on the Physical Properties of Gases. 403 



enough, nor exact enough, to enable us to deduce exact 

 numerical results. 



3. In the present paper I first consider the problem, To 

 find the number of blows greater than c, between two sets 

 of moving particles, per unit of time, in unit of volume. 

 This is then applied to find the dissociation at any tempera- 

 ture, and a quadratic obtained, the positive root of which 

 gives the ratio of molecules to free atoms in the gas ; and it 

 is shown that the resulting state of the gas is a stable one. 

 This ratio is used to investigate the relation between the tem- 

 perature and pressure ; and it is shown that Charles's law is 

 not rigorously exact, though within ordinary ranges of tem- 

 perature it is very nearly so ; reasons are also given why 

 for the permanent gases c should be large, compared with 

 the mean blow at ordinary temperatures. Next the specific 

 heats are considered ; and it is proved that for a diatomic 

 molecule, in which the atoms are smooth and spherical, or 

 the energy of rotation of the atoms is unaffected by external 

 causes, the ratio of the specific heats is about 1*4 ; it is also 

 shown that the specific heats are almost rigorously constant 

 at ordinary temperatures. This concludes the present paper ; 

 in what is to follow I intend to discuss the properties of a 

 compound gas of the type HC1. 



4. When we pass to the consideration of a compound gas, 

 even of the simplest form, additional difficulties are introduced, 

 as equations of a high order appear whose algebraical solution 

 is impossible, and from which therefore it will be extremely 

 difficult to deduce general laws. All we seem able to do is 

 to take one or two particular cases, and learn what we can 

 about them. For instance, in the case of a gas of the type 

 HC1, i. e. in which two monatomic gases combine to form a 

 gas whose molecule is diatomic, we get three equations of the 

 second degree between three unknowns. In general, when 

 two gases A and B are mixed together, there will always be a 

 certain proportion of a new gas C whose molecule is com- 

 posed of atoms of A and B, and the proportions of free atoms 

 and molecules of A and B will be altered. When the excess of 

 the number of combinations of free atoms of A with B over 

 the number of molecules of C destroyed in any time is 

 greater than the number of combinations of free atoms of A 

 to form A and of free atoms of B to form B, then the propor- 

 tion of A and B decreases, whilst that of C increases, and we get 

 a chemical change. This will explain why often the mere 

 presence of another gas D will produce a change of A and B 

 into C ; for the action of D on A and B may cause more of 

 their molecules to be broken up than of C, while at the same 



2D2 



