432 Mr. S. Ratner on the Distribution of the Active 



easily opened by taking out one of the glass windows. In 

 the aperture aa of the plate A fine copper wires are stretched 

 6 mm. apart in order to support a small disk R 7 and so as 

 not to interfere with a current of air. In the apertures a a 

 and b b are fixed two tubes ti and t 2 of square section (for 

 ease of construction), made from flat pieces of tin sheeting 

 in the form shown in the figure. By means of pieces of 

 rubber-sheet S they are insulated from two other tubes t z 

 and t± of the same shape, which are fixed in two square 

 apertures c c and d d, cut in the two opposite faces of a tin 

 cube K. The face CD of this cube may be easily removed, 

 and is provided in the centre with an ebonite plug N" through 

 which passes a brass rod L carrying a plate P. The whole 

 apparatus forms a closed vessel allowing free circulation of 

 air through the condenser AB, the tubes £, and the cube K. 

 The current of air is produced by a potential difference 

 established between A and B and a source of ionization. The 

 small disk R, after a long exposure in an electric field to a 

 large quantity of emanation, is quickly removed from the 

 emanation vessel and placed in the centre of the plate A. 

 The plate B is charged to a negative potential, while A and 

 the cube K are earthed. A certain part of the recoil atoms 

 of radium B, as shown in the previous section, are carried 

 by the electric wind in the direction indicated by the arrows 

 and are constantly circulating through the apparatus, so that 

 the cube K forms a vessel filled with uncharged radioactive 

 recoil atoms in slow and constant motion. The preliminary 

 experiments consisted in studying the distribution of these 

 atoms in an electric field. 



The dimensions of the apparatus are as follows : — 



The plates A and B 12x12 cm. 



Ape rtures a a and cc ... 6x 6 



Apertures b b and dd 3x 3 



Distance between A and B 3 



The cube K 10x10x10 



Diam. of plate P 5 ,, 



Diam. of disk R 1*5 „ 



In the absence of an electric field the activity diffusing 

 towards the inner surface of the vessel K was found to be 

 very small and uniformly distributed over the walls of the 

 cube and the plate P. Since the recoil atoms of radium B 

 present in the vessel are not charged, their distribution 

 should not be affected by an electric field. The experiments 

 show, however, that if the plate P be charged, positively or 

 negatively, the activity acquired by it is largely increased. 



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