214 



36 



the emanation, will cause a perceptible alteration in the ionisation curve. On this 

 account this method is always a little unreliable, and I therefore laid particular 

 stress on the second method. 



In order to determine the coefficient of the rate of decay of the emanation, 

 I took two samples of every spring gas to be examined, one sample about 100 ccm., 

 the other about 200 ccm. As soon as possible, (after /i seconds), the 100 ccm. of the 

 gas were examined to ascertain the emanation contained, whilst the 200 ccm. of 

 the gas were examined after about four days (^2 seconds). 



By means of the measurements above described, the emanation contained in 

 1 ccm. of the spring gas under examination, at the moment when the gas was 

 introduced into the testing vessel, was then calculated. Let A^ and A; represent 

 the emanations calculated per 1 ccm. of spring gas, while the indices /i and t^ 

 signify the time in seconds that the testings took place after the collection of 

 the gas, then At is the emanation in 1 ccm. of the spring gas after having been 



^1 seconds in the collecting bottle, and Ai has an ana- 

 logical significance. Therefore At^ is the remainder of 

 the emanation At after t^ — ti seconds. 



In order to calculate the rate of decay («') of the 

 emanation by means of the two experiments, it is 

 necessary to suppose that the emanation decays in 

 accordance with a known law. By supposing that the 

 emanation decays according to an exponential law 



1 eet 



At,^ == ^,_e-«'('-'.)- 



Hence 1 have 



log At — log A, 



Fig. G. „' _ ^AJ^ ^_J?. 



■ 2 — «1 



The values of the rate of decay entered in Table I are calculated in accord- 

 ance with this formula. 



The examination of the radioactive substances in solids, i. e. mud and sedi- 

 ments, was done by measuring their ionising power. The apparatus for measuring 

 the ionisation produced by solids was, in principle, the same as that employed in 

 examining the emanation. The same electroscope was used, but the ionisation 

 vessel had different dimensions. The vessel / in Fig. 6 is 12 cm.] high and 26 cm. 

 in diameter. A circular, horizontal plate of zinc, Z, 16 cm. in diameter, is con- 

 nected by a brass rod 6 cm. in length to the rod, g, in the electroscope. The 

 brass rod is attached to the centre of the plate. The substance to be examined is 

 pulverized finely and spread in a thin layer over the bottom of the vessel, which 

 is easily removed from the upper part. The radium rays emitted by the substance 

 will then ionize the air in the testing vessel and consequently augment the leakage. 



One can form an estimate of the sensitiveness of the apparatus from the fol- 

 lowing measurements. 1 dissolved 0.201 gram of nitrate of uranyl, {U02{N03)2^ &H2O), 



