PEOFESSOR H. B. DIXOE' OX THE RATE OP EXPLOSION IN GASES. 
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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. 
Cap. II.—Berthelot’s Experiments. 
Berthelot’s experiments were made partly with a tube of lead, and partly witli a 
tube of thick caoutchouc, usually 5 mm. in internal diameter. The rate of explosion 
was determined by making the flame break two strips of thin tin stretched across 
the tube, each carrying a current. The interval between the interruption of the two 
circuits was measured by a Le Boulenge chronograph. The gases were fired by an 
electric spark near one of the interrupters. To ensure the fracture of the strips of tin 
a grain of fulminate was placed in a fold of the metal. The tube was 40 metres long, 
and was supported on a wooden screen in horizontal layers. 
The following are the chief conclusions reached by Berthelot concerning the 
propagation of the explosion-wave in gases :— 
(1) The propagation is uniform. Measurements made in tubes of 20, -‘50, and 
40 metres length show the same velocity for the same mixture. 
(2) The velocity is independent of the material of the tube : the explosion travels 
at the same rate in tubes of lead as in tubes of caoutchouc. 
(3) The velocity is independent of the diameter of the tube above a small limit: 
the explosion travels at the same rate in a tube of 5 mm. diameter as in a tube of 
15 mm. diameter. 
(4) The velocity is independent of the pressure : the explosion travels at the same 
rate when the gas is under a pressure of 560 mm. as it does under a pressure of 
1580 mm. 
(5) The velocity of the explosion equals, or approximates closely to, the mean 
velocity of translation of the molecules at the moment of combination, on the 
supposition that they retain all the heat developed in the reaction. The rates of 
explosion of some twenty different mixtures agree with the theoretical rate calculated 
by the formula of Clausius ;— 
e = 29-354 
where T is the absolute temperature reached in the explosion, and d the density of 
the products of combustion referred to aii-. 
