730 Professor Sir James Deivar [June 11. 



Rate of Formation of Helium from Radium. 



I determined the rate of production of helium from radium in 

 an apparatus consisting of a McLeod gauge, in the construction of 

 which no indiarubber joints were used, the mercury reservoir being 

 connected to an exhaust pump, while the elevation and lowering of 

 the mercury was carried out by admitting and exhausting air in the 

 reservoir. The air coming in contact with the mercury, was purified 

 by passage over stick-potash and phosphoric anhydride. Sealed on 

 to the gauge was a long U tube containing \ grm. of cocoanut 

 charcoal placed in a small enlargement at the bend, the Avhole being 

 arranged for liquid air or other cooling for any desired length 

 of time. The object of this cooled charcoal is to take up and 

 condense all adventitious gases, other than hydrogen or helium, 

 which might arise from minute leakage, or otherwise be generated 

 in the apparatus. The radium chloride was contained in a small 

 bottle standing in a cylindrical glass bulb, connected by a T joint 

 to the U tube. To the other arm of the T was sealed a bulb 

 containing about 15 grm. of cocoanut charcoal for producing a high 

 exhaustion in the apparatus when cooled to - 190° C. Fig. 5 shows 

 the arrangement of the apparatus, except that the special joint B there 

 shown was employed subsequently, as described below. The whole 

 apparatus was well exhausted by mechanical means, all the glass 

 tubes being heated as well as the charcoal receptacles and the radium 

 chloride. On immersing the receptacle containing the 15 grm. 

 charcoal in liquid air for some hours, while the \ grm. charcoal and 

 the radium chloride were kept hot, an exhaust of 0*00015 mm. was 

 obtained. This charcoal receptacle was now sealed off, and the small 

 \ grm. charcoal tube cooled in liquid air. In two hours an exhaust 

 of • 000054 mm. was reached. 



The volume of the gauge and apparatus being approximately 

 200 c.c, the pressure in the apparatus, gives by a simple calcula- 

 tion the actual volume of gas produced measured at atmospheric 

 pressure and the temperature of the laboratory, and thus the rate 

 of production of helium is obtained. This, referred to the weight 

 of radium present, gives the increment in terms of cubic milli- 

 metres of gas per gramme of radium per day. During the first three 

 days the growth of pressure was very small, corresponding to aljout 

 0"3 c.mm. per grm. of radium per day. The cooling of the small 

 charcoal was, however, interrupted owing to the holidays. The 

 emanation consequently was not now completely condensed, but 

 diffused into the McLeod gauge, where it had the opportunity of 

 coming in contact with large surfaces of glass which no doubt held 

 traces of organic matter and water. The result would be that 

 hydrogen would be produced, and errors in the determination would 

 accrue. This was practically confirmed in that the growth of pressure 

 observed was very irregular, and a further experiment was carried 



