K X-rays of Silver in Gases and Gaseous Mixtures. 383 



and initial intensity 96 per cent., and /* = 2'34 and initial 

 intensity 4 per cent.* 



(2) Measuring Apparatus (see fig. 2). 



To determine the absorption produced by various gases in 

 the absorption chamber, a ratio method was used in which 

 the intensity of the main beam after passing through the 

 chamber was compared with the intensity of a beam of 

 similar rays passing always unaltered into a standard ioniza- 

 tion vessel. 



Fig. 2 (to scale). 



I — main Ionization chamber ; S — standard ; A — Absorption chamber ; 

 F — silver filter ; R. — silver radiator ; B — X-ray bulb. 



The absorption chamber was a stout aluminium cylinder, 

 50'8 cm. long, 12 cm. in diam., with each end closed with 

 two circular aluminium plates, 4 mm. thick, holding between 

 them a thin aluminium sheet f (*1 mm.). These two plates 

 for each end were drilled with the maximum number of 

 holes (8 mm. diam.) so that the X-rays could pass through 

 the thin sheet in the " windows " thus formed. Three long- 

 rods ran the length of the cylinder and bolted the ends 

 against the cylinder, and all the joins were cemented w T ith a 

 plastic wax made with resin, beeswax, and a little turpentine. 



* The analysis was made from the absorption curve (log - I/thickness 

 of Al), generally graphically, but also by the analytical method given by 

 Sir J. J. Thomson, Phil. Mag. Dec. 1915. 



t Celluloid and vaselined parchment were both attacked by S0 2 . 



