361 



as equal to the values given by the sodium salt of an analogically 

 built acid in the same dilution. As the properties of the acid salts 

 of the «-sulphoncarbonic acids indicate the structure CHR (COJijSOjNa, 

 the sodium salt of a sulphonic acid may be chosen for the sake of 

 comparison. 



Now, with a view to determine the dissociation degree of a 

 monobasic sulphonic acid, related to the acids in question, the anilide 

 of sulfonpropionic acid was prepared ^). The conductivity mentioned 

 in the table shows that this propionanilide-^<-sulphonic acid is a strong 

 acid, from which it follows with certainty, that the sulphonic acid 

 group is free and that the carboxylic group is changed into amide: 

 CH, .CH(C0NHC,HJ.S0,H. 



If [X(^ is assumed to be 368, a value resulting from the 

 conductivity of the sodium salts and also from the Jiumber of atoms, 

 then the mean dissociation constant for the dilutions 64, 128 and 

 256 is found to be 0,39. 



For the sodium salt, the conductivities at the dilutions 256, 512 

 and 1024, extrapolated according to Bredig, give (i^ = 79,0. 



From this results the ionisation degree a at the dilutions v : 



v=: 16 32 64 128 256 512 1024 



«=z 0,797 0,843 0,881 0,904 0,928 0,948 0,966 



These values are also taken for a,, the dissociation degree of 

 NaHA (reaction 1). 



The conductivity of the acid salt jLtNniiA, diminished by «^(^Na*+'^ ha), 

 will give, as a first approximation, the conductivity due to the ions 

 H* and A". 



In order to get a value for k^, il is necessary to know the con- 

 ductivity which the ions H' and A" would give at a complete 

 ionisation according to reaction II. 



The equivalent coiïductivity of the neutral sodium salts diminished 

 by ^Na*, gives Aa"» In this way the value 72 was found for sulphon- 

 acetic acid and 65 for sul phon propionic acid. 



The conductivity of the ions H' and A" at infinite dilution is 

 then expressed by ^h -|- 2Aa". 



The observed conductivity fiNatiA — «i(^Na* + ^ha' ). divided by 

 this value ^h* + 2Aa , gives, as a first approximation, the value 

 of a,, the dissociation degree of reaction II. 



1) Recueil d. tr. ch. 40, 585 (1921). -^ -0. ir.il 



