CHAPTER V 

 LIBERATION OF ENERGY 



(3) ENERGY OF SUBSTANCE IN SOLUTION 



" The problem of achieving perpetual motion contrary to the second law " (of 

 thermodynamics) " is that of bringinir order and direction once more into the chaotic 

 rush of the molecules, to marshal and drill the mob so that once more they can act 

 together to produce a common effect." Soddy, 



Osmotic Pressure. 



The first process that affects food is that of digestion. Digestion 

 is merely the breaking down of the material supplied so that 

 it can pass through the absorl)ing medium in solution. It follows 

 (from this statement and from the physical state of the living 

 cell) that all energy manifested by an animal ccmes from sub- 

 stances in solution. No material is of any use for energy purposes 

 unless it is soluble, and imtil it is rendered soluble it cannot be 

 absorbed and utilised. 



The mere solution of a substance may so alter the state of that 

 substance that energy is set free. (Cf. heat evolved on diluting 

 concentrated H2SO4.) When a solid goes into solution it at once 

 loses the properties characteristic of the solid state. Its particles 

 become mobile, and all the properties dependent on regular 

 molecular arrangement disappear. Thus the solid may be optically 

 active or doubly refracting, and the solution quite void of these 

 properties. The passage of the substance into solution bears some 

 resemblance to its passage into the liquid state. A doubly- 

 refracting crystal almost invariably loses its double refraction when 

 it melts ; and most substances which are optically active in the 

 solid state are inactive when fused. The substance might conceiv- 

 ably have passed into the gaseous state. Physical chemists are 

 agreed that this is the most probable course. They find that for 

 dUuic solutions, at any rate, the simple gas laws hold good. 



In order to explain and correlate these gas laws and the 

 phenomena of solution, evaporation, etc., the Kinetic Theory of the 

 structure of matter has been formulated. The views that have 

 been held regarding the constitution of solutions have been very 

 varied, and since Thermodynamics is too general in its method 

 of treatment to yield a complete answer to the problem, hypotheses, 



35 3—3 



