PROFESSOR H. B. DIXOX ON THE RATE OF EXPLOSION IN GASES. 151 
passage of the blue flame down to the tube can be followed by the eye ; the tube is 
then refilled and screwed on to the end of a few feet of leaden pipe filled with the 
mixture. The test-tube is surrounded by metal gauze and a thick glass cylinder. 
On applying a flame to the open end of the pipe, or passing a spark near the 
extremity, a loud report is heard, and the test-tube is reduced to powder.* The 
explosion-wave in a glass tube produces a brilliant flash of orange light. 
Professor A. Schuster! has drawn my attention to a memoir, by Riemann, on the 
propagation of intense disturbances in gases, and has suggested a mode of calculating 
the momentary j)ressures produced in the explosion-wave from its known velocity of 
propagation, and the density of the unburnt gas. On the assumption that Riemann’s 
theory holds for an explosion, I have calculated, from the observed rates of the wave 
and the densities of the unburnt gas, the pressures existing in the wave in the 
explosion of different gaseous mixtures. In parallel columns I have given the 
“ effective ” pressures as registered in the apjaaratus used by Berthelot for the same 
mixtures. The pressures calculated for the wave are rather more than four times 
larger than these effective pressures. In the third column I have given the calculated 
pressures divided by 4'2. 
The pressure in the wave is given by the equation 
_ 
100 
where tt is the pressure in atmospheres, v the rate in metres per second, and p is the 
weight in grammes of 1 c.c. of the unburnt gas. 
* Professor Dewar has noticed the great violecce with wdiich carbonic oxide and oxygen exj)lode 
under certain conditions. He says : “ Sometimes the explosions were so violent as to break the plate 
closing the end of the tube, though this had resisted the explosions of the hydrogen mixture ; wdiile at 
the other times the wave of explosion passed slowly along the tube.” ‘ Roy. Soc. Proc.,’ April 3, 1884. 
Probably owing to differences in the nature of the electric sparks, the “ explosion-wave” was sometimes 
set up in his tube and sometimes not. 
t See note at end of cap. 
