OF THE FLAAJE IN THE EXPLOSION OF GASES. 
319 
little doubt that it really exists. Regnault and Wiedemann both found a distinct 
increase at constant pressure between 100° C. and 200° C. I have lately, in con¬ 
junction with Mr. F. W. Rixon, determined the specific heat of carbonic acid at 
constant volume at 100 ° C., 200 ° C., 300° C., and 400° C., and find a steady rise in 
the constant.'"' On the other hand, the facility with which carbonic acid breaks up 
under the influence of electric discharges indicates that, as its temperature is raised, 
work is done in loosening the chemical bonds—work which Berthe lot calls “ le 
travail de desagregation moleculaire qui precede la decomposition.” Of the fact ol 
the jiartial dissociation of carbonic acid and steam at the temperature of the detona¬ 
tion-wave, Mr. H. W. Smith and I have found direct proof in the unburnt gases 
left on cooling, t 
Liveing and DewarJ showed in 1884 that the flame of an explosion of gases in a 
o'lass vessel exhibited with marked brightness the lines of sodium and of calcium. 
When the explosion ot electrolytic gas was made to pass along an iron tube about 
3 feet long, closed at one end by a jilate of quartz, a spectroscope jilaced in a line 
with the axis of the tube revealed the fact that the light was largely due to iron 
lines. When metallic salts in the form ot powder were introduced into the explosion 
tube, the corresponding lines were visible in the spectroscope. These experiments 
showed how quickly the ignited gases could detach and volatilise solid matter from 
the side of the tube. But as i-egards the nature of the detonation-wave itself, the 
most interesting observation made by Livjhng and Dewar was the reversal of the 
red lithium line when the explosion was made to travel towards tlie spectroscope. 
The natural interpretation of this reversal was that “ there are gradations of tem¬ 
perature in tlie flame, and that the front of the advancing wave of explosion is 
somewhat cooler than the following part.” I woidd observe on this conclusion tliat 
in the many hundreds of photographs taken Iw me, the front of the detonation-wave 
is always shown as exceedingly sharp, and that probably the reversal observed was 
due to the wave reflected back from the quartz plate. 
The light produced by the explosions of electrolytic gas is mainly due to particles 
knocked from the glass. In the faint continuous spectrum shown by the flame, the 
calcium lines stand out prominentlv. When the explosion travels first througli 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, as in figs. 23 and 42 (lead) and 39 (copper). 
The luminous particles, whatever their nature, follow very closely the movements 
of the gas in which they float. 
The cyanogen explosions gave a continuous spectrum crossed by metallic lines and by 
the characteristic “ cvanogen lines.” 
* ‘Brit. Assoc. Eeport,’ 1900, p. 697. 
t ‘ Manchester Memoirs,’ 1S89, p. 2. 
I ‘Koy. Soc. Proc.,’ vol. 36, p. 471. 
