214 
FREDERICK BARRY 
by a simple case: it v equals the speed of a reaction in which equal 
molecular quantities combine, so conducted that the products are 
removed as soon as formed, we have: 
where Ci, ^2, • • • represent the concentrations of the reacting substances, 
and where k, the velocity constant, is a constant characteristic of the 
system in question, which, in comparison with other similar constants, 
measures relative tendencies to combination. If in a reaction the 
products accumulate, and if none leave the reacting system, then as 
soon as one reaction begins with high velocity, the opposing tendency 
to recombination at once asserts itself. As the one velocity decreases 
in consequence of diminishing concentration of the factors, the other 
increases. At any stage of the process the speed of the reaction will 
be equal to the difference between the two opposed velocities; and 
when the two become equal, dynamic equilibrium will result. Thus, if 
the two velocities be written Vi = kiC^CB ' ' and, V2 = k2C-A'CB' ' ' 
we have for this condition: 
In this formulation (10), K, known as the equilibrium constant, is 
the ratio of the two velocity constants, and is characteristic for each 
isothermal action. It is not necessary to work out the general case, 
which follows by direct application of the principles involved in the 
simpler. Since, moreover, irreversible reactions may be legitimately 
considered to be equilibria very far displaced, we are justified in con- 
sidering the general expression applicable to all reactions. 
The concentration law, first formulated by Guldberg and Waage in 
1867, and experimentally verified both by their own investigations and 
those of previous workers, marked a new epoch in the history of 
chemistry; for it justified completely the method upheld by BerthoUet 
at the beginning of the century: namely, the application of mechanical 
concepts to the study of the age long mystery of chemical affinity. 
The law is of the widest applicability. Its perfect generality is 
demonstrated by' its deduction from the basic assumptions of the 
molecular theory, as well as by its theoretical derivation from the 
V = kCiC2 ' ' ' 
Whence : 
• • • 
(V) 
