322 REPORTS ON THfi STATE OF SC!IE^fCE. 



estimated the loss of heat by prolonging this curve backwards, as showfl, 

 They assumed, in fact, that the pressure given by the point B was that 

 which would ultimately have been reached had the explosion taken place 

 in a vessel with walls impervious to heat. 



It is difficult to justify this procedure on a priori grounds ; the only 

 satisfactory justification is to show, by independent evidence, that it 

 leads to correct results. The main object of this section of the Report 

 is to examine such evidence as there is of this kind, to point out the 

 defects in it, and to suggest experimental methods by which they could 

 perhaps be remedied. 



In so far as the heat-loss and the departure from equilibrium are 

 dependent on surface phenomena, a definite estimate of their amount 

 can be obtained by a comparison of explosions of the same mixture in 

 vessels of different sizes. 



Many years ago Berthelot tried this experiment, firing hydrogen and 

 oxygen, in explosive proportions, in vessels of 300 c.c. and 4000 c.c. 

 respectively. It is stated that the pressure reached was very nearly the 

 same, which would show that such part of the cooling and other corrections 

 as depends on the surface of the vessel is small in the case of this mixture. 



Materials for a more accurate comparison are to be found in the 

 extensive researches of Mallard and Le Chatelier, and of Langen. The 

 French^ experimenters worked with a cylindrical vessel 17 cm. x 17 cm., 



„ . surface 



whereas Langen used a sphere 40 cm. diameter, ihe ratio ^.^^^^^ 



was 2*3 times as great in the first as in the second case. 



The following table shows the results obtained in two instances, in 

 each of which the composition of the mixture was practically identical 

 in the two sets of experiments :— 



IIo is the pressure reached in the explosion in atmospheres after 

 correcting for cooling in the manner described above, when the initial 

 temperature is 0° C. The cooling correction, or excess of the pressure 

 at B (fig. 3) over that at A, is shown in the last column. Figs. 4 and 5, 

 which are taken from Langen's paper, show a comparison between the 

 curve adopted by Langen, as representing the results of his experiments, 

 and Mallard and Le Chatelier's observations. 



On the whole the agreement between the two sets of experiments ia 

 very fair, and the deviations are not such as to suggest that any very 

 great error has been made in estimating such part of the corrections for 

 heat-loss or for unburnt gas as depend on the surface of the vessel. If, 

 for example, Langen were, on the average, 4 per cent, out from this 

 cause, Mallard and Le Chatelier would be 9 per cent, out, and would 

 differ by 5 per cent, from Langen. Differences of that amount do 

 occur, but they do not seem to be systematic. Further experiment of 

 the same kind on vessels with a greater difference of size but of similar 

 geometrical form is, however, desirable, 



