858 



SCIENCE 



[N. S. Vol. XLII. No. 1094 



This work was undertaken in the univer- 

 sity year 1913-14 in my laboratory by Miss 

 Ellen Gleditsch, who came to this country 

 from Norway for a year of study on a fel- 

 lowship of the American Scandinavian 

 Foundation. The work has been carried 

 out in a very satisfactory manner and, 

 after encountering a number of difficulties, 

 she has quite recently completed her ex- 

 periments at the University of Kristiania. 

 A paper by her on the subject will appear 

 in the January number of the American 

 Journal of Science. 



Miss Gleditsch carried out four separate 

 operations, which may be briefly described 

 as follows : 



The first was with a specimen of very 

 pure North Carolina uraninite weighing 

 110 grams and containing 2.46 X 10"° gram 

 of radium. The growth of radium from the 

 ionium separated from this material gave 

 a value for the constant of change of 

 3.7X10"* (per year), which corresponds 

 to a half-value period of 1,836 years. 



The second was with a specimen of Nor- 

 wegian uraninite known as Cleveite, weigh- 

 ing 180 grams and containing 3.2 X 10"" 

 gram of radium. The ionium separated 

 from this material grew radium at a rate 

 corresponding to a value for the constant 

 of 3.9 X 10"* and a half-value period of 

 1,780 years. 



The third was with a specimen of Nor- 

 wegian uraninite of the variety known as 

 Broggerite, weighing 200 grams and con- 

 taining 4.1 X 10"* gram of radium. In 

 this experiment the radium grew at a rate 

 corresponding to 4.2 X 10"* for the value 

 of the constant and indicated a half-value 

 period of 1,640 years. 



In the fourth experiment a specimen of 

 very pure Broggerite was used, weighing 

 100 grams and containing 2.1 X 10"^ gram 

 of radium. The value obtained for the 

 constant of change of radium was 4.1 X 10~^ 



and the half-value period corresponds to 

 approximately 1,670 years. 



In this series of experiments the methods 

 for effecting a complete separation of the 

 ionium were progressively developed and 

 improved. In the last two, the ones in 

 which broggerite was used, there were defi- 

 nite indications that a complete separation 

 had been accomplished. Moreover, Miss 

 Gleditsch also measured the amount of 

 radium in one of my original ionium solu- 

 tions in which the radium had been grow- 

 ing for a period of nearly seven years and 

 found that the rate of growth had been 

 constant throughout the entire interval. 

 This fact disposes of the possible objection 

 that the life of ionium is too short to give 

 an accurate value for the constant of 

 radium as determined by this method. 



It is therefore apparent that the differ- 

 ent methods which have been used for esti- 

 mating the life of radium give results 

 which are in excellent agreement with one 

 another. This agreement increases the as- 

 surance with which the estimated values 

 of certain important physical constants 

 involved in the calculation can be accepted 

 as approximating closely to the true values. 

 As a matter of interest these constants will 

 be mentioned. 



Number of a-particles emitted per sec- 

 ond by one gram of radium (element) 

 = 3.57 X 10-^". 



The charge carried by a hydrogen ion in 

 electrolysis = 4.65Xl0"'"' E.S. units. 



The number of atoms in one gram of hy- 

 drogen = 6.2 X W. 



The mass of the hydrogen atom = 1.61 

 X 10"^* gram. 



The number of molecules in one cubic 

 centimeter of any gas at standard pressure 

 and temperature = 2.72 X 10". 



The volume of the radium emanation in 

 equilibrium with one gram of radium 



