202 Mr. W. B. Hardy and Miss E. G. Willcock. [July 21, 



Action oftJie Radiations from Badium. 



We used 5 milligrammes of pure radium bromide, supplied by 

 Buchler & Co., of Brunswick, and we found that a solution of iodoform 

 in chloroform was turned deep purple by simply resting the test-tube 

 containing it on a plate of mica covering the radium salt. That is to 

 say, the active rays penetrate mica and glass. 



They also penetrate cardboard. Tubes containing a solution of 

 iodoform in chloroform were enclosed in a box of black cardboard, and 

 they remained unchanged for 60 hours. On placing the box over the 

 radium salt the tubes became purple in about 10 minutes. 



For the following reasons we believe that the active rays from 

 radium are entirely different from the active rays of light. 



The active rays of sunlight are completely arrested by an opaque 

 layer of lamp-black deposited over a test-tube, by black cardboard, by 

 aluminium, or, in short, by any substance opaque to visible light rays. 

 The active radium rays traverse lamp-black, black cloth, or cardboard, 

 and aluminium sheet 1 mm. thick, without any measurable loss. 



An ordinary yellow gas-light was found to emit active rays in 

 quantity sufficient to change iodoform dissolved in chloroform at 1 foot 

 distant in a few minutes, even when the test-tube was jacketed with 

 water in order to prevent any heating. There is, therefore, no reason 

 to believe that the activity associated with light is different from the 

 ordinary chemical activity of light. 



The radium rays which produce the change were identified by 

 measuring the effect of screens upon the time necessary to produce a 

 standard depth of purple in 1 c.c. of a standard solution of iodoform in 

 chloroform. 



A comparison of radium unscreened and screened so as completely to 

 intercept the a rays, failed to show any action on the part of these rays. 



Attention was then turned to the more penetrating fi and y rays. 

 A corked test-tube was suspended at a constant distance from the 

 radium (approximately 3 mm.), the same test-tube being used through- 

 out. 1 c.c. of the standard solution was used for each measure- 

 ment. In these measurements the wall of the test-tube was always 

 present as a screen. 



Time necessary to read the standard colour 



Minutes. 



* In this case the distance between the radium and the solution was, of coiirse, 

 increased in order to make room for the screens. 



