OF VITAL PHENOMENA 5 



near one end as to be ascertained with difficulty. The above 

 reactions were given as an example because their nature seems 

 to be better understood. The reactions whose rate can be easily 

 measured are usually splittings and combinations of molecules. 

 Many of these have been found to obey the laws of mass ac- 

 tion. A monomolecular reaction in unit volume is expressed: 

 dx 



— = c(a — x), where a is the original amount of substance, x is 

 dt 



the amount transformed in the time t, and c is the constant of 

 the reaction that it is desired to find. From the calculus we 



1 1 



obtain: c = — log e . In this equation log e signifies the 



t a — x 



natural logarithm (to the base e = 2.71828), but this may be 

 reduced to the common logarithm (to the base 10), abbreviated, 

 logio °r log- Since log 10 = log e X 4343, the above formula be- 

 1 1 



comes : c = — -4343 log 10 • When several kinds of mole- 



t a — x 



cules are concerned the formulae become much more complicated, 

 but in biochemistry we are less often concerned with the rate 

 of reaction than with the point of equilibrium of a reversible 

 reaction. 



This equilibrium point in a reversible reaction is illustrated 

 in the case of H 2 0. The H 2 dissociates into H : and OH' 

 and these recombine to form H 2 0. This is in one direction a 

 bimolecular (bi-ionic) reaction, and in the reverse direction a 

 monomolecular reaction. But this latter, the dissociation of 

 H 2 0, may be disregarded mathematically because the concentra- 

 tion of the' H 2 (at constant temperature) does not measurably 

 change. At the equilibrium point [H*]X{OH'] = a constant, 

 where [] denotes the concentration of what follows. At 22°, 

 [H*]X[OH'] = io~ 14 and therefore if we increase the concen- 

 tration of H by adding acid the concentration of OH' is de- 

 creased, and vice versa. In pure water [H*] or [OH'] = icr 7 

 at 22 and any variation from this is acid or alkaline. We may 

 measure acidity or alkalinity either by estimating the concentra- 

 tion of the H or OH', but the hydrogen ions are the ones usually 

 estimated, as will be described in a succeeding chapter. 



In any neutral dilute aqueous solution the concentration of the 



