460 Dr. M. Wildermann on Real and Apparent 



" Thus, dt = K (T — t) dz. We need not consider the signifi- 

 cance of K further ; it is sufficient to state that K is directly 

 proportional to the total surface of the solid solvend, and to 

 latent ' heat of fusion'." 



He further proceeds to apply Newton's equation 



dt=K'(t — t)dz 



to the cooling of a solution when no ice has been separated, 

 depending upon the convergence-temperature of the given 

 experimental conditions, and comes to the conclusion that the 

 real change of temperature is expressed by the superposition 



of the two equations, i. e. — =K(T o — t) +~K!(t — t); the 



dz 



thermometer-thread comes to rest when 



|=K(T o -O + K'(* o -*')=0, 

 and therefore ,/_t ^' (*' \ 



i. e. the temperature of rest of the mercury-thread is not at 

 T o (the real freezing-temperature), but at the more or less 

 different one t' which he calls the apparent freezing-tem- 

 perature. 



Prof. Nernst further thinks that as t — t' is positive when 

 t > t r , and negative when t < t', therefore the above equation 

 is to be applied equally for the case when the convergence- 

 temperature is above as when it is below the freezing- 

 temperature ; i. e. that, under all conditions, the deviations are 

 to be explained from the process of ice-melting ; an assump- 

 tion with which I cannot quite agree. 



Boguski investigated the action of acids on metals ; the 

 processes and equilibrium being purely chemical they have 

 little to do with the phenomenon of ice-melting and "perfect" 

 equilibrium. In the following considerations 1 start instead 

 from the idea of perfect equilibrium, and draw the conclusions 

 for the freezing-point method which necesarily follow from 

 the chief properties of this equilibrium. 



As known, the equilibrium between ice and water or ice 

 and a solution is a " perfect " one ; and this kind of equili- 

 brium is characterized by this fact, that at the smallest change 

 of its temperature (the freezing-temperature) one of the two 

 parts of the heterogeneous system must disappear. Above 

 the freezing-temperature the solid part (the ice), not the 

 liquid, disappears ; and below the freezing-temperature the 

 liquid, not the solid: therefore, if the convergence-temperature 

 be above the freezing- temperature of a given liquid, the hete- 



