130 Mr. Harold B. Dixon on 



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 " I'onde explosive" was given 

 by Berthelot to the flame when propagated through an 

 explosive mixture 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 : — (i) 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 (depend- 

 ing 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 that the rest of the gas detonates with extreme velocity. 

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

 end of the tube they found the velocity of the flame 

 regularly increased, as far as their instruments were able to 

 record the rapidly increasing pace. 



Mixtures of coal-gas with air, and of fire-damp with air, 

 show phenomena of the first and second kind. Ignited at 

 the open end of a tube these mixtures burn at a uniform 

 rate for a certain distance, and then the flame begins to 

 vibrate. 



The vibrations acquire greater or less velocity according 

 to the nature of the mixture and the conditions of the 

 experiment ; but the third regime of uniform maximum 

 velocity is not set up. In narrow tubes the explosion soon 

 dies out. 



