330 INFRA-RED EMISSION SPECTRA. 



SUMMARY. 



The present investigation of infra-red emission spectra had for its 

 aim the study of the region of the spectrum lying beyond 2 {x, which 

 heretofore had never been examined. The question of the presence of 

 emission Hues beyond this point is chiefly of theoretical interest. 



Two classes of radiation have been investigated, viz, the arc between 

 metallic electrodes and the chlorides of the alkali metals in the carbon 

 arc, and the discharge through a vacuum-tube using different vapors 

 and gases. 



It was found, for the arc between metal electrodes, that the oxides 

 emitted a black-body spectrum of sufficient intensity to obliterate any 

 emission lines, if any were present. 



Using the chlorides of the alkali metals, the strong emission lines 

 mapped by Snow were verified, but beyond 2 fx no emission lines could 

 be found. 



The emission spectra of the following vapors and gases were exam- 

 ined in a vacuum-tube; H,0, C^H^OH, H, N, NH3, O, CO, and CO,. 

 Of this number the CoHgOH, CO2, and CO have a very strong emission 

 band at 4.75 /a. 



Nitrogen is the only gas studied which has strong emission lines in 

 the infra-red. The maxima are at 0.75 /x, 0.90 /a, and 1.06 ft. The 

 behavior of these lines is entirely different from the 4.75 ju, band found 

 in CO2 and CO. At a constant current the intensity of the 4.75 ix band 

 increases with the pressure, but never reaches a maximum, becoming 

 asymptotic at 5 to 6 mm. pressure. On the other hand, the nitrogen 

 bands increase in pressure, become a maximum at about 2 mm. pressure, 

 then decrease in intensity with a further increase in pressure, which 

 agrees with observations in the visible spectrum. 



At a constant pressure all lines increase in intensity with increase in 

 current, as found in the visible spectrum. 



Condenser in parallel increased the intensity slightly, due to an 

 increase in the current through the tube. 



The aim in using a vacuum-tube was to avoid oxides. No lines, how- 

 ever, were found beyond 2 /a, except the 4.75 yu. band, which seems to be 

 due to the warming of the gas. Since the intensity of the vacuum- 

 tube radiation is only from -j-^g to gr/oo as great as that of a black body, 

 if there be weak emission lines beyond 6 |U. it would be almost impossi- 

 ble to detect them with our present measuring instruments. 



The emission spectrum of C0H5OH shows that a vapor in a vacuum- 

 tube can emit a continuous spectrum. 



