22 
Proceedings of Royal Society of Edinburgh. [sess. 
On the Velocity of Graded Actions. By James Walker, 
Ph.D., D.Sc., University College, Dundee. 
(Read December 6, 1897.) 
The theory of mass action leads to very simple consequences 
when applied to the determination of the velocity of chemical 
processes which take place in homogeneous solution. If the re- 
action is pure and irreversible, the initial concentrations of the 
reacting substances have only to he known in order to obtain an 
expression which shall give for every value of the time (measured 
from the beginning of the reaction) the corresponding extent to 
which the action has taken place, one constant being involved. 
This constant, which is characteristic of the reaction, is called its 
velocity constant, and for a given medium and a given tempera- 
ture is invariable. Enactions have been classified by Van’t Hoff 
into unimolecular, bimolecular, trimolecular, etc., reactions, accord- 
ing to the number of molecules which interact ; and to every class 
there corresponds an equation by means of which the velocity 
constant is determined, the expressions for the constants differing 
from each other in form from class to class. For example, if the 
initial concentration of each of the reacting substances be A, the 
time t , and z the extent to which the action has progressed at the 
end of the time t , then the following expressions will be con- 
stant : — 
) l0 & 
for unimolecular actions. 
for bimolecular actions. 
A-z 
for trimolecular actions. 
2 A 2 (A - zy 
Now a pure reaction must be unimolecular, bimolecular, in 
general n-molecular, and we should therefore expect in any 
particular case that one of the above series of expressions should 
