OF THE FLAME IX THE EXPLOSION OF GASES. 
345 
Many of tlie photogTajjhs show what appears to he a definite inferior limit to the 
riaine in its initial phase, e.g., figs. 46, 59, 63, and 64, as if the tlanie died out 
promj)tly. We attempted to explore the dark region left inside the fiame Ijy passing 
sparks through it. But no effect whatever was j^roduced in the photographs—doubt¬ 
less because the gases were still burning. Indeed, most of the j^hotographs show that 
the i-egion is only comparatively dark. 
I would draw attention to the fact that when no sound-v'aves interfere vfith the 
flame, the retonation-wave is very brilliant; when the flame is crossed several times 
by reflected waves, the light is more evenly distributed. Nos. 63 and 64, taken under 
the same conditions, illustrate this fact. The phenomenon is explained on the 
assumjjtion that in the region traversed by the flame the gases are still hurniug, and 
the sound-waves, when thev enter this reoion, brino’ about an increase in the rate of 
combination. They are, therefore, of the same nature as, but differ in degree from, 
the wave of retouation. The more intense the compression-wave, the more rapid the 
combustion in its path, and the more rapid tlie cooling in its wake. 
The “ kick-off ” which the explosion gets when the gases are fired near one end of 
a tube considerably modifies the initial progress of the flame, especially when this is 
comparatively slow : compare fig. 66 where the spark is passed at the end of the 
tube, with fig. 67, where the spark is passed 4 inches from the end of a siinilar tube. 
For this reason the exj)eriments made on the time required in different gases to 
develop the detonation shov^ed anomalies which only disappeared on firing the gases 
by means of vfires which just penetrated through the stopper at the end of the tube. 
The mean distance in which the detonation is developed in different gases is shown in 
the following table, according to the position of the spark :— 
Tablp: VI.—Distance from the spark at which Detonation is set up. 
Mixture. 
Spark at end. 
Spark 3 iuche.s from end. ' 
■Ilh + 0 ., 
4 feet 
12 inches 
2 H. + 0, 
— 
4 feet i 
GHi - 1 - 0 ) 
— 
16 i 
C.Xo + 0 .> 
81 inclieti 
4 inches 
C.X.,- 1-260 
12 ‘ „ 
10 „ 1 
2 C 0 H 0 + 3 O 0 
D „ 
01 
C 0 H 4 + 2 O 0 
9 „ 
0 „ 
The mixtures most affected by the position of tlie spark among those experimented 
with are those of hydrogen and oxygen. The considerable “run” required before 
the detonation is set up when electrolytic gas is diluted, confirms my previous 
experiments on the rate of explosion of these mixtures. 
The facts established above concerning the initial phases account for the great 
difference observed in the apjiearance of an explosion produced bv a spark in tlie 
VOL. CC.—A. 
Y 
