500 REPORTS ON THE STATE OF SCIENCE. 



at comparatively low temperatures. In illustration of their results may 

 be quoted the following remarkable instances of direct ' hydrogenations ' 

 effected by merely passing a mixture of the substance in question with 

 hydrogen over finely divided and freshly reduced nickel. In this way 

 olefin ic hydrocarbons are convertible into the corresponding paraffins at 

 160°; benzene yields cyclo-hexane ; nitro-benzene may be reduced to 

 aniline ; whilst nitro-methane is convertible into methylamine at 150° to 

 180°, and into methane and ammonia at 350°. Finally, a mixture of 

 carbon monoxide (1 vol.) and hydrogen (3 vols.) may be completely 

 transformed into methane and steam at 250°. 



In the present imperfect state of our knowledge any suggestion 

 which may be put forward as to the action of hot surfaces in rendering 

 such gases as hydrogen or carbon monoxide ' active ' must be considered 

 as quite tentative. Several facts, however, point to a possible connection 

 between surface combustion and the emission of charged particles by hot 

 solids. In 1903 H. A. Wilson 1 discovered that hydrogen has an enor- 

 mous influence upon the negative leakage from a clean platinum wire at 

 high temperatures; thus at 135°, for a given potential difference, the 

 leakage in hydrogen at 0"014 mm. pressure was found to be no less than 

 25,000 times greater than in air ; it was also proportional to the pressure 

 and depended upon the hydrogen actually occluded by the metal. These 

 observations have since been confirmed by O. W. Eichardson 2 — who, 

 however, finds that the leakage consists of two parts, one propor- 

 tional to the pressure (due to ionisation by collisions) and the other 

 independent of it; he takes the view that hydrogen does not act per se, 

 but only indirectly by producing some change in the surface of the metal. 



Sir J. J. Thomson has found that the rate of emission of negative 

 corpuscles by alkali metals at ordinary temperatures is greatly increased 

 whilst they are absorbing hydrogen, 3 and F. Horton has proved that the 

 negative leakage from hot lime is much greater in hydrogen than in air. 4 



With regard to the catalytic combustion of hydrogen in contact 

 with metallic surfaces P. J. Kirkby, in experimenting upon the effects 

 of electrically heating a platinum wire to circa 275° in electrolytic gas at 

 pressures under 40 mm., concluded that it is ' probably connected with 

 the corpuscular discharge which is known to be emitted by platinum.' s 

 Finally, it has recently been proved in the writer's laboratory that gold 

 p;auze immediately acquires a negative charge on its inducing the surface 

 combustion of either hydrogen or of carbon monoxide. All these facts 

 point to the necessity of a systematic investigation of the electrical con- 

 dition of heated surfaces during catalytic combustions as a preliminary 

 1o a better understanding of the phenomenon. 



1 Phil. Trans.. A. 202, 243. 2 Ibid'., 1908, A. 207, 1. 



B Phil, Mag., 1005, 6th series, 10, 584. 4 Phil Trnvs., 1908, A. 207, 149. 



5 Phil Mag.. 1905, 6th series, 10, 467. 



