576 



biologically a well-proportioned dosis of caesium behaves like the 

 radio-active elements potassium and rubidium. 



To elucidate this we undertook an ex|)eriment with preparations 

 of various origin. They were carefully purified and examined phy- 

 sically and biologically before and after the purification. 



By a physical inquiry we tried to determine the ionization-power 

 of the perfectly dry caesium-salt in a flat, air-tight ionization chamber. 

 The salt had been spread evenly on a copper dish of 30 cm. 

 diameter. 



The dish was isolated with amber and charged to constant poten- 

 tial of 500 volts by a battery of small accumulators. 3i cm. above 

 the salt layer was a copper disc also of 30 cm. diameter, which 

 was coimected with a pair of quadrants of a sensitive electi'ometer. 

 The "needle" of this electrometer was maintained at 40 volts. 



A uranium-unit of Mc Coy of 50 square m.m. showed with this 

 arrangement a detlection of 100 scale-divisions in about 2 minutes; 

 a layer of dried potassium-chlorid in 5 minutes about 50 scale- 

 divisions '). 



Our caesium-chloride prepai'ations yielded widely differing results, 

 of which a survey is best obtained by a comparison with the ioni- 

 zation power of potassium ceteris paribus. 



The biological examination was carried out with an isolated frog's 

 heart (ventricle -|- right auricle suspended to a Symes caunida with 

 an overflow, so that the pressure could never exceed 5 cm. of water. 

 Three Mariotte-flasks with a cock-system provided a means of per- 



') We see, then, that in Ihis flat ionization chamber the ionization power of 

 potassium (beta-radiator) is 7000 times weaker than that of uranium (alpha-radia- 

 tor). This ratio will be quite different in a high ionization-chamber. Rutherford 

 (p. 528) estimates the ionization power in the ordinary ionization-chamber at Viooo 

 of the beta-radioactivity of uranium. The beta-radioactivily of uranium in its turn 

 rests on uranium X, with which the uranium of the ordinary preparations is in 

 equilibrium. 



