by the following equations : 
— de 
— af Te k, 1e, Seri Ven Hea 
dt 
and 
de 
Ml == Kae Ue, == i He, 
dt je 7 
in which the change in concentration of the intermediate product 
is indicated by: 
deg de, de 
en ke, He, — ka, He, — ha, Hea + k, Mer. 
dt dt dt 
So in general the velocity will not be represented by the simple 
expression of the law of mass-action *); this is the case only when 
ka, and ka, are both very great with respect to 4, and &,, in other 
words when no appreciable quantities of the intermediate products 
occur in the reaction mixture *). 
An example of this furnishes the reaction Ni + 4CO = Ni(CO),, 
in which the measurements of the velocity show that the reaction 
takes place from the left to the right over Ni(CO),, which, however 
is so quickly decomposed, and combines so rapidly with an excess 
of CO (kg, and ka, great), that it cannot be demonstrated in the 
reaction mixture. 
But there is little reason to assume that every reaction should be 
thought to be such that the reacting substances break up into pieces 
(either atoms or groups of atoms), which unite again as free compo- 
nents in another way; on the contrary room should be left for the 
possibility that throughout the reaction no other independently moving 
particles occur than the molecules of the initial and the final products. 
This supposition is undoubtedly greatly supported by the fact that 
substances which are in themselves exceedingly stable, and do not 
present the slightest trace of dissociation in pure condition at a 
definite temperature, are yet liable to be analysed by means of an 
added substance. If to take a conerete example, we consider the 
reaction : 
H, + Cl, = 2HCI 
1) That in this case the reaction neat must be split up into two parts one of 
which is the heat of reaction of the decomposing substances in the intermediate product, 
the other that of the forming substances into the intermediate body, seems to us 
not doubtful; this refers, however, to the splitting up of a constant of equilibrium 
into two other constants of equilibrium, each of which must then again be split 
up into two constants of velocity. 
*) Zie SCHREINEMAKERS Chem, Weekblad 1. 625 (1904). 
