a, y8 AND y RAYS 



159 



a gold-leaf electroscope. Fig. 40 represents the type of electro- 

 scope used by Soddy. It consists of a tin can with a movable 

 bottom E for the insertion ol' the substance to be tested. A 

 paraffined rubber cork, H, is pierced in the centre by the metal 

 wire, G, which carries at its end a rod of fused quartz, A. A thin 

 brass strip, B, to which a single gold leaf, C, is attached, is fastened 

 to the lower end of the quartz rod. F is a vulcanite handle by 

 means of which the charging rod, D, can be brought into contact 

 with B. The rate of collapse of the gold leaf may be observed by 

 means of a reading microscope through a window in the can 

 (dotted line). 



In 1903, the Curies, who were examining the minerals containing 

 uranium, discovered a new element, 

 radium, in pitchblende. This very radio- 

 active material was obtained pure in 1911. 

 From a ton of pitchblende may be ex- 

 tracted about 200 mgrms. of radium 

 chloride, which w^as responsible for over 

 80 per cent, of the radio-activity of the 

 raw material. 



Subsequent investigations by the above 

 workers, and principally by Rutherford, 

 Soddy, and their collaborators, have shown 

 that there are three series of radio-acti\'e 

 elements. The appended chart from Soddy 

 show^s the relationship between the mem- 

 bers of the series and betw'een two of the 

 series themselves. This chart demon- 

 strates to us the remarkable fact that 

 the atom of the heavy elements at the 

 head of each series is continuously and 

 regularly undergoing disintegration. Matter and energy are being 

 lost at a rate which, so far, cannot be modified in any way. 



Lately Campbell and Wood have discovered that certain of the 

 elements of low atomic weight are also radio-active. One of 

 these, potassium, is found universally and in abundant quantities 

 in animal and vegetable cells. Potassium is a necessary per- 

 manent constituent of every living cell. Of the 12-15 elements 

 essential to life, it is the only one possessing distinct if minute 

 radio-activity. The activity of potassium may readily be demon- 

 strated by means of the gold leaf electroscope. It is shown that 

 13 rays are emitted. Potassium is 1,000 times weaker than uranium 

 and 1,000,000,000 times weaker than radium in the emission of 

 13 rays. 



Fig. 40. — Section tlirough gold- 

 leaf electroscope as used to deter- 

 mine the ionising power of radio- 

 active matter. See text. (From 

 Soddy's Radioactivity. Electrician 

 Press.) 



