2l8 
FREDERICK BARRY 
viously assigned) ; and it may be measured in a variety of wa;ys, in 
many cases with precision. But a moment's consideration shows us 
that the actual velocity must always depend, not only on the intensity 
of the driving force, but also upon the friction opposed to it, which 
will vary markedly with the conditions under which the change occurs. 
Various well-known phenomena, such as those of delayed transition 
and false equilibrium in general, which comprise many common and 
familiar instances of the long continued, or even apparently permanent 
existence of metastable states, indicate the varying and the very great 
degree in which reaction velocities are thus affected. 
Some of these influences are definitely known. The most impor- 
tant is perhaps viscosity, which varies markedly with change of tem- 
perature, in a manner which can be empirically formulated. There 
must be appreciable delay in the speed of reaction, also, whenever 
molecular orientation must precede combination. Contact catalysis, 
which is always associated with adsorption, often has a marked in- 
fluence; and this is largely influenced in turn by other factors of 
variation — especially in colloidal systems. In such systems, moreover, 
enzyme catalysis and coagulation — both influenced by change in 
acidity, basidity and salt concentration in marked degree — may cause 
similarly undeterminable variation. 
These or other influences summarized in the values of the velocity 
constants modify, in a manner not to be generally formulated, the 
speed of a chemical reaction, and its variability with change of tem- 
ture. They may be, of course, in any special case, not beyond the 
possibility of determination; but their nature is such as to involve 
-many constants characteristic of the interacting substances; while 
their interdependence, which may be in certain homogeneous eqtiilibria 
not difficult to define, becomes in general a very complicated matter 
indeed. 
Thus, the velocity of a chemical reaction, far from being a simple 
function of the temperature, appears upon reflection to be quite the 
reverse. In view of what has been said, it is not a matter of surprise 
-that the velocities of different reactions range from the immeasurably 
slow to the immeasurably rapid, and that their accelerations with 
change of temperature vary widely. Usually this acceleration is very 
great, much greater than it would be if it increased proportionately 
with change in the free energy alone. According to the kinetic theory, 
a rate of chemical combination would be determined by the velocity 
