90 Mr. D. L. Chapman on the 



Company at their Foyers works, alumina, of which the 

 melting-point is certainly above 1700° C. or 1800° C, is 

 dissolved in a bath of melted cryolite at a temperature of 

 about 800° C. So we may imagine melted basalt to be a 

 solvent for felspar, hornblende, mica, and quartz at tempera- 

 tures much below their own separate melting-points ; and we 

 can understand how the basaltic rocks of the earth may have 

 resulted from the solidification of the mother liquor from 

 which the crystalline ingredients of granite have been 

 deposited. 



VI. On the Hate of Explosion in Gases. 

 By D. L. Chapman, B.A. (Oxon.)*. 



THE object of the investigation of which an account is 

 given in this paper is the discovery of formulae to 

 express the maximum rates of explosion in gases and the 

 maximum pressure in the explosive wave. 



The data which 1 propose to use are taken almost entirely 

 from the Bakerian Lecture of 1893, on "The Rates of 

 Explosion in Gases," by Prof. Dixon. The maximum 

 velocities of explosion given below are in all cases those 

 measured by Prof. Dixon or under his direction. Experi- 

 mental conclusions only will be quoted ; for a complete 

 account of the experiments themselves, the reader is referred 

 to the above-mentioned paper, and to several papers which 

 were subsequently published in the ' Journal of the Man- 

 chester Literary and Philosophical Society ' and in the 

 ; Journal of the Chemical Society. 5 



Ignoring for the present all minor details connected with 

 particular cases, which may be more conveniently discussed 

 at a later stage, it is sufficient for our purpose to state at the 

 outset that it has been established that the maximum velocity 

 of explosion, in a mixture of definite composition and at fixed 

 temperature and pressure, has a definite value, independent 

 of the diameter of the tube when that diameter exceeds a 

 certain limit. The relations existing between temperature 

 and pressure and the velocity of explosion are such that an 

 increase of temperature causes a fall in the velocity, whereas 

 an increase of pressure has the reverse effect up to a certain 

 limit, beyond which the velocity remains constant. 



For the suggestion that an explosion is in its character 



essentially similar to a sound-wave, we are also indebted to 



Prof. Dixon ; and there is little doubt that all subsequent 



advance must be made with, this suggestion as the leading 



* Communicated by Prof. Dixon, F.R.S. 



