7 hin Films of Elements exposed to Rontgen Hays. 125 



from Ba. When the silver secondary radiator was used, the 

 front of the ionization chamber, being aluminium *75 mm. 

 in thickness, was sufficient to absorb the L radiation from 

 silver. 



The Screens. — These were prepared in the following 

 manner. A brass disk, 12*7 cm. in diameter and - 17 cm, 

 thick, had a brass rim soldered centrally upon it. The rim 

 was 10*2 cm. in diameter and 0*4 cm. deep. In this manner a 

 flat cell was produced 10*2 cm. in diameter and 0*4 cm. deep. 

 Eleven such cells were prepared. These cells were filled 

 with paraffin-wax, the surface being scraped down flat and 

 level with the upper edge of the rim and polished with 

 natural graphite. To obtain films of Au, Sn, and Ag electro- 

 deposition from the double cyanide was employed. A brass 

 cylinder, open at both ends, about 10 cm. in diameter and 

 about 7 cm. high, was stood upon the graphited wax plate w 

 (fig. 1). The inside of this cylinder was waxed so as to 



Fig. J 



prevent contamination, e is an ebonite block. By an 

 arrangement of an indiarubber ring sealed round the edge of 

 the cylinder, and an annular tinfoil electrode t stuck on the 

 indiarubber ring, good electric contact could be made with 



the graphite surface. The electroplating solution was then 

 poured into the cell, a suitable anode a dipped in. and 

 deposition started on S and judged by the eye. In the ease 

 of these three substances, the films were uniform and so 



