324 
Proceedings of Royal Society of Edinburgh. [sess. 
molecules per unit bulk would be tlie same on the two sides of 
the membrane. If, for example, there are 1000 S molecules to 
one D molecule in the space A, the pressure on the piston P would 
be 1001 times the osmotic pressure, and on Q 1000 times the 
the membrane, we may annul the pressure on Q and reduce the 
pressure on P to equality with the osmotic pressure, by placing 
the apparatus under the receiver of an air-pump, or by pulling Q 
outwards with a force equal and opposite to the atmospheric 
pressure on it. When we do this, the annulment of the integral 
pressure of the liquid on the piston Q is effected through balancing 
by attraction, of pressure due to impacts, between the molecules 
of the liquid S and the molecules of the solid piston Q. We are 
left absolutely without theoretical guide as to the resultant force 
osmotic pressure. Put if the fluid be “liquid” on both sides of 
