540 Mr Satterly, Radium- content of Cambridge Waters. 



Note on the Radium-content of the Waters of the Cam, Cam- 

 bridge Tap Water and some varieties of Charcoal. By John 

 Satterly, B.A., B.Sc. (Lond.), St John's College. (Communicated 

 by Professor Sir J. J. Thomson.) 



[Eeceived 24 June 1910.] 



In view of the fact that the author has found more radium 

 emanation in the air at Cambridge* than Eve found in the air at 

 Montreal f it was thought that it would be of interest to examine 

 quantitatively the water of Cambridge for radium. 



Some experiments have already been made on the radio- 

 activity of Cambridge tap water. J. J. Thomson^ showed that 

 air bubbled through this water became radioactive due to the 

 removal from the water of some dissolved gas. Adams§ tested 

 this gas and identified it with radium emanation. He also 

 established that the water contained dissolved radium as well, 

 for after boiling the water and clearing out the dissolved emana- 

 tion a little emanation accumulated when the water was allowed 

 to stand for some days ; he states that the recovery was about 

 one-tenth of its previous value. Adams evaporated quantities of 

 water to dryness but failed to find any activity in the residue, 

 Strutt||, who employed Cambridge tap water in the aspirators 

 which he was using in his work on the estimation of radium in 

 rocks, states that no measurable quantity of emanation was 

 generated in the water which had been previously boiled, although 

 a close examination of his figures shows that two litres of water 

 generated in a fortnight enough emanation to send up his air- 

 leak about 4°/^. None of the above experimenters however had 

 at the time the means of expressing the amount of emanation in 

 terms of the mass of radium which would generate it. 



Recently EvelT has examined the water of the St Lawrence 

 which is delivered as the town supply of Montreal without any 

 filtration or other treatment, and found its radium-content to be 

 •25 X 10~^^ gm. of radium per litre of water, and Joly has found for 

 the Nile 4-2 x 10~^l For sea-water from the North Atlantic, 

 EveH has found on the average '9 x 10~^^ gm. of radium per litre, 



* Phil. Mag. Oct. 1908 and July 1910. 

 t ibid. Oct. 1908. 

 J ibid. Sept. 1902. 

 § ibid. Nov. 1903. 



II Roy. Soc. Proc. A, Vol. lxxvii. 1906. 

 H Phil. Mag. July 1909. 



