lfc» BULLETIN OF THE UNIVERSITY OP WISCONSIN. 



interesting question of the taste of acid sodium salts of polybasic 

 acids is contemplated. 



The foregoing results and those of Richards show conclusively 

 that hydrogen ions have a sour taste ; furthermore, it is clear that 

 in very dilute solutions they produce simply an astringent sen- 

 sation. The question arises, Is sour taste always due to the 

 presence of hydrogen ions? I am inclined to answer this ques- 

 tion in the affirmative, for I know of no substance that has a 

 sour taste which on going into solution in water does not yield 

 hydrogen ions. 



With regard to the astringent effects, it seems that in many 

 if not in all cases these can he ascribed to the presence of 

 hydrogen ions in about ^ solution. I was deeply impressed 

 with the fact that many of the subjects tested said that the 

 jJe solutions of the mineral acids tasted like alum. It has 

 been shown 1 that alum solutions contain hvdrogen ions in small 

 quantities due to the so-called hydrolytic dissociation of the 

 aluminum sulfate, i. e., to a reaction of this salt with water 

 forming a small amount of sulfuric acid from which in turn 

 by electrolytic dissociation hydrogen ions form. In presence 

 of the sulfate of the alkali metal an acid salt would no doubt 

 form from which, according to previous investigations, 2 hydro- 

 gen ions split off rather difficultly. The acid reaction of alum 

 solutions toward indicators is of course further proof of the pres- 

 ence of hydrogen ions. The astringent taste of solutions of fer- 

 ric salts and their acid reaction toward indicators are well 

 known; these solutions like those of aluminum salts have long 

 been used in medicine because of their astringent properties, 

 which I am inclined to ascribe to the hydrogen ions present due 

 to hydrolytic dissociation. This statement is of course not to be 

 construed as meaning that the other ions and the undissociated 

 molecules present in these solutions do not exert an effect, for 



1 See Long's work on the inversion of sugar by salts, Jour. Amer. Chem. Soc. 

 18, Feb. and Aug., 1896. 



2 See Trevor, Zeitschr. f. physik. Chem. 10, p. 321; Tower, ibid. 18, p. 17 u. 21, 

 p. 90; Smith, ibid. 25, p. 144. 



