248 liEPOkT— 1901. 



From this we get 



Fhci-/'i 



From this the degree of hydrolysis can be calculated. 



The conductivity of the hydrolysed salt M can be directly measured 

 with a certain amount of 'accuracy. The experimental error will amount 

 to perhaps O'O per cent, under favourable circumstances, rising to 1 per 

 cent, or more at tlie highest dilutions (about i^/fnr normal). 



Similarly //hoi can be ascertained by direct measurement. 



The problem is, therefore, to ascertain what the molecular conductivity 

 would be if the salt were not hydrolysed, that is, //,. There are several 

 ways of arriving at this, but none permitting of any great accuracy. 

 Walker was the first to attempt to measure hydrolytic dissociation in this 

 way.^ He determined the electric conductivities of the chlorides and 

 sulphates of a number of very weak organic bases, including salts which 

 were hydrolysed to the extent of nearly 100 per cent. 



He arrived at the approximate conductivity which the salts would 

 have in the unhydrolysed state by analogy with similar salts which were 

 known not to be much hydrolysed, and assumed that the molecular 

 conductivities would be equal at the same dilution. As the degrees of 

 hydrolysis were in all cases very large, this served his purpose tolerably 

 well. For instance, for thiazolhydrochloride in --}^ normal solution he 

 found M= ISO'S. He assumed the real value yu, to be 90. /(hci was known 

 to be 375. 



189-8-90 „ „^ 

 Hence x= r,^- — n7T~=0'3o, 



i.e., the salt is hydrolysed to the extent of 35 per cent. From the 

 catalysis of methylacetate he found 34-6 per cent. The values that he 

 found in this way corresponded pretty closeJy with those obtained by 

 catalytic methods. 



This method of analogy gives, however, only a very rough approxi- 

 mation of the conductivity of the unsplit salt. It was probably several 

 units out in most cases, and for this reason tlie method is not adapted to 

 the determination of small degrees of hydrolysis. Errors of several per 

 cent, are unavoidable. In the case of the less hydrolysed salts no results 

 could be obtained at all. Indeed, in the case of aniline hydrochloride he 

 found the conductivity to be considerably smafler than that calculated 

 from the velocities of migration of the ions which it contains. It is there- 

 fore evident that some more satisfactory method is necessary for the 

 determination of the true conductivity (m,) of the salt in absence of 

 hydrolysi-s, if small percentages of hydrolysis are to be measured. 



Bredig ^ extended Walker's work in this direction. He determined 

 the true conductivities of such salts as aniline hydrochloride by a very 

 simple device. He added aniline to the solution, and in this way drove 

 back the hydrolysis to such an extent that he could arrive at the true 

 conductivity of the salt. In this way he determined the hydrolysis of 

 aniline hydrochloride and a number of its derivatives. 



The converse method of reducing the hydrolysis to a minimum by 



' Zeitschr.fiirphijs. Cliem.,^, 333 (1889). 

 * Jbid. 13,321 (1894). 



