732 Radium Emanation in Atmosphere near Earth's Surface. 



use three tubes and to add trie results obtained, as it tends to 

 minimise the effect of small errors. 



Great care was taken to make absolutely certain that the 

 emanation was not derived from radium impurities in the 

 apparatus employed. A very slow current of air through 

 the tubes containing charcoal gave nearly the same result as 

 a u rest " experiment. Charcoal does not absorb well if 

 choked with water- vapour. It seemed sufficient to bubble 

 the air through two flasks of strong sulphuric acid. This 

 acid was always renewed after a calibration experiment, in 

 order to remove any radium which might be carried into the 

 acid from the radioactive solution. 1 found that water and 

 sulphuric acid absorbed but little of the emanation passing 

 through them during these experiments. In any case, the 

 method is comparative, and a slight absorption cannot, 

 therefore, vitiate my results. 



Since Strutt found that one gram of rock, on the average, 

 contained 1*4 x 10 _12 gram of radium, and we have seen that 

 1 cubic metre of the air contains the emanation from about 

 81xl0 -12 gram, we may conclude that 60 grams of rock 

 would provide the radium emanation in 1 cb.m. of the atmo- 

 sphere, if all the emanation escaped from the rocks. But 

 Boltwood has shown that only 5 to 10 per cent, of the 

 emanation escapes from a mineral ; so that by far the greater 

 part of the emanation in rocks, even near the surface of the 

 earth, must undergo transformation without passing into 

 the air. 



Hence, if there enters the air 5 per cent, of the total 

 emanation supplied by the rocks and soils extending to a 

 depth of one or two metres, the supply would be sufficient to 

 account for the emanation in the atmosphere extending to a 

 height of 5 kilometres. 



But radium emanation certainly reaches the atmosphere 

 from considerable depths. Dr. Ruttan has kindly collected 

 for me the natural gas and the mineral water from Caledonia 

 Springs. The water, temperature 40° F., contains only 

 5*6 X 10~ 12 gram of radium per litre ; but 1 cb.m. of the 

 gas contains the emanation from 114,000 X 10~ 12 gram of 

 radium, or about a thousand times as much as a cubic metre 

 of the atmosphere as measured at Montreal. This large 

 output of radium emanation was detected owing to the fact 

 that the gases bubbled through water. In other cases it 

 might escape to no less extent without detection, no water 

 being present. 



It may be observed that in the present state of our 

 knowledge it 3 amount of radium in the earth near the 



