474 Dr. Meyer Wilderman on the Velocity of 



taking place when the velocities of the two opposite reactions 

 become equal. Thus we apparently arrive in this case at the 

 same general statement made before in modifying the gener- 

 alizations concerning the velocity of chemical reaction and 

 chemical equilibrium in heterogeneous systems by the intro- 

 duction of the surface of contact St into the equations. 

 Such decomposition of the equation 



^= c (t -t)(t-t ov +K) 



cannot, however, be regarded as satisfactory, if the intrinsic 

 meaning of this decomposition cannot give us satisfaction and 

 cannot be generally adopted in all cases. Let us see what 

 this decomposition of the general equation means ? It means 

 that above as well as below the point of equilibrium the same 

 two reactions (solution of the solid and separation of the 

 solid) take place. Below the point of equilibrium the velocity 

 of separation of the solid is preponderating over the velocity 

 of solution of the solid, and above the point of equilibrium 

 the velocity of the solution of the solid is greater than the 

 velocity of separation of the solid. The velocity constant of 

 the solution of the solid is further assumed to be at the same 

 time, at any temperature, equal to the velocity-constant of 

 separation of the solid, be this temperature above or below 

 the point of equilibrium. It further assumes that at equili- 

 brium both reactions (separation and solution, condensation 

 or evaporation, &c.) continue, only both opposite velocities of 

 reaction become equal to one another, so that just as much of 

 each substance is formed in the unit of time as disappears. 

 To start with, we have no right whatever to assume that given 

 the same surface of contact of the reacting parts, the velocity- 

 constant of separation of salt or of ice from a supersaturated 

 solution or from overcooled water is equal to the velocity- 

 constant of solution of salt or of melting of ice in an 

 unsaturated solution, or in water above 0°. There is no evidence 

 for such an assumption; if anything, there is evidence 

 to the contrary. If an ice-crystal is brought into super- 

 cooled water, ice separates with a certain speed and we get a 

 velocity-constant. Now introduce, by means of a pipette, 

 some warm water to the bottom layers of the solution, stir 

 rapidly, and use the same separated ice for the melting process, 

 and the velocity-constant of melting is not found to be the 

 same. The difference is too great to be attributed to experi- 

 mental errors. It takes further a very few minutes to 

 separate the salt from a supersaturated solution, and you may 

 take even 10 or 100 times as much salt (powdered) and bring 



