Chemical Combination of Gases. 251 



Combination of Hydrogen and Iodine at 440° C. 



Ratio of free hydrogen to 

 Proportion the total quantity of hydrogen. 



of H and I. , ^ N 



Observed. Calculated. 



H + I . . . . -240 -240 



H + -784I .... -350 -342 



H + -527I .... -547 519 



H + -258I .... -774 -750 



Here the agreement between theory and experiment is as 

 close as could be expected. 



We also find from the experimental results that 



£m = 40 . L 



hh T 2 



We have just seen that t 3 2 T l r B /t 1 t 2 T2 2 can be determined by 

 observations made when things have settled into a state of 

 equilibrium ; we shall require, however, other observations to 

 determine the tfs and the r's separately. Let us suppose 

 that the dissociation is produced by some external agency ; 

 then tx will be the same for hydrogen alone as for hydrogen 

 and chlorine mixed, and we may suppose that t x and t 2 have 

 been determined by experiments on hydrogen and chlorine 

 separately by one of the methods of § 1 . Suppose that we 

 have an arrangement for taking the hydrochloric acid away 

 as soon as it is formed (this may be done by absorbing it 

 by water, as in Bunsen's and Roscoe's experiments on the 

 combination of hydrogen and chlorine exposed to the action 

 of light), and that equal quantities of hydrogen and chlorine 

 stream into the vessel where combination occurs at such a 

 rate as to keep the pressure there constant; then if v be the 

 number of molecules of either hydrogen or chlorine which 

 flow into the combination-chamber 'in the unit of time, 

 instead of equation (7) we have the following set of equa- 

 tions, the notation being the same as before: — 



m 2 n 

 mp 



T 2 



so that / . n\i . q\ 4?' 2 t 2 2 



S2 



