1902.] of the Flame in the Explosion of Gases. 473 



means of a rotating mirror. Their photographs reveal, they state, the 

 phenomena immediately succeeding the chemical combustion. 



For although the flame of electrolytic gas appeared intensely bright, 

 its spectrum only gave the sodium and calcium lines, and the most 

 sensitive photographic plates showed " hardly a trace of the process." 

 Failing to photograph the flame itself, the authors added finely 

 divided salts to the tube, and found that the most brilliant pictures 

 were given by cuprous chloride. 



Their pictures show the passage of waves sharply reflected back- 

 wards and forwards from the ends of the tube, and gradually 

 diminishing in intensity and velocity. These visible waves, according 

 to von Oettingen and von Gernet, . are not a picture of the process of 

 combustion itself, but are compression-waves moving through the 

 products of combustion after the explosion is completed. The explosion 

 itself, they say, is quite invisible. Their photographs also show waves 

 running nearly parallel with the primary waves. These secondary 

 waves are particularly referred to as supplying conclusive evidence 

 that successive partial explosions have taken place (starting from the 

 electrodes) exactly as Bunsen imagined. 



In 1884 Liveing and Dewar showed that the flame of an explosion 

 in a glass tube exhibited the spectral lines of sodium and of calcium, 

 and of iron when fired in an iron tube and examined end-on. When 

 metallic salts were introduced in the form of powder, the correspond- 

 ing lines were visible in the spectroscope. They made the interesting 

 observation that the red lithium line was reversed when the explosion 

 was made to travel towards the spectroscope, and they interpreted 

 this to mean that the front of the advancing wave is cooler than the 

 following part. 



I have examined the spectra of many explosion-flames. The light 

 produced by the explosions of electrolytic gas is mainly due to 

 particles knocked from the glass. In the faint continuous spec- 

 trum shown by the flame the calcium lines stand out prominently. 

 When the explosion travels first through a metal tube joined to a glass 

 one in which the flame is photographed, the light is more intense near 

 the junction. One can see the stream of luminous matter carried out 

 of the metal tube. 



The cyanogen explosions, however, give a continuous spectrum 

 crossed by metallic lines and by the characteristic " cyanogen lines." 



The luminous particles, whatever their nature, follow very closely 

 the movements of the gas in which they float. When the spectra of 

 the explosion-flames were photographed " end-on," I have never 

 observed any reversal of a line in the advancing flame. 



2 K 2 



