394 EXPLOSIVE GASES AND DETONATING GASEOUS MIXTUKES. 



This is also a question in which there intervene, at the same 

 time, the quantities of heat liberated, the specific heats of the 

 products of combustion, and those of the gases in excess with 

 which these products are mixed. The variation of the specific 

 heats of the compound gases with the temperature enters 

 then into consideration here. If this were not the case, it would 

 always be easy to calculate d priori the temperature limit. 

 We will cite various facts respecting the latter temperature. 



14. Temperature of inflammation. This temperature, which 

 corresponds to the minimum of work required to produce the 

 reaction, presents a certain amount of interest as regards appli- 

 cations. It has been frequently studied since the time of 

 H. Davy. On this point, the following are the most recent 

 data, due to Mallard and Le Chatelier 1 : 



2 vols. H + 1 vol. 

 1 H + 2 



1 air + 2 H 



2 air + 1 



M , , cm. ~r JL jj o-j. .. ... *ju\j 



1 ,,0+2 H + 3vols.C0 2 ... 560 590 



1 ,,0+5 CO 



... 550 to 570 



... 530 



... 530 570 



550 



630 650 

 650 



650 660 



.0 



1 ,,0+2 ,,CO 



2 ,,0+1 CO 



1 ,,0+2 CO + 3 vols. C0 2 ... 700 715< 



2 air + 1 CO + 3 C0 2 ... 715 725 



nil PIT (650 explosion 



58 l bil * \600 slow combustion 



1 +2 ,,CH 4 650 to 660 



1 ,,CH 4 +9 air ... ... lower than 750 



It is remarkable how the ignition temperature of detonating 

 mixtures formed by the association of oxygen either with 

 hydrogen, carbonic oxide, or with methane, is but slightly 

 modified by the introduction of even a considerable volume of 

 foreign gases. The same happens at least as long as the limits 

 at which the mixture ceases to burn are not approached. 



Nevertheless, the addition of an equal volume of carbonic 

 acid has a greater influence on carbonic oxide than on hydrogen, 

 as if the very products of the combustion of the mixture 

 exercised a special influence on the ignition temperature. 



The authors also observed that there exist very notable 

 differences between the different intervals of time required to 

 ignite a gaseous mixture brought to a given temperature. Thus 

 the mixtures containing hydrogen or carbonic oxide ignite im- 

 mediately, whilst a certain time is required for the mixtures of 

 methane with air or oxygen. Hence it is that a bar of iron 

 when brought to a red heat does not ignite these mixtures, 

 since the gases escape before having been subjected to the 

 influence of this temperature for a sufficient time. These 



1 " Comptes rendus des stances de TAcade'mie des Sciences," torn. xci. 

 p. 825. 



