474 



Oxygen Mixtures. 

 2CO + 2 . 2 metres per sec. 



2H. 2 + 2 . . . 20 

 CS. 2 + 30 a . . 22 

 C 2 H 2 + 2|0 2 . . 200 



It should be noted that for mixtures of the same gas with various pro- 

 portions of air, the initial rate of inflammation attains a maximum when 

 the combustible gas is present in considerable excess of that required for 

 perfect combustion. 



H. B. Dixon's experimental method consisted in photographing the 

 explosion flame travelling along a horizontal tube on a highly sensitive 

 film rotated vertically with a constant high velocity (varying, however, 

 between twenty-five and fifty metres per second in different experiments), 

 the explosion tube being placed at such a distance from the camera that 

 the size of the image was about one-thirtieth that of the flame. In this 

 way it was found possible to analyse the progress of an explosion from 

 its point of origin up to the final attainment of its maximum force and 

 velocity in ' detonation.' The investigation also included the discovery of 

 the wave of ' retonation,' which is thrown back through the still burning 

 gases from the point where detonation starts (a phenomenon also in- 

 dependently discovered by Le Chatelier in 1900), of the effects of collision 

 between two explosion waves, and of the passage of reflected waves 

 through the hot products of explosion. 



The phenomena associated with the development of an explosion in 

 a gaseous mixture, fired in a closed tube by a spark passed between 

 wires a few inches from the closed end, are very clearly shown in the 

 photograph reproduced in fig. 1 (Plate VII.), which is analysed in the 

 diagram fig. 2 (Plate VII.). This photograph was taken during an experi- 

 ment in which carbon disulphide was exploded with a tjuantity of oxygen 

 represented by the expression CS 2 +50 2 . The flame, in starting at the 

 point O, sends out invisible compression waves in both directions along 

 the tube, which travel in advance of the flame with the velocity of sound 

 through the unburnt gases, as represented by the dotted lines O M, O N 

 in the diagram. The flame itself, travelling at first more slowly than 

 the compression waves, traces the curves O A and O B. The compres- 

 sion wave ON, on reaching the closed end of the tube, is reflected back 

 again as N C, and, on meeting the flame (which is still travelling in the 

 direction O A), retards it, and passes thence through the hot and probably 

 still burning gases as the visible wave C D. An instant later it overtakes 

 at D the front of the flame, travelling in the direction O B, thereby 

 accelerating it and increasing its luminosity in consequence of the 

 quickened combustion. The flame then continues to move forward with 

 rapidly accelerated velocity until ' detonation ' is set up at the point E. 

 At this point a strongly luminous wave of compression E G (the 'retona- 

 tion wave ') is sent backwards through the still burning gases, which, on 



