478 Dr. Meyer Wilderman on the Velocity of 



is sure to be correct. We may safely regard as experimentally 

 verified and correct : (1) That every solid or liquid has a 

 vapour or solubility pressure. (2) That the laws of action 

 of mass are established for homogeneous systems. (3) That 

 the equation 



^=c(t -t)(t— * „ + K) 



regulates the velocity of reaction and equilibrium in case of 

 perfect equilibrium and the point of transition. 



If now we make an extended use of the very original and 

 happy idea of Van't Hoff of taking into account the fact that 

 solids or liquids have a vapour or solution pressure, we can 

 not only bring all three kinds of equilibrium and all kinds 

 of velocities of reaction in heterogeneous systems under one 

 general principle, but for the first time we arrive at the true 

 meaning of chemical equilibrium in heterogeneous systems. 

 and we are at last able to derive the equations for the velocity 

 of chemical reactions in heterogeneous systems, which experi- 

 ments have always failed to elucidate owing to the fact that 

 the phenomena in question are much more complicated than 

 was usually assumed. 



Let us first write down every chemical reaction and every 

 kind of chemical equilibrium in heterogeneous systems in a. 

 scheme. Care should be taken that this is done in a most 

 detailed manner, and that to every part of the scheme the 

 proper attention should be given. Let us start, say, with the 

 case of decomposition of solid NH 4 C1 into gaseous NH and 

 HC1: 



NH 4 C1 gas^NH 3 gas + HC1 gas. 



NH 4 C1 solid. 



An analogous case to this will be 



nAj in solution ^ mB, in sol. + m'Cx in sol. 



H . 



Aj solid (or liquid). 



We have to consider this kind of scheme not only in case 

 of equilibrium, but also in case of velocities of reaction. 

 Moreover it is of real importance and use, chiefly for the 

 latter : because in case of equilibrium we are always entitled 

 to consider that the solid NH 4 C1, which is in equilibrium 

 with gaseous NH 4 C1, is at the same time in equilibrium 

 with NH 3 and HC1 as well ; this, properly speaking, is 

 implied by the notion of the equilibrium of a system, but 

 we cannot make the same assumption for the velocity 



