MICROPORES AND INTERFACES 55 



(4) The minute nature of the qiicuitities of solute zvhich mui/ be 

 removed from solution. A 100 c.c. of a 1 in 10,000 solution of 

 crystal N'iolet or eosin is completely decolorised by 1 gram of char- 

 coal in less than 2 minutes. 



The biological significance of adsorptions will be considered in 

 later chapters. 



D. Suspensions. — When very tiny particles of insoluble matter, 

 e.g., gold, carbon, etc., are dispersed through water, a large increase 

 of surface is produced and the physical properties of the liquid 

 become so remarkable that a separate branch of science with a 

 technique of its own has been evolved to study them. They will 

 be dealt with in a subsequent chapter. 



A special case of the multiplication of surface may be considered 

 now. A piece of charcoal has not only an external surface, but its 

 interior is ramified by a series of larger channels or macropores 

 (mean diameter 12|U,) and tiny capillary bores or micropores (mean 

 diameter 10 /x/x). When gas-free charcoal is immersed in water it 

 soaks up the fluid like a sponge, but takes in more water than its 

 volume would appear to justify. That is, some of the imbibed 

 water is compressed. This compression occurs in the micropores 

 with, of course, the evolution of heat. The net heat of adsorption 

 is closely proportional to the heat of compression under high 

 pressures. One gram of charcoal (not evacuated) immersed in 

 water gives off something like 18-5 gram cals. The molecules of 

 water in the micropores are arranged in parallel rows, closely 

 packed together, and so occupy less volume than either the 

 molecules in the macropores or in bulk. 



Tissues abound in potential micropores and in interfaces, and, 

 therefore, we w^ould expect that surface forces would play an 

 important part (a) in the structure of living matter, and (6) in 

 maintaining a balance between free and potential energy. 



Further Reading 



Willows and Hatschek. " Surface Tension and Surface Energy." J. and A. 

 Churchill. 



