KAHLENBERG — ACTION OF SOLUTIONS ON TASTE. 25 



the limit of taste of sodium nitrate solutions as given above 

 approximately, it follows that at the dilutions just mentioned 

 the taste of silver nitrate solutions is simply that of the silver 

 ions. Silver ions have a peculiar puckering effect on the mem- 

 branes of the mouth which, if the impression has not been too 

 weak, will remain for some time. The taste is frequently spoken 

 of as "metallic." At first it would seem that silver ions can be 

 tasted in more dilute solutions than hvdrogen ions: this is true 

 when we compare chemically equivalent quantities, but since 

 the atomic weight of silver is about 108, a ^ solution of silver 

 nitrate contains 1 gram of silver ions in 46300cc, while an ^5- 

 solution of hydrochloric acid contains 1 gram of hydrogen ions 

 in S00000 cc. 



Solutions of mercuric chloride can be very faintly tasted 

 when j^,, plainly when jfo. the "metallic" taste being some- 

 what similar to that produced by silver ions. Mercuric chloride is 

 not highly dissociated in solutions that are not very dilute. The 

 concentrations just mentioned are such, however, that in them 

 .the salt is lare-elv electrolvticallv dissociated. As CI ions can 

 not be tasted in ^ solutions, it is clear that we get here the taste 

 of the mercury ions. 1 



The Relations of Overton's Work to the Taste of Solutions. 



Ernst Overton in an interesting article, "Liber die osmotischen 

 Eigenschaften der Zelle in ihrer Bedeutung fur die Toxikologie 

 und Pharmakologie mit besonderer Berlicksichtigung der Am- 

 moniake und Alkaloide" (Zeitschr. f. physik. Chem. 22, p. 189, 

 1897), gives a list of organic groups arranged according to the 

 •degree of retardation that they exert in preventing the sub- 

 stance in which they occur from passing through vegetable and 

 animal membranes. The list beginning with the group that re- 

 tards most is as follows: 



1. The amido-acid group. 



2. The carboxyl group. 



1 Compare the work of H. Dreser, Zur Pharmakologie des Queeksilbers, Ref. 

 Zeitschr. f. physik. Chem. 13, 37, 1894. 



