98 
PROFESSOR H. B. DIXON ON THE RATE OF EXPLOSION IN GASES. 
Thirty-five years ago Bunsen'" described a method of measuring the rapidity of the 
flame in gas explosions. Passing a mixture of explosive gases through an orifice at 
the end of a tube and igniting the gases as they issued into the air, he determined the 
rate at which the gases must be driven through the tube to prevent the flame 
passing back through the opening. By this method he found that the rate of 
propagation of the ignition of hydrogen and oxygen was 34 metres per second, while 
the rate of ignition of carbonic oxide and oxygen was less than 1 metre per second. 
Bunsen applied these results to the rate of explosion of gases in closed vessels: his 
results were accepted without cavil for four and twenty years. 
By 1880 facts began to accumulate which seemed inconsistent with Bunsen’s 
conclusions. For instance, between 1876-80 I had several times observed that the 
flame produced l^y igniting a mixture of moist carbonic oxide and oxygen travelled in 
a long eudiometer too quickly to be followed by the eye. Again, Mr. A. Y. 
Harcouet,! in his investigation of an explosion of coal-gas and air, which happened 
in a large gas main near the Tottenham Court Boad in 1880, was led to the conclusion 
that the flame travelled at a rate exceeding 100 yards per second. In the winter of 
1880-1 I was startled by the rapid increase of velocity and violence as a flame of 
carbon bisulphide with nitric oxide travelled down a long glass vessel. 
In July, 1881, two papers appeared in the '^Comptes Bendus,’ one by M. Berthelot, 
the other by MM. Mallard and Le Chatelier. Both papers announced the 
discovery of the enormous velocity of explosion of gaseous mixtures. Other papers 
(|uickly followed- by the same authors. M. Berthelot made the important discovery 
that the rate of explosion rapidly increases from its point of origin until it reaches a 
maximum wliich remains constant, however long the column of gases may be. Each 
mixture of gases has a definite maximum velocity of explosion. The rate of explosion 
thus forms a new physico-chemical constant, having important theoretical and practical 
bearings. The name “ L’Onde Explosive ” is given by Berthelot to the flame when 
propagated through an explosive mixture of gases at the maximum velocity. 
While Berthelot, associated with Yieille, w-as measuring the rate of the 
explosion-wave ” for various mixtures of gases. Mallard and Le Chatelier 
continued the study of the preliminary phenomena of explosion which precede the 
formation of the “ wave.” They showed by photographing on a revolving cylinder :— 
(1) that when a mixture such as nitric oxide and carbon bisulphide is ignited at the 
open end of a tube, the flame travels a certain distance (depending on the diameter 
and length of the tube) at a uniform velocity; (2) that at a certain point in the tube 
vibrations are set up, which alter the character of the flame, and that these vibrations 
become more intense, the flame swinging backwards and forwards with oscillations of 
increasing amplitude ; and (3) that the flame either goes out altogether, or the rest of 
the gas detonates with extreme velocity. Again, when a mixture of gases was fired 
* ‘ Gasometrische Metliodeu,’ 1857. 
t Repoi-t to the Boai’cl of Trade. 
