Chemical Combination of Gases. 245 



This case is exactly the same as the dissociation of an elemen- 

 tary gas which we considered in § 1. M. Friedel (Bulletin 

 de la Society Chimique y 1875, p. 160, 1876, p. 241, quoted by 

 M. Lemoine, Annates de Chirnie et de Physique, 5 me serie, 

 t. xxvi. p. 324) has made a series of investigations on the com- 

 bination of oxide of methyl with hydrochloric acid; this com- 

 bination is a case of the kind we are considering, as in this 

 combination one molecule of oxide of methyl combines with 

 one molecule of hydrochloric acid. Let us first compare the 

 results obtained by M. Friedel at different pressures with the 

 results given by equation (6), which may be written 



(M- P r=®p, 



where II is the pressure expressed in atmospheres; we suppose, 

 as before, that the collisions do not affect the dissociation. 

 The constant is determined by making the calculated and 

 observed values ofp agree at the pressure of one atmosphere. 



Dissociation of the Compound of Oxide of Methyl and Hydro- 

 chloric Acid at different temperatures. 



Pressure Value of m j M. 



expressed in ( A N 



atmospheres. Calculated. Observed. 



•882 -898 -876 



1 -860 -860 



1-118 -847 -843 



1-447 -790 -815 



Though the observed and calculated results agree tolerably 

 closely, yet the differences between them, considering the 

 comparatively small range of pressure, seem greater than can 

 be accounted for by errors of experiment, and seem to suggest 

 that in this case the collisions may slightly affect the dissocia- 

 tion. 



From these experiments we have 



tM= 5>28 



at the pressure of one atmosphere ; but at this pressure 

 m/M = *86, so that 



