178 
b. the lowering of the surface-tension of water, which they bring 
about. 
In view of this supposition it avails to know the boiling point 
of the odorous substances as well as the number of droplets of the 
diluted aqueous solutions. The subjoined tables (Ila and 115) give 
us these data. They do not warrant the adoption of an immediate 
connection, though we may conclude from them that there is a 
more remote relation *). 
The sign of the charge may also be of some influence. Whereas 
for 24 out of 26 substances examined in widely different concen- 
trations, we invariably found a positive charge, which eventually 
disappears with progressing dilutions, a negative charge is yielded 
by caproic acid and valerianie acid in highly diluted solution 
(positive in somewhat concentrated solutions). In the extremest 
dilution, in which this negative charge is just noticeable, the smell- 
intensity of these substances, when compared with the average of 
our substances, appears to be very slight. 
Whether the charge increases or not, or whether it decreases, 
through tbe addition of some common salt to the solution °), does not 
seem to interfere with the relative arrangement of our 26 substances. 
With all of them we observe an increase of the electrifying power, 
with the exception of naphtalin, indol and skatol, whose insignificant 
charge seems to remain constant, and of artificial moschus, pseudo- 
cumol, p. xylenol and thymol, whose charges are obviously getting 
weaker. 
We conclude, therefore, merely from the facts, without attempting 
to find an explanation, that also of odorous substances, chosen at 
random, in approximately similar dilution, the smell-intensity and 
the electrifying power have reached their limen of perceptibility. 
1) Order of the number of droplets of the saturated solution: 
Naphthalin 49.3, Artificial moschus 49.6, Toluol 50.3, Pseudocumol 50.5, Benzol 
50.75, Allylalcohol (1: 500)51, Vanilline 51, Indol 51.5, Skatol 52.2, Xylol 55, 
Nitrobenzol 55.5, Pyridin (1/9) 57.25, Cumidin 66.75, p. Xylenol 68.5, Anilin 69, 
p. Toluidin 69, Thymol 73, o. Toluidin 75.5, n. Xylidin 77, m. Xylenol 84, 
Caproic acid 84.5, Guaiacol 85, Terpineol 90.5, Valerianic acid 106, Isoamylacetate 
115, Amylalcohol 131. 
4) E. L. Backman, Researches Physiol. Lab. Utrecht (5). Vol. 18, p. 349; 19, p. 210. 
