1909] on Problems of Helium and Radium. 733 



correct value was found subsequently to be 270 c.cm. This would 

 give an increment of 0*499 c.mm., which must be taken as the 

 true value obtained from this experiment. 



The determination of the rate of production of helium made after 

 a long period of storage was carried out as a confirmatory experiment. 

 Fig. 5 shows the general arrangements of tlie apparatus used for this 

 determination. A is the 1-grm. charcoal U-tube, D the 15-grm. ex- 

 hausting charcoal bulb ; the Ra^ bottle is shown at C. This is 

 similar to that employed in the shorter period determination, with the 

 exception of a special vacuum-tight joint at B. This joint was so 

 constructed that after thoroughly exhausting the gauge, etc., the 

 drawm-out neck of the radium bulb could be broken off, thus allowing 

 the pressure of the accumulated helium from the radium in the bulb 

 to be rapidly determined. Just previous to such breaking the 

 1-grm. charcoal U-tube was placed in liquid air, in which it remained 

 during all the subsequent operations. The amount of helium pro- 

 duced from 70 m.grm. of radium chloride during nine months was 

 thus measured, and gave a pressure of 0'016;) mm., which is equi- 

 valent to a uniform rate of production of 0'-163 c.mm. of helium 

 per gramme of radium per day. The experiment was now con- 

 tinued for some five weeks on the lines of the former determina- 

 tions, observations of pressure being made daily to observe the rate 

 of production of helium from the radium while thus connected with 

 the gauge and cooled charcoal. 



At w^eekly intervals the radium was heated, and a rise of pressure 

 was recorded. Betw^een the times of heating, the pressure fluctuated 

 somewhat, but in general only gave evidence of rising. Through the 

 " heated " observations, which were six in number, the nearest straight 

 line was drawn, as in the earlier experiments. The calculated incre- 

 ment so obtained, however, had a value as high as 1*26 c.mm. of 

 helium per gramme of radium per day. This high value is untenable, 

 and is explained by the action of the radium emanation on the surface 

 of the vaselined rubber joint producing hydrogen, which would 

 remain uncondensed by the cooled charcoal. 



Thus we have • 499 c.mm. as the value of the helium produced 

 from the short-period experiments, and from the long period deter- 

 minations the value 0*463 is obtained. The actual value is most 

 probably between these two figures. 



I am not aware of any previous direct measurements of the rate of 

 production of helium from radium, but in a paper on " Some Properties 

 of Radium Emanation," by A. J. Cameron and Sir William Ramsay,* 

 the ratio of the amount of helium produced to that of the emanation 

 was found to be 3* 18, and as the amount of the emanation found by 

 them was about 1 c.mm. per gramme of radium per day, the result- 

 ing helium, according to this experiment, ought to reach about 3 c.mm., 



* Journ. Chem. Soc, 1907, 1274. 



