566 Mr. E. P. Adams 



on 



with dry air from the room, the leak in tlie electroscope was 

 at the rate of 0"5 division per minute. But with the air 

 boiled out of water through which radium emanation had 

 passed, the rate increased to 10 divisions per minute, and 

 after about two hours it increased to 18 divisions per minute. 

 It then began to decrease. On allowing the same sample of 

 water to stand for several days, and again testing the air 

 drawn through it as above, it was found that the rate of leak 

 was the same as for air taken directly from the room. This 

 shows conclusively that a small amount of radium emanation 

 is absorbed by water, nnd that the effect observed is not due 

 to radium carried over in spray from the radium solution. 

 The oLiss-wool plug stopped all of that. 



When the same volume of water direct from the tap is 

 tested in the above way, the maximum rate of leak is about 

 2 divisions per minute. But this varies considerably at dif- 

 ferent times. Hence a very small quantity of radium 

 emanation dissolved in water would be sufficient to account 

 for this. 



Equal volumes of water containing the emanation in solu- 

 tion were tested from day to day to see whether the radio- 

 activity decayed at the same rate in solution. It was found 

 that the decay was considerably greater than for emanation 

 kept in a closed vessel. The reason for this is that the decav 

 is due to two causes : first, the decay in radioactivity of the 

 emanation itself ; and second, the escape of emanation from 

 the solution. But a sample of water containing emanation 

 in solution, when kept closed so that none of the emana- 

 tion can escape, is found to decay at the same rate as 

 emanation which is kept in a closed vessel. 



But an important difference Iihs been found between dis- 

 tilled water containing radium emanation in solution and 

 tap-water. After the former has been thoroughly boiled so 

 as to drive out all the emanation, it entirely loses its radio- 

 activity, and on letting it stand for any length of time, and 

 again testing the air drawn through the boiling water, this 

 air is found to have no greater conductivity than air taken 

 direct from the room. But with tap- water it is different. 

 It is impossible to get rid of the radioactivity entirely by 

 boilino- the water so as to drive out all the dissolved eases. 

 A minute trace remains. In fact, tap-water behaves as if it 

 contained, in addition to dissolved emanation, an extremelv 

 minute quantity of a radium salt in solution. All attempts 

 to evaporate a large quantity of water to dryness, and to find 

 any radioactivity in the solid residue, have so far failed. 

 But the evidence for the presence of the radioactive salt is 



