[eve] on the amount OF RADIUM PRESENT IN SEA-WATER 



31 



A glass flask, silvered inside, was fitted as an electroscope and 

 the method followed was that described in a previous paper.* The 

 natural leak was small and constant. 



After the sea-water and acid had been sealed about a month 

 in the flasks they were boiled for some minutes and all the gases 

 driven off, including the emanation, were collected over wafer and 

 introduced through a drying tube into the electroscope. As the 

 method is a comparative one there appears to be little objection to 

 collecting over water. Nevertheless it might be objected that the 

 radium emanation is absorbed by bubbling through water to a vari- 

 able and unknown extent. Therefore re-determinations were made 

 by collecting over mercury. There was no certain observable dif- 

 ference between the two methods. It is often simpler and it seems 

 perfectly safe to collect over water. 



To calibrate the electroscope I prepared solutions of radium 

 bromide, using those standard solutions whose history is given in 

 the American Journal of Science, Vol. 22, July 1906. These same 

 standard solutions were those also used by Rutherford and| Bolt- 

 wood in their determinations of the ratio of uranium to radium in 

 pitchblende. As Joly used this ratio for calibration our standards 

 are practically the same. Moreover Strutt, Joly, Eve and Mcintosh 

 all find values for the radium contents of rocks which are in satis- 

 factory agreement, so that the question of relative standards does 

 not arise. 



One c.c. of the standard solution, containing 1,57 x 10~^ gram 

 of radium, was taken with a new and clean pipette and placed in a 



* In the Gulf of St. Lawrence. 



^ Eve and Mcintosh, Phil. Mag., Aug. 1907. 



