944 
homologous series have been established (Haycrart'), J. Passy ®, 
ZWAARDEMAKER *), and quite recently the electrical phenomenon 
(ZWAARDEMAKER f)). . 
The present communication deals with the liminal stimuli of a 
series not yet investigated, the possibie combinations within the 
series, the diffusion-vate, the adsorption to electrically charged metal- 
lic plates and the intensity of the vapour-electricity of the terms. 
We generally made use of ZWAARDEMAKER’s experimental method °). 
The just noticeable smell was determined in the smell-chamber 
(Le. p. 56) by evaporating extremely small quantities of odorous 
matter in aqueous solution at a carefully maintained temperature 
in the space of 64 Litres. The determination did not take place 
before 3 or + minutes after complete volatilization. Between two 
determinations the chamber was aired and the adhering scent was 
removed from the, walls by means of chalk and a towel. In the 
same chamber, now provided with a back-wall of tilterpaper, im- 
pregnated with the saturated aqueous solution, we measured the 
diffusion. By repeated determinations we established the time required 
for a distinct sensation of smell in the centre of the opposite wall. 
For a quantitative determination of the vapour-electricity produced 
by spraying the several terms, we employed a glass sprayer and a 
circular aluminium plate 20 cm. in diameter, connected to an 
Exner-electroscope. The sprayer as well as the cap of the electro- 
scope were earthed, the aluminium plate, however, had been carefully 
insulated by mounting it on a block of paraffin. Invariably 10 c.c. 
were sprayed under an overpressure of two atmospheres through 
compressed air. By establishing the capacity of the electroscope with 
receiving plate and the magnitude of the deflections at successive 
voltages the number of coulombs, obtained per c.c. as a charge on 
the plate, could easily be ascertained. Under these experimental 
conditions no charge was obtained by spraying pure water. Before 
performing the measurements we first searched for the optimal 
distance between sprayer and aluminium dise at which we could be 
sure of the maximal charge. The tables show the averages of the 
charges in coulombs per c.c. of sprayed liquid, calculated from the 
deflections of the electroscope. 
The adsorption of the odorous substances was examined for elec- 
1) Haycrarv. Brain Il 1888 p. 166. 
2) J. Passy. Compt. rendus. Mai 1892, Mai 1893. 
3) ZWAARDEMAKER. Die Physiologie des Geruchs. Leipzig, 1894 p. 238. 
4) ZWAARDEMAKER. Proceedings Kon. Ak. v. Wetensch. May 27 1916. V ol. 25, p. 3. 
5) Cf. TigeRsTEDT’s Hdb. d. physiol. Methodik. Bd. 3 p. 46. 
