Production of Helium by Radium. 589 



Since it is important that the rate of production of helium 

 by radium should be known as accurately as possible, an 

 independent determination of this magnitude has been 

 carried out by the writers. Two separate determinations of 

 the rate of production of helium have been made, using for 

 the purpose a considerable portion of the specimen of radium 

 salt kindly loaned to one of the writers by the Vienna 

 Academy of Sciences. 



Preparation of Material. 



It was quite essential that the radium salt used in these 

 experiments should be relatively free from radioactive sub- 

 stances other than radium. The salt consisted of a quantity 

 of barium-radium chloride, containing about 7 per cent, of 

 the latter element, and before it came into our hands had 

 been originally subjected to a partial fractional recrystalli- 

 zation. Lt was therefore highly improbable that radioactive 

 substances other than radium and the disintegration products 

 of radium were present. The salt had been preserved in a 

 slightly acid, aqueous solution for a period of over a year 

 previous to the time when these experiments were begun, 

 and had existed in the form of a crystalline salt for a some- 

 what indefinite period before this. In order to remove the 

 radio-lead and polonium which had accumulated during this 

 interval the solution was treated as follows : — About fifty 

 milligrams of antimony trichloride, ten milligrams of lead 

 nitrate, and five milligrams of bismuth nitrate were dissolved 

 in a small quantity of dilute hydrochloric acid, and this 

 solution was added to the solution of the radium salt. The 

 mixture was diluted with water to a volume of about 100 c.c. 

 and an excess of hydrogen sulphide was run in. Because of 

 the addition of the antimony salt, the precipitate of sulphides 

 coagulated and could be readily removed by filtration through 

 paper, after which it was well washed with distilled water. 

 The precipitate on the paper was decomposed by warming 

 with dilute hydrochloric acid to which a few small crystals 

 of potassium chlorate had been added, and. after diluting 

 with water, the treatment with hydrogen sulphide was 

 repeated. The second precipitate of sulphides was filtered 

 off and the filtrate was added to the filtrate from the first 

 operation. The object in adding the lead and bismuth salts 

 to the original solution was to insure the complete separation 

 of the radio-lead and polonium *. 



The combined filtrates from the sulphides were evaporated 



* Boltwood, American Journal of Science, vol. xxv. p. 228 (1908). 



