70 Prof. Liveing, On the Influence of [Feb. 14, 
alcohol the whole liquid becomes filled with little bubbles of air 
which rise, not from the surface in contact with the containing 
vessel, but, from all parts of the interior of the mass. It looks as 
if the surface tension between water and alcohol being much less 
than between water and air, the air was rolled up into bubbles in 
all parts of the liquid, just as it is rolled into bubbles on a metal 
plate wetted with water. If a mixture of alcohol and water is 
mixed with a very strong solution of potassium earbonate the 
liquid becomes turbid with drops of alcohol which are formed 
exactly in the same way as the bubbles of air. The surface 
tension between water and the solution of potassium carbonate is 
less than between alcohol and the solution of potassium carbonate 
and the alcohol is rolled into drops according to the laws of 
capillary action. 
Now the surface tension of water containing oxygen in solution 
will, in general, be different from what it is when the water is free 
from oxygen. Moreover it will be different, in general, where it is 
in contact with different substances; it may be greater for some 
and less for others. Also the presence of even minute quantities of 
acid or alkali will sensibly affect it, at least where it comes in con- 
tact with some substances. 
Now surface tension is a form of potential energy, and by the 
laws of mechanics the several substances coming in contact must 
tend to arrange themselves so that this potential energy may be a 
minimum, 
This principle appears to me to be one of wide application in 
chemistry, but hitherto neglected. Whenever the products of a 
chemical change are such as will produce a diminution of surface 
tension, there is a tendency towards that change ; and this tendency 
will become effective if, on the whole, the transformations of 
energy by the alterations of surface tension and of chemical com- 
bination result in a degradation. Hence if we have a solution in 
water of some substance A in contact with some solid S, then if 
the surface tension between the solution and S is diminished by 
increasing the proportion of A in the solution, there will be an 
excess of A drawn into the film in contact with S. On the other 
hand, if pure water have less surface tension than the solution of 
A where it is in contact with S there will be an expulsion of A 
from the film in contact with S. This is not pure speculation. 
We have tolerably conclusive proof that this kind of action does 
take place. It is an old observation that when an aqueous solution 
of acetic acid is filtered through clean quartz sand the liquid 
which first passes through is almost free from the acid, and it is 
only when the sand has got a film of acetic acid on its surface 
that the mixture passes through unaltered. A similar action of 
quartz sand on a mixture of ethylic alcohol and fousel oil has also 
