and some of its Compounds. 313 



ance takes place. It is possible to exhaust glass tubes to such 

 a degree by the mere passage of a strong steady current that 

 X-rays begin to manifest themselves. 



When a similar tube, filled with hydrogen with great care 

 and prepared by long heating at a temperature a little below 

 500° C, is submitted to electrical discharges, the water vapor 

 bands become far less pronounced; and the hydrocarbon band 

 at wave length 4315 entirely disappears, while the light of the 

 tube greatly diminishes in brilliancy. The hydrocarbon or 

 cyanogen band at wave length 3884 is present in all the tubes 

 I have employed ; and with whatever gas is submitted to these 

 strong discharges. Strong heating does not cause it to disap- 

 pear, and it seems to be due to carbonaceous matter introduced 

 into the tubes in the process of blowing for I cannot trace it 

 to impurities coming from the pump. Professor Hartley, in a 

 late communication in Nature, has called attention to the con- 

 stant presence of hydrocarbon spectra in Geissler tubes. At a 

 later point in this paper I shall return to a further study of 

 these spectra, due to the combination of hydrogen and nitrogen 

 with carbon. At present I desire to dwell upon the point I 

 wish to make : that all discharges in rarified gases contained 

 in glass vessels are conditioned by the amount of water vapor 

 present ; and that a steady current passes through a gas at 

 comparatively low pressure much in the same manner that it 

 does through an electrolyte. 



In an article on the production of the X-rays by a steady 

 battery current, I dwelt upon the phenomena presented in 

 highly rarified tubes which represent, to my mind, the disso- 

 ciation of water vapor; and 1 will refer again at this point to 

 the phenomena already described. According to this hypothe- 

 sis the rarified water vapor is dissociated at the surface of the 

 anticathode, which is thus greatly heated ; the occluded hydro- 

 gen plays a part in this phenomenon. 



The behavior of large aluminum electrodes in glass vessels 

 filled with ammonia gas is also an interesting example of the 

 dissociation of water vapor. The gas was obtained by heating 

 ammonium chloride, passing it over freshly slaked lime and 

 through drying tubes filled with phosphoric pentoxide. A 

 sufficient amount of ammonia gas was thus obtained for the 

 purposes of spectrum analysis. 



When a large condenser, charged to a difference of potential 

 of twenty thousand volts, was discharged through the rarified 

 ammonia gas — there being practically no self-induction in the 

 circuit, and the main effect, therefore, was due to the pilot 

 discharge — the light of the tube changed from a brilliant white 

 to a rosy red ; and eye inspection with a straight-vision spectro- 



Am. Jour. Sci.— Fourth Series, Vol. XII, No. 70.— October, 1901. 

 22 



