RADIUM. 195 



The action of radium ra,ys on nervous centers may result in paralysis 

 or death. They seem to act with particidar intensity on living tissues 

 in the process of growth." 



VIII. 



When an}^ solid body is placed near a salt of radium it acquires the 

 radiant properties of radium, or in other words becomes radio-active. 

 This induced radio-activity persists for some time after the body is 

 removed from the presence of the radium, but it becomes steadil}^ 

 feebler and diminishes about half in each half hour till it disappears. 

 This phenomenon is produced in a particularly intense and regular 

 fashion if the solid body is placed with the radium salt in a closed 

 vessel, aiid it is advantageous to emplo}' a solution of radium salt 

 rather than the salt in the solid form.* 



A salt of radium is placed at A (tig. 8) in a glass reservoir which 

 communicates by tubes t and t' with two other glass reservoirs B and 

 C, from which air may be exhausted. It may be shown that the walls 

 of the reservoirs B and C become radio-active and emit 

 Becquerel rays analogous to those emitted ordinarily b}^ 

 radium itself, while on the contrary the solution of radium 

 emits very little radiation, so that the radio-activity 

 becomes, as it w'ere, exteriorized. 



This phenomenon is well exhibited in other gases than 

 air, and is independent of the presence of the gas. The 

 radio-activity is communicated from one place to another 

 by a sort of conduction through the gas, and may even be 

 propagated from one reservoir to another through a cap- 

 illary tube. Gas which has been in contact with radium, fig. 8— induced 



•^ ^ _ _ ' radio-activity. 



therefore, ac(iuires the propert}^ of imparting radio- 

 activity to solids. The gas is itself radio-active, but does not emit 

 raj^s which are very penetrating. Rays emitted by gases are not 

 transmitted through the walls of a glass receiver. 



When the gas thus modified is removed far from the radium it retains 

 its properties for a long time, and continues to emit Becquerel ra3\s of 

 slight penetration and to impart radio-activity to solids. But its 

 activity from either point of view diminishes b}^ half in each four days 

 till it disajDpears. 



Rutherford supposes that radium continually emits a radio-active 

 gaseous substance which diffuses in space and provokes the induced 

 radio-activity. He gives to this hypothetical substance the name of 

 radium emanation and believes that it is to be found in a mixed condi- 

 tion in gases in the vicinity of radium. Without necessarily admit- 



« Danyz, C. R., Feb. 16, 1903. G. Bohn, C. R , April 27, 1903. 

 b M. and Mine. Curie, C. R., Nov. 6, 1899. Curie and Debierne, C. R., ]Mar. 4, 1901, 

 July 29, 1901, Mar. 25, 1901. 



