31G 
PROFESSOR H. B. DIXON ON THE MOVEMENTS 
a further combustion begins, and so on per saltum. These deductions were criticised 
by Berthelot, who pointed out that they assumed the constancy of the specific 
heats of steam and of carbonic acid at high temperatures. 
Buxsen also in the same paper makes the important statement that the rapidity 
Avith which a flame spreads is synchronous with the attainment of the maximum 
temperature and with complete combustion. Having determined the rate at which 
the flame is propagated in j^ure electrolytic gas as 34 metres per second, Buxsex 
finds that the time required to ignite the gas in his pressure-tube from a central 
spark through a radius of 8'5 millims. is 8‘5/34,000 = 1/4000 second. We may 
conclude, he says, that the time u'hich the whole of the gas takes to burn completely, 
and therefore cdso to reach the maximum temperature, is not more than 1/4000 part 
of a second. Buxsex thus identifies the rate of ignition with that of complete 
combustion. I do not know on what grounds Buxsex leased this statement, which I 
have found to be nearly true of the detonation-wave itself {I’onde expdosice of 
Berthelot), hut not of the initial periods of the explosion. 
In 1881 Berthelot"^'" and Le Chatelier! independently discovered the great 
velocity with which the flame travels in gaseous explosions. Berthelot showed 
that this velocity was a constant for each gaseous mixture, and compared the rate of 
the detonation-wave (I’onde explosive) with the mean velocity of the molecules 
jiroduced by the combustion before they had lost any heat. In the Bakerian Lecture 
for 1893 the author showed that Berthelot’s theory did not account for many 
observed rates of explosion, and put forward the view that the “explosion-wave” 
(now called the detonation-wave) travelled with the velocity of sound in the burning 
gases. Using the rates determined by the author, D. L. Charm ax has argued that, 
if the detonation-wave is of a permanent type, an equation can be deduced from 
IIiEMAXx’s formula by which the rates of explosion can be calculated if the specific 
heats are known, and vice versa. The rate of the detonation-wave may therefore be 
utilised, according to Chapmax, to determine the specific heats ol gases at very high 
temperatures. 
In 1883 Mallard and Le Chatelier§ published their researches on the com¬ 
bustion of gaseous explosive mixtures. They were the first to study the movements 
of the flame by a jihotographic method, of which I will speak more fully later on. 
In order to measure the pressures produced in the explosion. Mallard and 
Le Chateiter at first emploved a very delicate Deprez indicator connected with the 
explosion bomb. A s]/ring could he screwed up against the piston so that a certain 
pressure was required to move it. A thin metal tongue attached t<.) a cord and 
weight was held in its place by the pistoii-rod ; if the pressure on the piston equalled 
* ‘ Comptes Rendu.s,’ vol. 93, p. 18. 
t ‘Comptes Reiiclus,’ vol. 93, p. 145. 
1 ‘ Phil. .Mag.,’ Jail., 1899, p. 90, 
§ ‘Annales ties INlines ’ (8th-spries), vol. 4, 1883. 
