

EXPERIMENTAL KNOWLEDGE OF THE PROPERTIES OF MATTER. 495 



of bodies in tlie gaseous state. And this is the case in spite of very- 

 important -work in this dii'ection done in recent years, and in which the 

 range of temperature has been extended enormously ; yet as the results 

 of these experiments throw light on properties of bodies at high tempera- 

 tures in the state of gas, and give a new method of investigating specific 

 heats at very high temperatures, they cannot be passed over. 



The investigations referred to are those of Mallard and Le Chatelier 

 on the one hand, and on the other those of Berthelot and Vieille ; and the 

 method of investigation — which was not directed wholly nor even mainly 

 to the determination of specific heats — was that of exploding explosive 

 gaseous mixtures in a closed spherical or cylindrical metal reservoir, the 

 mixture being exploded alone in some experiments, and in others mixed 

 with varying quantities of one of the two gases of the explosive mixture, 

 or of some other gas ; by an explosive mixture being here meant a mix- 

 ture of two gases in the proportions in which they react to produce the 

 explosion. So far as these investigations are concerned with specific heats 

 of gases, it is evident that these are specific heats of constant volume. 



Investigations of Mallard and Le Chdielier. 



It is impossible to do justice to the work either of Mallard and Le 

 Chatelier, or of Berthelot and Vieille, in reference to specific heats of 

 gases as deduced from their experiments without an elaborate digest of 

 their work on explosions ; it will suffice the purpose of this paper to give 

 a very brief summary of results. The complete work of Mallard and Le 

 Chatelier on the ' Combustion of Gaseous Explosive Mixtures ' is pub- 

 lished in the ' Annales des Mines,' 1883, ' Memoires,' t. iv. pp. 274-568, 

 the scope of the communication being (p. 275) the determination for 

 the different gaseous mixtures studied of — - 



1. The conditions necessary to the production of quick combustion, i.e., 

 the temperature of ignition. 



2. The rate at which inflammation started at a point propagates itself 

 in a gaseous mixture, and in general the circumstances which characterise 

 this propagation. 



3. The pressure which is produced in a close vessel in consequence of 

 the combustion of the gaseous mixture which is enclosed ; whence one can 

 deduce the laic of cooling of hot gases situated in a cold enclosure ; the 

 temperature produced by the combustion ; and finally the nature of the 

 variations which a very high temperature makes in the specific heats of 

 gases. 



Each of these three parts is the object of a special memoir in this 

 volume. 



The Apparatus used. 



At first Mallard and Le Chatelier used a modified and enlarged form 

 of eudiometer, -such as was used byBunsen in his experiments ' but with 

 a Deprez indicator to give the maximum pressure in each experiment ; 

 the eudiometer was provided with platinum wires between which an elec- 

 tric spark passing exploded the mixture of gases, and the maximum 

 pressure due to the explosion was recorded. It was soon found, however, 

 that explosions in such an apparatus gave irregular results from which no 

 certain conclusions could be drawn ; for explosions in narrow tubes gave 



' Pogg. Ann. t. cxxxi. 1867, p. 161 ; and Ann. Chim. (i), t. xiv. 1868, p. 446. 



