970 Proceedings of the Poyal Society 
There are then two points for investigation. In the first case, 
can we find in sapid substances having, say a sweet or a sour taste, 
compound radicals always present, and from whose presence we 
may say that the taste-sensations result? Just, in fact, as the 
chemist associates certain properties with the presence of a certain 
radical in a substance, can we find similar associations with taste 
sensation ? 
In the second place, do we find that a compound radical, in the 
various combinations which it may form, preserves the character of 
its vibration, as shown by the spectroscope, unaltered in any marked 
degree ? 
The answer to the first question can be readily given, for it will 
be sufficient to obtain a list of substances giving a definite taste, and 
to search for some common or similar radical. If a radical common 
to all be found, we may safely answer it in the affirmative. 
There are among the carbon compounds many substances having 
an acid taste ; here is a list of the most familiar ones : — 
Acetic acid, 
CH 3 . CO . OH. 
CO . OH. 
Oxalic acid, 
1 
CO . OH 
CH 2 . CO. OH. 
Succinic acid, . 
■ • 1 
CH 2 CO . OH . 
yOH. 
Glycolic acid, 
. . ch/ 
N CO. OH. 
CO . OH 
Glyceric acid, 
j 
CHOH 
1 
CH 2 OH 
yOH. 
Lactic acid, 
CH 3 . CH< 
x CO . OH 
CH(OH) . CO . OH . 
Tartaric acid, . 
• • 1 
CH(OH) . CO . OH . 
Benzoic acid, . 
C 6 H 5 .CO.OH. 
