Radioactivity of Radium and Thorium. 457 



the a radiation, and the view was pnt forward that this stage 

 probably represents a double change in the case of .thorium, 

 and a treble change in the case of radium. In the latter 

 there is (for a short exposure to the emanation) a very rapid 

 decrease for the first 10 minutes to about 20 per cent, of the 

 original value, then a period of very slow change, and then 

 a more regular decay in which the remaining activity falls to 

 half value in about 30 minutes. 



Now the decay curve of the j3 radiation of the radium- 

 excited activity shows a fairly regular decrease to half value 

 in 30 minutes. Hence there is strong evidence that the {3 

 rays are not given out in the first change of the excited 

 activity, but only in the second or third change. 



Eadium therefore fully supports the view already advanced 

 that the a rays are in all cases the first to be produced, the /3 

 rays only resulting in the last stages of the process that can 

 be experimentally traced. 



§ 6. The Chemical Nature of the Radium Emanation. 



The experiments already described on the chemical nature 

 of the thorium emanation were repeated for that of radium. 

 As in the former case all the reagents tried were without effect. 

 The emanation passed unchanged through phosphorus pent- 

 oxide, sulphuric, nitric, and hydrochloric acids, and over red- 

 hot lead chromate and metallic magnesium. Water does 

 not dissolve the emanation appreciably, and the activity of 

 the water is solely due to the presence of the excited activity. 

 The emanation in both dry and moist atmospheres is un- 

 affected by passage through a platinum tube electrically heated 

 to the point of incipient fusion. An interesting effect, how- 

 ever, was observed as the temperature approached a white 

 heat in this experiment, 



The ionization current due to the emanation decreased with 

 rise of temperature, but returned to its original value when 

 an increased voltage was applied sufficient to give a saturation 

 current through the gas. This effect is due to fine platinum 

 dust given off from the white-hot platinum, and is quire 

 analogous to that of tobacco-smoke observed by Owens (Phil. 

 Mag. 1899, xlviii. p. 377) in this laboratory. 



The condensation of the radioactive emanations of thorium 

 and radium at the temperature of liquid air (Proc. Ohem. 

 Soc. 1902, p. 219) will be dealt with in detail in a separate 

 communication. 



McGill University, Montreal, 

 Feb. 20, 1903. 



