﻿and its relations with the Pressure. 115 



moment when (the heat of the mixture being a maximum) the 

 dissociation of water corresponding to this temperature presents 

 an obstacle to the complete union of its elements. Adopting 

 the new number 2800°, we see that the part combined or not 

 dissociated of the flame of hydrogen and of oxygen is really 0*50, 

 or half the total mass. 



Bunsen's valve-eudiometer enabled him to investigate the tem- 

 perature of combustion when the total pressure of the oxygen 

 and hydrogen is diminished and is brought below the atmospheric 

 pressure. It is sufficient for this purpose if a certain quantity 

 of an inert gas be added to the explosive mixture. Under these 

 circumstances Professor Bunsen observed that this temperature 

 rapidly decreased in proportion as the partial tension of the ex- 

 plosive gases was made to decrease. Consequently the quantity 

 of matter dissociated, or the tension of dissociation of water in 

 the flame, decreases with the temperature. 



What would take place if we investigated the temperature of 

 combination under a higher pressure than that of the atmo- 

 sphere ? This is obviously shown by Professor Frankland's ex- 

 periments. 



To acquire absolute certainty on this point a striking verifica- 

 tion is required, which may be obtained either by melting pla- 

 tinum in an artificially condensed atmosphere, or by repeating 

 Bunsen's experiments with the valve-eudiometer. 



I am about to commence experiments of this kind ; they will 

 be made in a laboratory with iron walls capable of resisting a 

 pressure of at least three atmospheres — a pressure which the ex- 

 periments made at the bridge of Kehl show is quite innocuous. 



It is easy to understand the practical consequences which may 

 flow from a series of experiments made under pressure with the 

 ordinary combustibles. They lead to a direct trial of furnaces 

 fed with air forced under a pressure equal to the pressure of the 

 vapour in the generator. These furnaces, especially if they are 

 fed with the mineral oils, the use of which is already beginning 

 to be recommended, and which leave no residue — these boilers 

 where the products of combustion compressed to five atmospheres, 

 for instance, would move through the tubes with one-fifth the 

 velocity of our present apparatus, would doubtless enable the sur- 

 face of heating to be considerably diminished. It is owing to the 

 interest that investigations of this kind may have in furnishing 

 naval engineers with the data necessary for calculating the 

 results, that the Emperor has been good enough to order that 

 these experiments be made in the laboratory of the Ecole Nor- 

 male. A large cylindrical chamber capable of holding the ope- 

 rator and his apparatus, and of supporting a considerable pres- 

 sure of air furnished by a steam-pump, will form a laboratory 



12 



