478 



REPORTS ON THE STATE OP SCIENCE. 



molecules before and after the chemical change in the wave, C^ and C„ 

 = the mean specific heats of the products at constant pressure and 

 volume respectively, h = the total heat generated in the wave, and 

 t = the initial temperature (abs.) of the mixture exploded. From the 

 fact that the dilution of electrolytic gas (2H 2 + 2 ) with oxygen 

 lowers its rate of explosion a little more than a corresponding dilution 

 with nitrogen, Chapman considers it improbable that there is any 

 appreciable dissociation of steam in the wave. He assumes that the 

 molecular heat of steam rises more rapidly with temperature than that 

 of a diatomic gas, and that the molecular heats of oxygen, hydrogen, 

 nitrogen, and carbon monoxide may for all practical purposes be con- 

 sidered as equal at any given temperature. Selecting some seventeen of 

 Dixon's found rates of explosion, he has calculated by means of his 

 formula the corresponding molecular heats and temperatures, arriving 

 at the following results for Co at intermediate temperatures by inter- 

 polation : — 



Temperature 

 „ | Steam . 



\ Diatomic gases 



With the aic 1 of this series of numbers he proceeded to apply his formula 

 to the calculations of the rates of explosion of some forty other mixtures 

 investigated by Dixon, finding in all cases close agreement between the 

 found and calculated values, of which the following may suffice as 

 examples : — 



A characteristic feature of detonation is the extremely short duration of 

 chemical action and subsequent rapid cooling of the products, as compared 

 with ordinary combustion. Some years ago the writer, working in con- 

 junction with Bevan Lean, under Professor H. B. Dixon's direction, 

 found by a photographic method that the duration of luminosity in each 

 successive layer of gas in the detonation of electrolytic gas is certainly less 

 than -g^j -, second, 1 a much shorter interval of time than was required to 

 shatter a tube of thin glass attached to the end of the explosion coil used. 

 This tube, although invariably smashed by the force of the explosion, 



1 Brit. Assoc. Report, 1892. 



