A Comparison of Radium Standard Solutions. 661 



This is obtained by comparing a small quantity of tbe radium 

 salt with a solid standard by the 7-ray method. It is then dis- 

 solved in distilled water with a little HC1, to keep it in solution. 



Such a solution, but with no acid added, was made up 

 by Eve at about the same time as the preparation of the 

 Rutherford-Boltwood solid standard, using about one quarter 

 of a milligram of radium bromide. Determinations by 

 Boltwood a few years later at New Haven with some of this 

 solution led to results which conflicted with those obtained 

 by Eve in similar work, where the solid standard was used. 

 It was shown by the latter that the original solution had 

 weakened by the deposit of radium on the walls of the flask, 

 as no hydrochloric acid had been used in the preparation. 

 Two new solutions were then prepared by Boltwood from a 

 known amount of radium bromide, determined by Eve by 

 the 7-ray method. These solutions were of strength in the 

 ratio of 100:1, one containing 1*57 x 10~", and the other 

 1*57 xlO -9 gram of radium per c.c. This time a little HC1 

 was added as a precaution, to keep the radium in solution. 



Since the Rutherford-Boltwood solid standard is known 

 to be 4*9 per cent, low on the International, and the Ruther- 

 ford-Boltwood solution standards were compared with the 

 former, considerable importance attaches to finding whether 

 its accepted value may not also be in error, and to what 

 extent. The more so, since determinations by Boltwood on 

 the relative amounts of uranium and radium in rocks, and 

 results obtained by Eve and others for the amount of eman- 

 ation in air, and also of radium in rocks and water, are based 

 upon these solution standards at their present accepted value. 

 The investigation was carried out by comparing the weak 

 solution of the Rutherford-Boltwood standard with a solution 

 of the Washington standard. A litre of the latter was 

 obtained by Eve in Sept. 1914, from Satterly of Toronto 

 University, containing 9*15 xlO -11 gram of the radium 

 element per c.c. It was certified as follows : — 



" 100 c.c. of acid solution of the Washington Standard of 

 strength 12*2 x 10~ 9 gm. of radium per c.c. 10 c.c. of this 

 were diluted to one litre. 250 c.c. of this were removed, 

 and distilled water added to the remaining 750 c.c. to make 

 up one litre, the strength of which was now three-fourths 

 the strength of the previous litre, or 9*15 xlO -11 gm. of* 

 radium per c.c. Radium contents declared right with the 

 International Standard to an accuracy of at least one-third 

 per cent. Density of solvent HC1 1 '08. Combined errors 

 scarcely one per cent." 



Experiments were carried out by the writer with the strong 

 and the weak solutions of the Rutherford-Boltwood standard. 

 These served to compare the Rutherford-Boltwood standard 



