488 Dr. Meyer Wilderman on the Velocity of 



are passing into the solution ; therefore : — 



eM P .- P r)=c' P ,. P ^, PT = v 0^^,. . (iii .) 



and * s;( Po -^f^W_/^\. (iii/> 



i. £., the velocity of solution of zinc or marble in acids, such 

 as HC1, HBr, NOJEt, must be a function of the surface of 

 the solid and of the square of the concentration of the acid. 

 The equation for the velocity of solution of marble or zinc in 

 acids belongs to the comparatively very simple cases, but is 

 nevertheless of quite a different form from that which De la 

 Eive or Boguski could, under their circumstances, suppose. 

 since the form and kind of the processes which come into con- 

 sideration, as well as the laws of evaporation, solution, &c, were 

 not known to them when they carried out their experiments. 



It must further be remarked that the equations ( — V ( — \ 

 J [ W \dr)' 



Sfc, must be taken as they actually are, with all the additional 

 terms for the deviations and abnormalities of whatever kind 

 they may be, should any such complicate or limit the 

 phenomena. For instance, the laws of action of mass are 

 applicable chiefly to diiute solutions or to gases in the dilute 

 state, they cease to hold good as we pass to greater concentra- 

 tions or to higher pressures. Often the products of the 

 reaction influence the velocity of the reaction and complicate 

 the phenomenon. Reactions of a higher order often occur as 

 if they were reactions of a lower order, &c. 



It may be well to emphasize again that the equations derived 

 here for the velocity of chemical reaction in heterogeneous 

 systems hold good only from the time when the velocities 

 become equal and they give no information as to the velocity 

 of reaction before this takes place. For this reason it may 

 happen, though under very exceptional conditions, that one 

 or more of the reactions in the system may first have to 

 almost complete themselves before they can become equal to 

 the rest of the reactions in the system, i. e., that so far as 

 these reactions of great speed are concerned only a small 

 region of their individual curves will be governed by the 

 above equations. 



III. On the real and apparent points of chemical equilibrium 

 in heterogeneous systems. 



It was shown before (Part II.) that all physical reactions 

 between the same substance in the different parts of the hetero- 

 geneous system never reach^ because of the nature of the 



