Chemical Combination of Gases. 253 



§ 4. Hitherto we have only considered the combination of 

 two monad elements ; the same theory will, however, apply 

 to the combination of any two elements of the same quanti- 

 valence. We shall now go on to consider the more complex 

 case of the combination of a dyad element with a monad, 

 when two atoms of one are combined with one of the other; 

 as a typical case we may take water, H 2 0. Here the question 

 arises, does the combination consist in an atom of oxygen 

 uniting with a molecule of hydrogen, or is it necessary that 

 the hydrogen molecule should be itself split up, and that 

 combination takes place when two atoms of hydrogen meet 

 with an atom of oxygen ? We shall suppose that both methods 

 of combination take place, and then, after the investigation 

 is complete, we may deduce either case by giving special values 

 to the constants. 



Let m = the number of hydrogen atoms. 



n — the number of hydrogen molecules. 



p = the number of oxygen atoms. 



q = the number of oxygen molecules. 



r = the number of water molecules. 



M = the total number of hydrogen atoms free and 

 combined. 



N = the total number of oxygen atoms free and com- 

 bined. 



t l = the time the atoms remain together in the hy- 

 drogen molecule. 



i 2 = the time two oxygen atoms remain together in 

 the oxygen molecule. 



t z = the time the atoms remain together in the water 

 molecule before splitting up into a molecule 

 of H and an atom of 0. 



t f 3 = the time the atoms remain together in the water 

 molecule before splitting up into two free atoms 

 of H and an atom of 0. 



— = the time during which a hydrogen atom is free 



from another hydrogen atom. 



— = the time a hydrogen molecule is free from an 

 P oxygen atom. 



— — = the time which elapses before a free hydrogen 



P atom meets simultaneously with another free 



hydrogen atom and an oxygen atom. This time 



will be inversely proportional to mp, since if 



m and p be large, mp is the number of groups, 



