444 Professor Harold B. Dixon [June 12, 



of ignition of carbonic oxide and oxygen was less tlian 1 metre per 

 second. Bunsen applied these results to the rate of explosion of 

 gases in closed vessels, and his results were accepted without cavil 

 for fourteen 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 of carbonic oxide and oxygen 

 travelled in a long eudiometer too quickly to be followed by the eye. 

 Mr. A. V. Harcourt, in his investigation of an explosion which 

 happened in a large gas main near the Tottenham Court Eoad 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 noticed 

 the rapid increase of velocity as a flame of carbon bisulphide with 

 nitric oxide travelled down a long glass vessel ; and shortly after- 

 wards I attempted to measure the rate of explosion of carbonic oxide 

 and oxygen by photographing on a moving plate the flash at the 

 beginning and end of a long tube. The two flashes appeared to 

 be simultaneous to the eye, but no record of the rate was obtained, 

 for the apj)aratus was broken to pieces by the violence of the 

 explosion. 



In July 1881 two papers appeared in the ' Comptes Eendus,' one 

 by M. Berth elot, the other by MM. Mallard and Le Chatelier. 

 Both papers announced the discovery of the enormous velocity of 

 explosion of gaseous mixtures. Other papers quickly 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 which remains constant, however long the column 

 of gases may be. This maximum M. Berthelot states to be indepen- 

 dent of the pressure of the gases, of the material of the tube, and of 

 its diameter above a small limit. 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 mix- 

 ture of gases at the maximum velocity. 



"While Berthelot, associated with Vieille, was 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) tbat the flame either goes out 

 altogether, or that the rest of the gas detonates with extreme velocity. 

 Again, when a mixture of gases was fired near the closed end of the 



