CHEMICAL AFFINITY. 425 



by the various methods show excellent agreement with 

 each other. 



A method which has been found well suited for the 

 comparison of the stronger acids with one another is found 

 in estimating the rate at which they accelerate chemical 

 processes. For example, cane-sugar solution will remain at 

 the ordinary temperature for an indefinite period without 

 showing any tendency to pass into a mixture of dextrose 

 and laevulose, but if an acid be present the inversion of the 

 sugar begins immediately, and goes on until the cane sugar 

 is completely transformed. It was found that the rate of 

 inversion with a given acid is very nearly proportional to 

 the concentration of the acid used ; but that for equivalent 

 quantities of different acids, the rate varies greatly. If the 

 acids are arranged in the order in which they accelerate the 

 inversion of cane sugar, it is found that this order is 

 identical with that obtained when the acids are arranged 

 according to their "avidities" as determined by an 

 equilibrium method. Other acceleration processes have 

 now been studied, and all agree in giving the acids in the 

 same order as they appear in the inversion of cane sugar, 

 which order is identical with that obtained when the acids 

 are arranged according to the electrical conductivity of 

 their equivalent aqueous solutions. There is no obvious 

 connection between these two properties of acids, viz., their 

 chemical reactivity, and their power to conduct electricity, 

 but an explanation is found in the electrolytic dissociation 

 theory of Arrhenius. His theory refers both properties to 

 the same cause — to the amount of dissociation of the acids 

 into the positive ion hydrogen, and the negative ion of the 

 acid. Acids are chemically active in the measure that they 

 produce hydrogen ions, which alone determine the specific 

 acid character. These hydrogen ions are also the chief 

 carriers of electricity in an acid solution, so that the more of 

 them an acid can produce when dissolved in a certain 

 quantity of water, the more active will it be chemically and 

 the better will it conduct electricity. The degree of 

 dissociation then of an acid is an excellent measure of its 

 strength. By applying the law of gaseous dissociation to 



