472 



Prof. H. B. Dixon. On the Movements [June 5, 



to the compression-wave which is propagated as the inflammation 

 spreads from layer to layer. To obtain the mean pressure of the 

 ignited mass of gas they had recourse to a less sensitive Bourdon 

 gauge, and from the pressure-curves so registered they calculated the 

 maximum pressures and temperatures of the explosion. Their results 

 may be summarised in the statement that the maximum temperature of 

 the explosion of moist electrolytic gas is 3350° C, and the mean specific 

 heat of steam between that temperature and 0° is 16*6 (at constant 

 volume), dissociation being very slight, if any, between these tempera- 

 tures ; on the other hand, the mean specific heat of C0 2 rises to 13*6 

 at 2000°, and above this dissociation begins. The simple diatomic 

 gases (0 2 , N 2 , CO, &c.) show a rise of specific heat, though far less 

 marked. 



Berthelot and Vieille (1885) also determined the maximum pressures 

 produced in the explosion of gases, and calculated the maximum tem- 

 peratures. Their results were similar to those obtained by Bunsen, 

 but they attribute the defect of pressure observed not to the inability 

 of the gases to combine at the temperature reached, but to the great 

 increase of the specific heats of the products of combustion. 



On the other hand, Dugald Clerk contended (1886) that in an explo- 

 sion the combustion is never completed instantaneously, and since the 

 burnt gases are cooling while the unburnt are still combining, the 

 observed pressures and temperatures fall short of those calculated for 

 instantaneous combustion. 



Mallard and Le Chatelier were the first to record the movements of 

 the flame in explosions by photography on a moving film (1883). 

 Failing to obtain images of the flame with mixtures such as 2 CO + 0->, 

 they employed CS 2 with oxygen and with nitric oxide. 



"When the gases were ignited by a flame at the open end of a long 

 tube, the flame was propagated along the tube for some distance with 

 a uniform slow velocity. In the case of mixtures of carbon disulphide 

 with nitric oxide, this period of uniform movement is succeeded by 

 oscillations of the flame, which sometimes become of larger and larger 

 amplitude and then die down, and sometimes give rise to the " detona- 

 tion-wave." When carbon disulphide is mixed with oxygen, the pre- 

 liminary period of uniform movement is shorter, and is succeeded 

 immediately by the detonation. 



Mallard and Le Chatelier draw attention to the fact that in these 

 explosions — starting at the open end of a tube — the development of the 

 detonation-wave is not progressive, but always instantaneous. When the 

 mixture was fired near the closed end of a tube, the movement of the 

 flame was uniformly accelerated until the detonation is set up. Their 

 apparatus did not move fast enough to analyse the more rapid move- 

 ment of the flame. 



In 1888 von Oettingen and von Gernet analysed the flame by 



