14 BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



due to the hydrogen ions present. 1 In order to firmly establish 

 this experimentally a 355 hydrochloric acid solution was prepared ; 

 this I found to have a very decided acid taste. From this solu- 

 tion 335, j&j and 555 solutions were prepared as before described. 

 On testing the fifteen individuals mentioned, it was found that 

 four of them could detect a difference between the ^ solution 

 and the distilled water, while all of them distinctly tasted the $& 

 solution. The ^ solution was reported not as sour, but as 

 slightly astringent ; the ~ was reported as astringent by the men 

 but by the ladies uniformly as astringent and slightly sour. 2 As 

 at these dilutions the dissociation of the hydrochloric acid is 

 practically complete, and as it requires a much stronger solution 

 of Na CI than ^ to cause taste, as will be shown below, it 

 is clear that the sour taste is simply due to the effect of the hy- 

 drogen ions. I have no doubt that with cultivation of the taste 

 for hydrogen ions, and previous elevation of the temperature 

 of the solutions to that of the body, even more dilute solu- 

 tions than 555 could be detected by the sense of taste. Indeed, 

 the experiments of Richards 3 confirm this. He shows clearly 

 that fairly accurate titrations of hydrochloric acid can be made 

 using the taste of the solutions to indicate the end of the- reac- 

 tion. 



The 355 solution of hydrochloric acid was uniformly re- 

 ported as sour, as was of course also the Ufa. Solutions of sul- 

 furic, hydrobromic, and nitric acids equivalent to those of hy- 

 drochloric were also prepared, and the subjects were tested with 

 these. The results were the same as with the corresponding so- 

 lutions of hydrochloric acid. The Jk solutions were re- 

 ported as astringent by those that could distinguish them from 

 distilled water, ^ were reported as astringent by the men 



1 After the presentation of this paper to the Wisconsin Academy and before it 

 could be published, there appeared an interesting article by T. W. Richards on 

 "The Relation of the Taste of Acids to Their Degree of Dissociation," Amer. 

 Chem. Jour., Feb. 1898. He also expresses the idea that sour taste is caused by 

 hydrogen ions. 



2 0n the whole, I found but little difference in the delicacy of the taste of the 

 different persons tested; I had anticipated much greater individual differences 

 than I actually found. 



3 Loc. Cit. 



