248 Mr. J. J. Thomson on the 



We find, in the same way as before, that for PC1 5 at 137° C. 

 and under a pressure of 243 millim. of mercury the free 

 time is about *26 times the paired time. 



§ 3. In the cases we have hitherto considered only three 

 systems of particles were present, viz. the molecules of A, 

 B, and C. The next case we shall consider is one which is 

 well illustrated by the combination of hydrogen and chlorine; 

 in this case we have five systems of particles — the atoms and 

 molecules of hydrogen, the atoms and molecules of chlorine, 

 and the molecules of hydrochloric acid. We proceed to 

 investigate this case, using the same principles as in the 

 former. 



Let m = the number of hydrogen atoms. 

 n as the number of hydrogen molecules. 

 p = the number of chlorine atoms. 

 q = the number of chlorine molecules. 

 r = the number of hydrochloric-acid molecules. 

 t x = the time two hydrogen atoms remain paired 



together in the hydrogen molecule. 

 t 2 = the time two chlorine atoms remain paired 



together in the chlorine molecule. 

 t$ = the time a hydrogen atom is paired with one of 



chlorine in the hydrochloric-acid molecule. 



— = the time during which a hydrogen atom is free 

 m from another hydrogen atom. 



— = the time a hydrogen atom is free from a chlorine 

 P atom. 



T§ aa ihe time a chlorine atom is free from another 

 V chlorine atom. 



M = the total number of hydrogen atoms, whether 

 free or in combination with other atoms. 



N sb the total number of chlorine atoms, whether free 

 or in combination with other atoms. 



Then, as in § 2, we have the following equations: — 



