﻿Ignition of Gases by Sudden Compression. 105 



The theoretical values given in this table are represented 

 by the dotted curve in fig. 9, the experimental results 

 (Table V.) being shown by circles. The close agreement 

 between experiment and theory is obvious ; it is, indeed, 

 closer than could reasonably have been expected in view of 

 the fact that the temperature errors must be estimated as 3 or 

 4 degrees, while the cooling factors are subject to an error 

 of about 5 per cent. The results can, however, leave little 

 doubt of the substantial accuracy of the simple theory 

 worked out above, and the temperature coefficient deduced 

 must be very near the truth. It is of great interest to note 

 that it is of the same order as that of chemical reactions in 

 liquids at ordinary temperature ; for the reaction velocity is 

 approximately doubled for a 3 per cent, rise in absolute 

 temperature. 



XII. The only experimental values given in Tables III. 

 and V. which seem to call for any special comment are 

 those corresponding to experiments A 4 and A 8 . The 

 " delays " found in these experiments were considerably 

 smaller than those expected theoretically. This may be due 

 to the fact that the measurement of very small delays is 

 necessarily somewhat inaccurate with the apparatus used, 

 since the speed of the piston falls off as the compression 

 approaches its maximum. In such cases the lowest ignition 

 temperature is, of course, reached before the piston reaches 

 the top of compression, so that the measured " delays " 

 which are measured from the time of maximum compression 

 tend to be too small. But there is also a curious effect, 

 which is invariably observed in these experiments on the 

 self-ignition of carbon compounds, when the initial tem- 

 perature is high, and the time of explosion short. It is 

 always found that the explosion, though apparently sharp, 

 is not complete, but that a fluffy deposit of carbon is thrown 

 down. This deposition of carbon in an explosion has often 

 been noticed by other workers when ignition is effected by 

 a spark, but it is usually thought to be a consequence of 

 having too little oxygen for complete combustion; in our 

 experiments, however, the oxygen was always in considerable 

 excess. When the minimum ignition temperature is not 

 greatly exceeded, and when therefore the explosion is 

 comparatively slow, combustion is complete, and no carbon 

 deposit is formed. At higher initial temperature, however, 

 one cannot escape the conclusion that the hydrogen is burnt 

 preferentially to the carbon, and that the rate of combination 

 of carbon atoms can be greater than the rate of combination 



