LIVING MATTER AND ITS PRODUCTS 153 



When a disaccharide is hydrolysed (for example, maltose into 

 two molecules of dextrose), as in the equation 



C 12 H 22 O n + H 2 <~> C 6 H 12 6 + C 6 H 12 6 , 



PI Sr 



the equation of equilibrium is, as deduced above, ^r P . e ' 



LA 



where P B is the osmotic pressure of the hexose at equilibrium, 



P 2 



and P^ that of the disaccharide; this may be written ^"^K, 



"A 



or PB=K P A . Expressed in words, there is a constant ratio 

 between the osmotic pressure of the disaccharide and the square 

 of the osmotic pressure of the hexose. As a result, the point of 

 equilibrium is not fixed and independent of the concentration of 

 the reacting substances as in the types of reaction previously 

 discussed, but varies with the initial concentration of the solution, 

 in such a way that in dilute solutions the equilibrium lies where 

 the whole of the disaccharide is dissociated into its constituent 

 hexoses, while as the solution becomes more concentrated the 

 equilibrium point lies more and more towards complete conversion 

 into disaccharide. This is obvious, for if the concentration of 

 disaccharide in the solution be doubled so that P A becomes 2P A , 

 then P B only becomes \/2 . P B that is, with increasing concentra- 

 tion P B increases in a less ratio than does P^ ; conversely on dilution, 

 P B decreases in a less ratio than P A , and hence in dilute solutions 

 P B increases relatively to P A . L 



In the case of a neutral fat or triglyceride hydrolysing in solu- 

 tion, 2 three molecules of fatty acid and one of glycerine are formed 

 from each molecule of the fat, and the equation of equilibrium 

 becomes P E 4 K . P A . Accordingly, the effect of concentration 



1 It may be pointed out that an electrolyte, such as sodium chloride in 

 aqueous solution, behaves similarly and for the same reason. In dilute 

 solution, the electrolyte is practically dissociated into its ions, while in con- 

 centrated solution an amount proportional to the osmotic pressures of the 

 different reacting substances is undissociated. The type of reaction is the 

 same as that discussed above. If at equilibrium, the osmotic pressure of 

 the undissociated molecules is represented by P s and that of each ion by 

 P T , then as above for equilibrium we have P s =K.P t 2 , and the same reasoning 

 as given above shows that Pj increases relatively to P s with increasing dilution. 



2 The neutral fats are practically insoluble in water, but the reasoning 

 holds for fats in solution in the cell protoplasm. 



