Reaction before Complete Equilibrium. 59* 



pressure, can have in every part of the system in this case 

 only one definite value. There is therefore only one point 

 ;it which equilibrium is possible (van't HofFs " point of 

 transition "). 



(ii.) If the number of parts or phases in the heterogeneous 

 system r=n + l, all variables up to one are determined ; to 

 each temperature corresponds also a definite pressure and 

 a definite concentration of each of the substances in the parts 

 of the system, i. e., we have not only one point of equilibrium 

 but a continuous series of them, a curve. This kind of 

 equilibrium is called " complete." 



(iii.) Lastly, if the number of phases r=n, at a given 

 temperature or pressure the values of the concentration of 

 each kind of molecules in the phases remain undetermined y 

 i. e. s each part or phase may contain different concentrations 

 of each kind of the molecules, and the system may remain in 

 equilibrium. This kind of equilibrium is called " incoi^lete." 



The object of the author's experimental investigations was 

 in the first instance to find the law concerning the velocity of 

 reaction in the system before " complete equilibrium " or its 

 "point of transition" is reached. For this systems were 

 investigated on the freezing-point and the solubility-curve, 

 where n = 2, r = n + l = 3, e.g., systems consisting of pure 

 solid solvent, solution and vapour, or system- consisting of 

 solid salt, the saturated aqueous solution and vapour. Again, 

 systems were investigated where n=l or 2 and r = n-\-2 

 i. e. = D or 4, e.g. systems consisting of ice, water, and vapour, 

 or consisting of ice, solid salt, saturated solution, and vapour. 



II. Velocity of Reaction before Complete Equilibrium and 

 the Point of Transition are reached. 



The velocity of reaction before complete equilibrium has 

 formed the subject of my investigation since 1895. In the 

 Zeitschrift fi'n- physikalische Chemie, January l<S9u", I pub- 

 lished a short communication on the velocity of separation of 

 ice from overcooled water and from aqueous solutions. I 

 have had, however, to repeat my experiments more carefully, 

 with a more sensitive thermometer. Herr Gotze, at Leipzig, 

 has constructed for me an exceedingly sensitive 1/100° mer- 

 cury-thermometer. The mercury-bulb of the thermometer 

 is very thin and long, and the glass wall of the bulb is as 

 thin as the skill of Herr Gotze allowed him to construct. 

 The time was read with accuracv to 1- second, and in this 

 Mr. Still, of Phrist Church, Oxford, assisted me. The 

 arrangements of the experiments were those which I used iu 



