and its Successive Products. 43 



electrodes were placed ; during the measurements one of the 

 electrodes was connected with an electrometer and the other 

 two were earthed. 



Both actinium X and actinium deprived of AcX were 

 placed in solutions of ammonium chloride in two bubbling 

 flasks, and these could be successively connected with the 

 testing cylinder in which the amount of emanation was 

 measured. For the purpose of comparison with a substance 

 of a standard emanating power, the following arrangement 

 was used. 



The current o£ air passed through the bubbling bottle and 

 carried with it the emanation of the product to be investi- 

 gated. It thus passed through the testing cylinder, in which 

 the activity of the emanation was measured. On leaving the 

 cylinder, the current of air entered a glass tube 2 cms. in 

 diameter and about 3 metres long. At the end of this glass 

 tube some fresh solid actinium was placed, and the emanation 

 from this was carried into the second testing cylinder where 

 its activity was measured. 



In this manner the same current which carried the emana- 

 tion from the product under investigation also carried the 

 emanation from the standard actinium. In passing through 

 the long and wide glass tube the emanation which left the 

 first cylinder decayed completely before reaching the second 

 cylinder. By this method of measurement, the emanating 

 power of AcX was directly compared with the standard 

 emanating power of solid actinium. 



The experiments made in this manner showed: 



(1) That the actinium immediately after removal of AcX 



gives practically no emanation. 



(2) That the rate of increase of the emission of emanation 

 of actinium after removal of AcX is the same as the 

 rate of increase of its activity. 



(3) That the emanating power of AcX decreases at the same 



rate as the activity of AcX. 



Since the emanation is only observed when actinium X is 

 present, and is always proportional to the amount of actinium 

 X, it must be a product of actinium X. 



The changes occurrino; in actinium are shown in the 

 following graphical representation*, together with the period 

 required for transformation to half value. For comparison 

 the changes taking place in thorium are also given. 



* See Rutherford, Bakerian Lecture, loc. cit. pp. 180-190 & 204; also 

 Miss Brookes, Phil. Mag. Sept. 1904, pp. 382-384 ; also Bronson, Amer. 

 Journ. of Science, vol. xix. Feb. 1905, p. 187. 



