In the previous paper of the series* on the explosion of isothermic hydrogen-air and carbon monoxide-air mixtures in the theoretical proportions for complete combustion, at an initial pressure of 50 atmosphere it was shown- (1) that whereas in the case of hydrogen-air mixtures, the maximum pressure was always attained in about 0·005 second after the commencement of combustion, and the cooling set in almost immediately thereafter, in the case of the corresponding carbon monoxide-air mixtures, the time similarly taken for the attainment of maximum pressure was about forty times longer (namely, between 0·18 and 0·24 second), and cooling was delayed for quite an appreciable interval, showing that heat energy was still being liberated long after the maximum temperature had been reached; and (2) that the replacement, even in very small properties, of carbon monoxide bu its equivalent of hydrogen in the mixture 2CO+O
2
+4N
2
had an altogether disproportionately large influence in accelerating the rise of pressure on explosion; indeed, it seemed as though the hydrogen had imposed its own character upon the whole course of the Carbon monoxide combustion, even to the extract of suppressing the aforesaid marked evolution of heat after the attainment of maximum pressure.