68 Dr. Meyer Wilderman on the Velocity of 



experiments) they do not assume the temperature of the liquid 

 during the reaction simultaneously, and since their heat 

 capacity is in comparison with that of the liquid by no means 

 a negligible quantity, this constitutes a source of error. So 

 also is it with the reading of time. It is very difficult to 

 make accurately several readings during a time of 15 seconds, 

 if no special arrangements are made for the purpose. 



Now if the equation for the velocity of reaction is to claim 

 that it represents a law of nature it must satisfy two very 

 essential points : first, it must hold good for the whole curve,, 

 and, secondly, it must be general, and it must be based on a 

 simple clearly conceivable rational basis. It must be further 

 remarked that it is just the end of the curve which has great 

 theoretical interest, since the physico-mathematical theory of 

 freezing-points, vapour-pressures, solubility, &c. is very deeply 

 connected with this part of the curve. It was, therefore, of 

 importance to ascertain beyond any doubt whether the equa- 

 tions which I used in the theory of freezing-points (see " On 

 Real and Apparent Freezing-points and the Freezing-point 

 Methods,'" Phil. Mag. Dec. 1897 and Zeitschrift fur pltysika- 

 lische Chemie, 1899, p. 577) are correct, and if so whether, 

 in the case of all other kinds of perfect equilibrium, we also- 

 have to distinguish between " apparent " and " real " points 

 of equilibrium. 



The splendid arrangements of the Davy-Faraday Labora- 

 tory and the kind assistance given to me by Dr. Ludwig 

 Mond in procuring for me all the expensive instruments 

 necessary for this investigation, enabled me to resume the 

 same research in January 1896, under very much more 

 favourable experimental conditions of which a detailed account 

 is now given. 



The method employed is first described fully, as upon this- 

 the value of the whole research greatly depends. 



III. The Method of investigating the Velocities of the Separation 

 of Ice from Water and Solutions cooled helow their freezing 

 temperature, of the Separation of Salts from Super- 

 saturated Solutions, and of the Melting of Ice in Water and 

 Aqueous Solutions, Sfc. 



All the above reactions take place with very great speed,, 

 most of them lasting only a fraction of a minute, and as many 

 observations have to be made during this time in order to get 

 the curve for the velocity of reaction, the method described 

 below is the only one which enables us to investigate the 

 problem successfully. Advantage has been taken of the fact 



