity can- 



