Mr latterly, Radium-content of Cambridge Waters. 541 



and Joly 16 x 10~^^*, and more recently 12 x 10~^^f as an average 

 of sea-water from all over the world. 



The method of testing in my experiments was to take the 

 water straight from the Cam or the tap and boil it in a flask 

 connected to a condenser and aspirator. When the water was 

 boiling air was rapidly drawn through it by the aspirator; the 

 emanation was thus withdrawn and collected in the aspirator. 

 The steam condensed in the condenser and ran back into the 

 flask. The emanation-charged air in the aspirator was then passed 

 into a previously exhausted testing vessel and the leak taken. 

 This leak less the normal air leak is a measure of the emana- 

 tion. 



The waters of Cambridge contain much chalk in solution, so 

 that unless acidified a deposit occurs on boiling. As this might 

 affect the quantity of emanation given off two samples of each 

 water were tried, one untouched and the other acidified with a 

 little hydrochloric acid (the acid itself was tested and though not 

 free from radium yet would, as only a small quantity was used, 

 contribute practically no emanation, see Table II). 



In the first set of experiments a litre of water was taken each 

 time, and when acidified two c.c. of acid was used. After each 

 boiling the flask was corked up and allowed to stand for any 

 emanation to accumulate when the water was again reboiied and 

 the emanation drawn off and tested. It was found that practically 

 no emanation was accumulated on resting, so that practically all 

 the emanation initially present in the water is just dissolved 

 emanation. 



Table I gives the first set of results ; the amount of emanation 

 being expressed on an arbitrary scale (the numbers are the leaks 

 per minute in the testing vessel as read on the scale provided to 

 the electrometer. The air leak which was about I'O has already 

 been subtracted). 



Table I. 

 Cambridge tap water (one litre). Cam water (one litre). 



* Phil. Mag. May 1908. 



t ibid. Sept. 1909. 



