[ 320 ] 



XXXVTII. Radium Constants on the International Standard. 

 By Sir Ernest Rutherford, i^ 7 J?. £., Professor of Physics > 

 University of Manchester *. 



DURING the past year, the National Physical Laboratory 

 has obtained a radium preparation certified by the 

 7 ray method in terms of the International Radium Standard 

 preserved in the Bureau des poids et mesures at Sevres. It 

 has consequently been possible to compare the standards in 

 use for many years in the Laboratories in Montreal and 

 Manchester with the International Standard. 



It may be of interest to mention briefly the history of the 

 preparation which for ten years has served as a laboratory 

 standard and in terms of which a number of important 

 radioactive magnitudes have been measured. 



In connexion with the radioactive work in Montreal, it 

 became important in 1903 to adopt a radium standard in 

 which to express the results of various measurements. For 

 this purpose, Professor A. S. Eve weighed out for me 

 3'69 milligrams of a preparation of radium bromide bought 

 from Dr. Griesel, and enclosed it in a sealed tube. This 

 preparation has served as the primary laboratory standard, 

 and was assumed to contain 3*69 milligrams of pure radium 

 bromide or 2*16 milligrams of radium element. At the same 

 time about one milligram of the same material, calibrated in 

 terms of the larger quantity by the 7-ray method, was 

 dissolved and a number of standard radium solutions were 

 prepared. Part of this standard solution was sent to Pro- 

 fessor Boltwood in New Haven in order to make a direct 

 determination by the emanation method of the quantity of 

 radium in a mineral per gram of uranium. The preliminary 

 measurements of Professor Boltwood gave a result much 

 higher than that measured by Professor Eve by direct com- 

 parison of the 7-ray effect of a uranium mineral with the 

 primary standard. It thus appeared that some error had 

 crept in the preparation of the standard solution. An in- 

 vestigation by Eve showed that the radium in the standard 

 solution had partly deposited out on the walls of the glass 

 vessels, and that the solutions were consequently unreliable. 



Another standard solution was then prepared in which the 

 precaution was taken of adding a considerable quantity of 

 hydrochloric acid to keep the radium in solution. These 

 standard solutions are believed to have kept their strength 

 unaltered during the past ten years. With the aid of these 

 standard solutions, the quantity of radium per gram of 

 * Communicated by the Author. 



