296 Boltwood — Radio-activity of Uranium Minerals. 



the radium deposit from the standard solution was approxi- 

 mately 0*52 of the activity of the uranium with which it would 

 be associated in a mineral. This is about 0*07 X II higher than 

 the value obtained with a freshly prepared radium salt (p. 282). 

 If the amount of polonium to be expected in the old radium 

 salt is calculated from the half-value period (12 years) of radium 

 D as recently determined b} T Meyer and Schweidler* and the 

 half-value period of radium F (polonium) generally accepted 

 (143 days), it is found that about 17 per cent of the equilibrium 

 amount of polonium would be formed in a period of four years. 

 •The relative activity of seventeen per cent of polonium would 

 be 0'48x0 - 17, namely, 0*08 XU, and this number is in good 

 agreement with the value found above. 



Emanating Power of Radium Sulphate.- — It was noted in 

 the course of certain experiments that the emanating. power of 

 radium sulphate in the form of a thin film was not a negligibly 

 small quantity. From a film containing about 10~ 9 gram of 

 pure radium sulphate per square centimeter the loss of radium 

 emanation was nearly 10 per cent of the total. The radium 

 salt had been dried, by heating to a low red heat. 



Relative Amounts of Radium and Uranium in Minerals. 



The value for the amount of radium in equilibrium with one 

 gram of uranium in a mineral given in the paper by Rutherford 

 and Boltwoodf is somewhat in error because of the incorrect 

 assumption as to the proportion of uranium in the mineral 

 used4 Instead of 68 c 2 per cent of uranium the mineral 

 actually contained 75*8 per ceut of uranium. The amount of 

 radium associated with one gram of uranium in a mineral is 

 therefore about 3'4xl0~ 7 gram, instead of 3'8xlO" 7 gram. 



Relative Activity of Radium and Uranium. 



The relative activity of the radium present in a uranium 

 mineral has been shown to be 0*45 times the activity of the 

 uranium with which it is associated. The amount of radium 

 associated with one gram of uranium in the same mineral has 

 been found to be 3 - 4xl0~ 7 gram. One gram of uranium 

 will therefore have the same activity as 7*5 XlO -7 gram of 

 radium, and one gram of radium (free from all products) will 

 have the same activity as 1,300,000 grams of uranium. One 

 gram of radium containing its equilibrium amount of the prod- 

 ucts radium emanation, radium A, radium B, and radium C 

 will have about the same activity as 7'3 X 10 6 grams of 



*Phys. Zeit., viii, 457, 1907. f This Journal, xxii, 1, 1906. 



X The error arose from the difficulty encountered in obtaining a pure 

 uranoso-uranic oxide. Page 282. 



