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XXXIX. The Absorption of the K X-rays of Silver in Gases 

 and Gaseous Mixtures. By P. W. Buebidge, M.Sc. (JY.Z.), 

 B.A. (Cantab.), 1851 Exhibition Scholar, Trinity College, 

 Cambridge *. 



I^HE published results o£ experiments on the ionization 

 of mixtures of gases f show discrepancies from the 

 results expected on the accepted theory that the ionization 

 is due to corpuscles ejected by the Rontgen rays from the 

 atoms of the mixture. It seemed worth while, in view of 

 the failure of other explanations, to test directly the assump- 

 tion that the absorption of the energy necessary to eject these 

 corpuscles was independent of the association of the gases in 

 the mixture — i. e., that this " ionization absorption " is an 

 atomic phenomenon and therefore in a gaseous mixture 

 strictly additive. From the well-known results of the direct 

 test with solids and liquids, this assumption for gases seemed 

 quite probable and received support from the work of 

 H. Moore {, who has calculated absorption coefficients on 

 this basis, but, since the accuracy of Moore's comparison was 

 necessarily very limited, it was judged advisable to make a 

 few direct experiments. During the course of these, some 

 measurements of absorption coefficients were also obtained. 



Experimental Methods. 



(1) X-Rays. 



As a source of strong homogeneous radiation an attempt 

 was made to utilize the direct rays from a palladium anti- 

 cathode, but the nature of the radiation was too dependent 

 on the hardness of the bulb, and the method was therefore 

 abandoned and secondary silver characteristic rays (K type) 

 used instead. These were excited in the usual manner, and 

 the best arrangement for the greatest homogeneity was 

 determined by obtaining a series of absorption curves in 

 aluminium. Using a bulb with a platinum anticathode, it 

 was found best to have an alternative spark-gap of 2*7 cm. 

 (between points), a thin plate of silver (99*9 per cent., 

 •075 mm.), and a filtering screen of silver foil ('026 mm.). 

 The bulb was placed in a large lead-lined box directly above 

 the radiator, which was again in a small lead box from which 



* Communicated by Prof. Sir J. J. Thomson, O.M., F.R.S. 



f Barkla and Simons, Phil. Mag. Feb. 1912 ; Barkla and Philpot, 

 Phil. Mag. June 1913. 



\ H. Moore, Proc. PIiys. Soc. June 1915 ; also E. A. Owen, Proc. 

 Roy. Soc, xciv. A, 1918. " 



