LIVING MATTER AND ITS PRODUCTS 151 



If the chemical energy of transference from substance A to sub- 

 stance B is zero, the constant becomes unity and the equation 

 is P B =P A . This condition is probably attained with stereo-isomers, 

 and hence when the two isomers are formed in any reaction they 

 are turned out in the condition of equilibrium that is, in equal 

 quantities and we get, as in the case of the synthetically prepared 

 sugars, the indifferent compound consisting of an equimolecular 

 mixture of the two isomeric bodies. 



II. Where two substances, A and B, interact to form two 

 others, C and D : 



|^ = e^ T = K, or P C .P D = KP A .P B 



* A -^ B 



that is, the product of the osmotic pressures of the one pair of 

 substances is proportional to the product of the osmotic pressures 

 of the other pair of substances. 



If the substances A and B at the commencement are in equi- 

 molecular concentration, then P A =B B , and since the substances 

 C and D are then also formed in equimolecular concentration also 

 P =P D , and hence the equation for equilibrium can obviously 

 be simplified to P (c or D) =K . P (A or B) . That is, the osmotic 

 pressure of the substances formed always bears the same ratio to 

 the osmotic pressure of the substances from which they are formed 

 when the equilibrium point is reached. 



It follows that for reactions of the type I., and for those of 

 II. when the substances are present in the proper equimolecular 

 proportions for combining, the equilibrium point is not affected 

 by the concentration of the solution. That is, whether the reaction 

 occurs in very dilute or in concentrated solution (within the limits 

 at which the gas laws hold for osmotic pressures), the same pro- 

 portion of A is turned into B in type I., and of A and B into C 

 and D in type II. This is obvious, for if P A =K P c , then if P A is 

 doubled, so must P c be in order that the equation may still hold, 

 or, in other words, no matter what is the original concentration 

 of the reacting substances, the same percentage is always turned 

 into the substances formed before equilibrium is reached. 



The law that the equilibrium point is fixed where the reaction is of 

 the types I. or II., and is independent of the concentration, has been 



