Chemical Combination of Gases. 263 



gases. In other words, the proportion of water-vapour to 

 carbon dioxide was found to be from 4*0 to 6*4 times as great 

 as the. proportion of hydrogen to carbon oxide in the residue 

 unburnt. Hence relatively more hydrogen than carbon oxide 

 is burnt in all cases ; the affinity of oxygen for hydrogen is 

 greater than for carbon oxide. 



" The variability in the coefficient of affinity is due to the 

 circumstance that the physical conditions of the reaction vary 

 with the relative quantities of oxygen present. With equal 

 quantities of oxygen the coefficient remains constant, not only 

 when the proportion of hydrogen to carbonic oxide is altered, 

 but also when the unconsumed portion of the combustible 

 gases is replaced partially or entirely by an indifferent gas of 

 similar physical character, such as nitrogen, although the 

 proportion of unburnt gases to products of combustion varies 

 in both cases." 



§ 7. The next case we shall consider is when three atoms 

 of one element A unite with one of another element B to form 

 the compound which we shall denote by A 3 B. This case is 

 more complicated than any of the previous ones when the 

 combination could always be supposed to take place by an 

 atom or molecule of one substance uniting with an atom of 

 another. We may make several hypotheses about the way in 

 which the compound A 3 B may be formed. 



1. We may suppose that there is, in addition to free atoms 

 and molecules of A, a very small number of triplets; this 

 number may be supposed to be very small compared with 

 the number of molecules or even of free atoms of A. We 

 may then suppose that the molecule of the compound A 3 B is 

 formed by one of those triplets combining with an atom 

 of B. 



2. We may suppose that the molecule of A 3 B is formed 

 by an atom and a molecule of A meeting simultaneously with 

 each other and with an atom of B. 



3. We may suppose that three free atoms of A meet 

 simultaneously with each other and with an atom of B. 



We shall investigate the consequences of each of these 

 hypotheses. Let us begin with the first hypothesis. 



Let m = the number of atoms of A. 



n = the number of molecules of A. 



p = the number of triplets of A. 



q = the number of atoms of B. 



r = the number of molecules of B. 



s = the number of molecules of the compound A 3 B. 



