528 Mr. W. Makower on the Method of Transmission 



a stopper, through which passed a long capillary tube C 

 reaching to the surface of the solution but not dipping 

 into it. 



The air inside It was thus always kept at atmospheric 

 pressure, and by making C sufficiently long the rate of escape 

 of emanation from the bottle by diffusion was rendered small. 

 After standing for some weeks, the concentration of the 

 emanation in the air above the radium solution was found to 

 have become sensibly constant. 



To transfer a definite volume of gas from R into V, the 

 closed limb a of the three-way capillary stopcock / was con- 

 nected by the capillary b with the vessel Y, to which it was 

 attached by rubber r. By means of a pump the whole was 

 exhausted to a low pressure, when the pump was discon- 

 nected by closing the tap T. The stopcock t was then turned 

 so as to connect a with R, allowed to stand for a short time 

 and then again turned into its original position. In this way 

 the volume a (about '2 c.c.) of gas w T as transferred from B 

 into Y, and by repeating the operation any required volume 

 of emanation could be introduced into Y. 



As the volume of a was always small compared with that 

 of Y. practically all the emanation in a was discharged into Y 

 at low pressures ; at higher pressures it was easy to apply a 

 small correction for the quantity of emanation left in a. 



The pressure in Y was registered on a mercury manometer 

 at the higher pressures, and on a McLeod gauge at the lower 

 pressures. 



The rod AB was exposed for 30 minutes to the emanation, 

 and then transferred to another metal cylinder in which its 

 activity^ was tested in the usual manner by means of a quad- 

 rant electrometer. As under these conditions the activity of 

 the rod remains constant for about 10 minutes*, it was possible 

 to take several observations of the activity, the means of which 

 are recorded in Tables I., II. ; and III. 



3. Observations and Residts. 



Experiments were performed with three vessels Y of 

 diameter 1*1 cm. (vessel I.), 2*6 cm. (vessel II.), and 8*3 cm. 

 (vessel III.) respectively. The pressure of the air with which 

 the emanation was mixed was varied and the activity acquired 

 by the rod in 30 minutes recorded. 



With vessel I. it was found difficult to prevent the rod CD 

 from touching the sides of the cylinder. The arrangement 

 described above was therefore slightly modified by 



* Miss Brooks, Phil. Mag. [6] vol. viii. p. 380 (1904). 



