20 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
ADSORPTION. 
Both at all-liquid and solid-lquid interfaces concen- 
trations of previously-dissolved substances are well-known 
phenomena, and are then termed ‘ adsorptions,’? when it 
can be proved, or inferred on general grounds (such for 
example as their diminution by rise of temperature) that 
they are attended by diminuation of the surface-energy of 
the system. 
As it is by no means always easy to exclude the 
possibility that chemical combination of the adsorptum with 
the adsorbent, or solution in it, has occurred, it should 
be realised that the theoretically simplest cases of adsorption 
are those which occur at free surfaces— adsorption without 
adsorbent ’ as they might be described—and also that for the 
practical study of some aspects of adsorption these often 
offer very special advantages. 
It may be well to point out that the hsndiieee that 
flocculation of solid suspensions is proof that the part- 
tension of the water in contact with the suspended solid has 
imcreased from an initial negative, or at most feebly positive 
tension, into a stronger positive tension, 1s Im no way 
inconsistent with the view that the flocculation results from 
a true adsorption, and has therefore been attended by 
a decrease of the total surface energy of the system. Thus 
in the flocculation of kaolin in water which follows the 
addition of a small quantity of calcium chloride, this is 
presumably preceded by an adsorption of the lime salt (or 
one of its ions or hydrolytes) and attended by a fall in the 
total surface energy of the system. Since none of this fall 
could be attributed to diminution of contact between a 
soluble substance like calcium chloride and water, it must 
be due entirely to fall in the total tension of the kaolin- 
water interface. ‘To reconcile the conclusion that the rise 
