S4 ROYAL SOCIETY OF CANADA 



servations made with the emanation from actinium. In these experi- 

 ments, positively and negatively charged electrodes were again exposed 

 in a vessel filled with air and containing a quantity of actinium. In this 

 case as the pressure of the air was lowered the amount of the active de- 

 posit obtained on the negative electrode gradually increased, passed 

 through a maximum value at a certain critical pressure, and ultimately 

 fell away again at the lowest pressure investigated. 



On the other hand in these experiments Euss found that the active 

 deposit obtained on the positive electrode steadily decreased as the pres- 

 sure of the air was lowered. 



Euss also describes a series of experiments in which exposures were 

 made in air when the distance between the actinium and the electrodes 

 was gradually increased. The results which he gives show that, with the 

 air at 760 mm., the amount of the deposit obtained on the cathode 

 steadily decreased as the salt was placed at distances varying from 2 to 

 50 mm. from the electrodes. Under similar circumstances the amount 

 obtained on the anode at first increased as the salt was removed, and 

 finally after passing through a maximum value, fell away again at the 

 longer distances. With the air at 2 mms. pressure, however, the amount 

 'obtained on the cathode steadily increased as the distance of the salt 

 from the electrode was varied from 2 to 42 mms., but the active deposit 

 obtained on the anode with the same variation of distances, gradually 

 decreased. 



In discussing his results Euss points out that Debierne had found 

 that the amount of emanation obtained at atmospheric pressure from a 

 uniform layer of actinium fell to half value in going .55 cms. from the 

 layer and that consequently one would expect to find a decrease in the 

 activity of the electrodes as the salt was removed, and possibly, too, a 

 continuance in the ratio of the activities of the deposits obtained on the 

 two exposed terminals. The results given by him, however, show that 

 this was far from being the case. 



In the various experiments referred to above on the active deposits 

 from radium, thorium, and actinium, the different investigators — with 

 the exception of Debierne — do not appear to have taken any precaution 

 to study the behaviour of the active deposits with uniform electric fields, 

 and, as it was thought that some points which are more or less obscure 

 in connection witli these active deposits might be cleared up if tliey were 

 studied in this manner, it was decided to apply this method to the in- 

 vestigation of the active deposits from actinium, which on account of the 

 short life of its emanation is peculiarly suitable for the study of these 

 active deposit products. 



