[ 660 ] 



LXVIII. A Comparison of Radium Standard Solutions. 

 By J. Moran, B.Sc, McGill University *. 



Section 1. History. — (a) Solid Standards. 

 ri^HB fundamental Radium Standard of the present time is 

 JL the International Radium Standard at Sevres, France. 

 It was prepared by Mine. Curie in 1912, on the recom- 

 mendation of the Congress of Radiology and Electricity 

 which met at Brussels in 1910 f . It consists of 21*99 milli- 

 grams of pure radium chloride, sealed up in a thin glass 

 tube. This standard, before being accepted, was compared 

 with three other purified amounts of radium chloride, pre- 

 pared by Honigschmidt for atomic weight determinations. 

 These all agreed with Mme Curie's standard to within one 

 part in three hundred. One of Honigschmidt' s preparations 

 has been preserved at the Radium Institute of Vienna, as a 

 secondary standard, and termed the Vienna Standard. 



Before this, however, in 1903, the first radium standard 

 was prepared at McGill University, Montreal, and termed 

 the Rutherford-Boltwood Standard. A quantity of pure 

 radium bromide was bought from Dr. Giesel of Germany, 

 and generously presented to McGill University by Sir 

 William Macdonald. Of this amount, 3*69 milligrams were 

 weighed out and sealed up in a tube by Professor Eve and 

 Dr. Levin, and thereafter constituted a primary laboratory 

 standard. It is now at Manchester University, England. 



Various secondary national standards exist, examples of 

 which are the English standard at the National Physical 

 Laboratory and the Washington standard in U.S.A. These 

 have all been accurately compared with the International 

 and Vienna standards. 



After the preparation of the International standard, the 

 Rutherford-Boltwood standard was carefully compared with 

 it, and also with the Vienna standard. It was compared 

 indirectly with these by means of the secondary standard 

 at the National Physical Laboratory. These investigations 

 showed that the Rutherford-Boltwood standard consisted of 

 3*51 instead of 3'69 milligrams of radium bromide. It is 

 therefore 4*9 percent, low on the International. It is known 

 that radium bromide on exposure to air gives up bromine, 

 and changes over to the carbonate, while water of crystal- 

 lization is also formed. This is suggested by Sir Ernest 

 Rutherford as an explanation of the increase of weight. 



(b) Solution Standards. 



For laboratory purposes a solution standard is prepared. 



* Communicated by Prof. A. S. Eve, D.Sc. 



f '•'Radioactive Substances and their Radiations," 1913 ed. Bv Sir 

 Ernest Rutherford. See also Phil. Mag. Sept. 1914 (Sir E. Rutherford). 



