LEWIS. — A NEW SYSTEM OF THERMODYNAMIC CHEMISTRY. 



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The first column gives the pressure, the second gives the concentration 



in mols per liter f - : J, the third gives the activity, also in mols per 



liter, and the fourth gives the ratio of activity to concentration, which 

 for a perfect gas is always unity. The increase in this quotient between 

 200 and 300 atmospheres is interesting, and the whole table shows how 

 little either the pressure or the concentration of a compressed gas 

 is suited to act as a measure of the escaping tendency. 



If instead of determining the activity of gaseous carbon dioxide we 

 desired to determine that of C0 2 in some other phase, for example in 

 a solution of sodium bicarbonate in water at a given temperature and 

 concentration, it would be only necessary to know the pressure or the 

 concentration of carbon dioxide gas in equilibrium with that phase. 

 For the activity there would be the same as in the gas, and the latter 

 could be determined by the above method. 



This, therefore, is a perfectly general method for determining the 

 numerical value of the activity. However, it is to be emphasized that 

 in most cases where the conception of activity is useful, it is not necessary 

 to know the numerical value, Out only the ratio of the activities in two 

 given states. This will be illustrated in another section. 



Influence of Pressure, Temperature, and Concentration upon 

 the Activity of the Constituents of a Binary Mixture. 



The equations in this section will apply not only to a homogeneous 

 liquid mixture, but also to a gaseous mixture, or solid solution, in fact 

 to any homogeneous phase 

 whatever which is composed 

 of the two molecular species, 

 Xi and X 2 . The composition 

 of a binary mixture we shall 

 express, following Ostwald, 

 by the molecular fractions 

 (Molenbruche), Ni and N 2 , 

 so denned that N a + N 2 = 1 . 

 By one mol of the mixture 

 we shall mean that amount 

 which contains Nx mols of 

 Xi and N 2 of X 2 . Later, in dealing with mixtures of more than two 

 constituents, the fractions Nx , N 2 , N 3 , etc., will be similarly defined, 

 so that Nx + N 2 + N 3 + . . . = 1. 



The influence of pressure upon the activity of either constituent of 



Figure 1. 



