Mr Horton, The emission of positive rays, etc. 329 



The emission of positive ray s from heated phosphorus com^pounds. 

 By Frank Horton, M.A., St John's College. 



[Bead 25 October 1909.] 



Prof. Sir J. J. Thomson has shown that certain salts when 

 heated give- rise to a large positive ionisation*. Of the salts he 

 experimented with the greatest effect was given by phosphates, 

 and of these aluminium phosphate was found to be the most 

 active. From this salt at a red heat Sir J. J. Thomson found 

 that the emission was so great as to be easily measured with a 

 galvanometer. The following experiments were made with the 

 object of discovering whether there was any connection between 

 this phenomenon and the "anode rays" of Gehrcke and Reichen- 

 heim. These experimenters have found -f* that when certain salts 

 are used as anodes in a vacuum tube they give off positive rays 

 which proceed at right angles to the surface of the anode and 

 behave in a manner completely analogous to that of cathode rays. 



1. 



A, anode. K, cathode. 



These anode rays consist of positively charged particles of atomic 

 dimensions moving with a velocity of about 10'' cms. per sec. 

 Spectroscopic evidence has proved them to consist of atoms of 

 the metal contained in the salt anode. Gehrcke and Reichenheim 

 found that anode rays were most freely emitted by the halogen 

 salts of the alkali metals, and they consider that in general the 

 most suitable salts to use as anodes are those which are easily 

 fusible and easily dissociated by heat. The halogen salts experi- 

 mented on by Sir J. J. Thomson were found to give a small excess 

 of positive electrification when heated, but nothing nearly so great 

 as that given by the phosphates. 



Aluminium phosphate was the salt first used in the present 

 experiments, and tubes containing this were employed as anodes 

 in an apparatus (see Fig. 1) similar to that described by Gehrcke 



* J. J. Thomson, Proc. Camb, Phil. Soc. Vol. xiv. p. 105. 



t Gehrcke and Reichenheim, Ann, der Phys. xxv. p. 861, 1908. 



VOL. XV. PT. IV. 22 



