IN LIVING MATTER 29 



proportions for combining, that 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 proportion 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 con- 

 centration 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 

 proved experimentally for the reaction between gaseous hydrogen and 

 bromine vapour. Here a mol ecule of hydrogen and a molecule of bromine 

 unite to form two molecules of hydrogen bromide, and there is no 

 change in number of reacting molecules ; thus H 2 + Br 2 = HBr + HBr, 

 accordingly we have P (H) or Br) K . P HBr , and no matter how the 

 pressure of hydrogen, bromine, and gaseous hydrobromic acid are 

 altered, the percentage of the three reacting constituents ought to 

 have the same ratio ; that is, there ought always to be the same per- 

 centage of bromine vapour converted into hydrobromic acid. This is 

 found to hold experimentally ; within fairly wide limits, no matter 

 how the pressure is varied, the percentage of conversion remains 



the same. 







III. Where a single compound splits up into two compounds, 

 or vice versd when the reaction is proceeding in the opposite direc- 

 tion. Under this class are also included those reactions in which, 

 although there are two substances on each side of the reaction, 

 one by passing out of solution or by blending with the solvent 

 with which it happens to be identical, develops no change m 

 osmotic pressure, and hence there is no work done on or by it, 

 and it does not come into the reaction. Such a reaction would 

 be included, for example, as a disaccharide splitting into its con- 

 stituent hexoses or vice versd, although the molecule of water 

 added to or taken away from the disaccharides in the reaction 

 makes the number of molecules apparently equal on the two sides 

 of the equation. The molecule of water in the reaction, however, 

 comes from or is returned to the great mass of water forming the 



