312 



INFRA-RED EMISSION SPECTRA. 



but no emission bands were found. On the contrary the hot cell, after 

 stopping the discharge, gave deflections which were as large as those 

 for the vapor. With water vapor the cell became much hotter than for 

 the other gases. 



A slight trace of water vapor has a great effect in depressing the 

 intensity of the emission lines, as was found on allowing air to enter the 

 tube ; and only after filling the tube several times with air and exhaust- 

 ing it did the air lines at 0.9 ju,, 1.05 fx, and 4.75/^ appear in their usual 

 intensity. 



It will be noticed that the water vapor has no emission lines, which 

 is true of the vapor in the Bunsen or oxy-hydrogen flame. On the other 

 hand, alcohol vapor shows quite a strong emission spectrum from 

 2 to 3 /t. 



Hydrogen (H). 



This sample of hydrogen was generated from Zn -|- HCl and dried 

 in H2SO4 and in PoOg. Its spectrum energy curve is given in figure 

 143, curve a, where the ordinates are deflections in centimeters. 



to 



V) 



' 2 3 4 S 6 



Fig. 143. 



The curve is in two parts, representing different pressures. The 

 red H line gave a deflection of only 2 mm. 



In the region oi i fi there is energy radiated which may be due to 

 slight traces of nitrogen. No emission band is to be found at 4.75 /*. 

 The radiation curve for the hot cell (observations plotted in circles) 

 coincides with that of the gas. 



In the upper part of figure 143, curve b gives the variation of intensity 

 with change in pressure for the region of the spectrum at 0.92 fi. The 



