314 -/. Trowbridge — Spectra of Hydrogen 



scope showed only the line spectrum of hydrogen. One would 

 conclude from this inspection alone that there was pure hydro- 

 gen in the tube. One might also surmise that the oxygen of 

 the water vapor always present on the walls of the glass vessel 

 had combined with the aluminum terminals, setting free the 

 hydrogen which then carried the current. The pressure, how- 

 ever, in the tube increased, and therefore gas must have come 

 from the aluminum. In the exhaustion of X-ray tubes pro- 

 vided with aluminum cathodes much time and long treatment 

 with condenser discharges is necessary to drive ont the gases 

 from this cathode. The principal gas seems, from the experi- 

 ment with ammonia gas, to be oxygen. The same phenomenon 

 is seen in tubes supplied with magnesium terminals, but to a 

 much less extent. It is not seen when the terminals are of 

 copper, iron, silver, platinum or carbon. This behavior of 

 aluminum toward oxygen is very suggestive in regard to the 

 ready passage of the X-rays through this metal. 



I have been unable, with the conditions under which I have 

 worked, namely, the use of very powerful discharges, to obtain 

 the spectra of hydrogen apart from water vapor and hydro- 

 carbons. The study, therefore, of the spectra of hydrogen 

 compels one to carefully study the spectra of the hydrocarbons 

 and that of cyanogen ; for I am forced to the conclusion that 

 the combination of hydrogen with oxygen is a controlling fac- 

 tor in all discharges through rarified gases. The following is a 

 preliminary study of some of these compounds, which is added 

 at this stage of my inquiry to illustrate this theory. When 

 various gases are put in tubes provided with carbon electrodes 

 and these tubes are exhausted to a pressure of from one to two 

 millimeters the resultant spectra are very similar. The follow- 

 ing gases have been studied in the neighborhood of the great 

 H H lines of the solar spectrum : 



Hydrogen 



Oxygen 



Nitrogen 



In the hydrogen tube the only lines that appeared in the 

 region from 4320 to 3200 were : 



4268 very intense 

 3922 faint. 



The tube was very thoroughly heated while it was being ex- 

 hausted. The above mentioned lines do not generally appear 

 with hydrogen in tubes with metallic electrodes; but with a 

 tube with platinum electrodes, filled with hydrogen, and 

 heated for two hours during exhaustion at a temperature of 



