198 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 54 



EADIUM. 



The early, preliminary attempts to determine the atomic weight of 

 radium may be ignored, for they were made with confessedly impure 

 material. In 1902 Madame Curie ' published the first determinations of 

 any value, basing them upon the following analyses of radium chloride. 

 The ratio 2AgCl : EaCl, is given in the third column : 



RaCL. AgCl. Ratio. 



.09192 .08890 103.397 



.02936 .08627 103.582 



.08839 .08589 102.911 



Mean, 103.297, ± .1349 



Hence Ea= 225.31. 



In the foregoing determinations the radium chloride still contained 

 appreciable amounts of barium chloride. In a later series of determina- 

 tions Madame Curie ' used purer material, and in much larger quan- 

 tities. The results obtained were as follows: 



Mean, 103.695, ± .0236 



Hence Ea= 226.35. 



Still more recent are the determinations by Thorpe,* on small quan- 

 tities of material: 



Mean, 103.774, ± .1399 



Hence Ea = 326.58. 



Thorpe regards his figures, however, as merely corroborative of Madame 

 Curie's. A combination of the two series gives 103.700 for the general 

 mean, and Ea= 226.37. 



1 Ann. Chim. Pliys. (7), 30, 140. 1903. Pioliminary data in Compt. Rend., 135, 80. 1902. 



= Compt. Rend., 145, 422. 1907. 



' Corrected for the weight of filter ash. 



*Proc. Roy. Soc, 80, A, 298. 1908. 



