22 THE THEORY OP IONS 



The taste or flavour of substances is due to the 

 reaction which is produced by a solution of that 

 substance upon the nerve-endings ; and the sense 

 of taste is regarded by some authorities as being 

 due to the dissociation which takes place in the 

 solution, that is, to the action of ions upon the 

 surface of the tongue or the nerve-endings. Eichards* 

 attributes the sour taste of acids to the action of 

 H ions in the solution ; which view he considers 

 upheld by the fact that a solution of HC1 of dis- 

 tinctly acid taste becomes tasteless when neutralised 

 by potash. Dilutions of less ionised acids, e.g. 

 acetic and tartaric, are not so sour to the taste as 

 corresponding solutions of mineral acids. When a 

 small quantity of sodium acetate is added to a dilute 

 solution of HC1 or acetic acid the sour taste is 

 diminished, which is in accordance with the view 

 that almost wholly dissociated sodium acetate is 

 capable of destroying the freedom of H ions. 

 Kalenberg,t on the other hand, says that the sour 

 taste of acids and acid sodium salts is obtained at 

 concentrations of H ions below the limit for acids ; 

 hence the sour taste of acid sodium salts cannot be 

 attributed to the H ions which are present, but 

 rather that it is due to the acid ion ; and he considers 

 this to militate against the view which explains 

 the sense' of taste by the theory of ions. Hober and 

 Kiessonf" also appear to consider the dissociation 

 theory to afford an unsatisfactory explanation of 

 the sense of taste. Richards, however, says that 



* Amer. Jour. Chem., 1898, xx., 121-126. 

 t Jour. Physiol. Chem., 1900, iv., 33-37. 

 J Abstracts, Jour. Chem. Soc., 1899, i., 206. 

 Jour. Physiol. Chem., 1900, iv., 207-211. 



