58 Dr. Meyer Wilderman on the Velocity of 



t — t y and to the surface of contact of these parts 2 ; C is a 

 specific constant, 



An analogous law no doubt exists for the velocity with 

 ivhich mechanical equilibrium is established in a homogeneous 



or heterogeneous system -J- =C / S(p — p). Provided no other 



phenomena interfere *, it will he directly proportional to the 

 difference of pressure in the different parts of the homogeneous 

 system, and directly proportional to the difference of pressure 

 and to the surface of contact of the different parts of the 

 heterogeneous system, ichen an equalization of pressure takes 

 place between them-, C is a specific constant. 



Passing now to the velocity of chemical reaction, we find 

 that this region is exceedingly complicated and, experi- 

 mentally, very difficult. It is enough to mention that alter 

 a period of about 40 or 50 years of research we have been 

 successful only in the determination of the laws concerning 

 the velocity of reaction in homogeneous systems (as far as 

 gases or solutions are concerned), but our attempts to obtain 

 a knowledge of the velocity of reaction in heterogeneous 

 systems, one may well say, remained theoretically and ex- 

 ] >eri men tally unsuccessful. 



The object of this paper is to furnish a solution of this 

 problem, guided and helped in the first instance by carefully 

 executed experiments. 



Before passing to the subject of this paper a few words 

 should be added concerning Gibbs's rule of phases, as the 

 present work has much to do with it, and this will introduce 

 order in the different subjects dealt with here. 



Gribbs's rule of phases is given in the Transactions of the 

 Connecticut Academy, 1874-78, pp. 152-156 . The quint- 

 essence of the rule can be formulated thus : — 



(i.) If the system consists of n kinds of molecules, and the 

 number of parts or phases in the heterogeneous system 

 r = n + 2 (experience shows that r can never be greater than 

 n + 2), no variation is possible in the parts of the system 

 which are capable of coexisting, because the concentration of 

 each kind of the molecules, as well as temperature and 



* Prof. FitzGerald was kind enough to draw my attention to the fact 



that the equation f- = C'(p —p) well expresses the law of equalization of 



pressure only when the resistances to motion due to viscous causes are so 

 great that the inertia of the masses set in motion can "be neglected 

 owing to the small velocities generated ; for example, owing to inertia a 

 body may move against the pressure, as in the case of air in a tube 

 expanding and rarefying itself to a lower pressure than the external 

 atmosphere. 



