634 Mr. L. B. Smyth on the Supply of Radium 



1 cm. in diameter from which a vertical tube rises through 

 the opening in the top or the tin vessel. From this tube a 

 line of lead and rubber pipes run to a suction-pump in the 

 laboratory, a distance o£ about 45 feet. Immediately before 

 each experiment the tin vessel was placed in position, usually 

 not on the same spot it occupied during the next preceding 

 experiment. When suction is applied, air enters by the 

 aperture in the tin vessel, flows over the margin of the tin 

 disk, and, after sweeping over the surface of the ground, and 

 presumably carrying away any emanation given off therefrom, 

 it enters the system of pipes. On arriving in the laboratory 

 it is made to traverse a quartz tube of 1*5 cm. bore, containing 

 coarsely powdered coconut charcoal which absorbs the 

 emanation. The rate of suction was usually about 20 litres 

 per hour; but variations in this were not found to have any 

 noticeable effect, as probably a much slower current would be 

 sufficient to carry away all the emanation exhaled. When the 

 suction has continued for an hour, the quartz tube is attached 

 to a rubber bag, and heated in a gas-furnace for about half an 

 hour. The contents of the bag and tube are then transferred 

 to an electroscope which is observed as before. 



The results are reduced to amounts of emanation escaping 

 from 1 sq. m. per hour, and are, as before, expressed in 

 curies x 10 ~ 12 . 



The error due to the amount of emanation in the atmosphere 

 at the time of the experiment has been neglected. 



Results. 



The results of the two series of experiments have been 

 plotted together (PL XIV.) , the exhalation results having 

 been divided by 100 in order to have them close to the others. 

 The dates are marked on the abscissa line. The ordinates are 

 amounts of radium emanation in curies X 10 " l2 . The full 

 line represents exhalation, the broken line ground-gas. Along 

 the top of the diagram the weather is indicated. In the 

 weather indications S. stands for stormy, F. for frost. 



As might be expected, the results are very irregular. The 

 conditions influencing the escape of emanation from the 

 soil spaces to the atmosphere are very complex, and the 

 various factors interfere with one another. The exhalation, 

 being less capable of exact determination under natural con- 

 ditions, besides being probably more liable to rapid variations, 

 will in general yield less reliable results than the ground-gas. 

 The figures arrived at, too, only represent the state of things 

 during one hour in forty-eight. 



