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trically charged metallie plates. To this end the full seent, furnished 
by an olfactometrie cylinder pushed off to its full length (Le. p. 65), 
was sent for five minutes through a nickel-plated tube 10 em. in 
length and 0,8 em. in bore, while the insulated tube was charged 
to 220 volts. The metallic tube consisted of two parts insulated from 
each other, which, therefore, could be charged oppositely. When 
the five minutes had elapsed we tried to find out if any odour 
adhered to the wall and how long it remained there. Such was the 
rapidity at which the air was drawn through the olfactometric 
cylinder and the nickel tube that as much as 6 Litres passed every 
minute. 
The determination of the odorimetric coefficients as well as the 
compensation- and combination-tests were performed with some of 
ZWAARDEMAKER’S precision-olfactometers. The rapidity of the airstream 
was the same (6 Litres per minute); besides the smelling took place 
after the air had been streaming for precisely */, minute. At that 
moment the connection with the suction-pump was broken, the 
communication with the olfactometrical cylinder was arrested, smelling 
took place through a short side-tube at the reservoir, the latter or 
a capacity of about 100 cc. Every experimental sitting comprised 
a number of tests of the same day together with those of previous 
days. Only the averages have been tabulated. The olfactometrical 
cylinders were invariably filled the previous day with a saturated 
aqueous solution of the terms of the homologous series. 
Liminal Stimuli of the methyl-benzol series. 
Benzol 5,0 10- Grams per Litre of air 
Toluol 2,0 10-6 rr a 4 BN 
Xylol iS. 57.1 Oet ARTE Pa ee 
Pseudoenmol 0,2 LO 5 a) yeas ct valet 
Durol OOS = 1057 fs A KS tte 
These values expressed in gram-molecules per Litre of air 
Benzol 6,50 10 gram-molecules per Litre of air 
Toluol 2,17 1059 x a Moe ae 
Xylol 0,76 10-3 ‘3 EON 
Pseudocumol 0,18 LOE op is pp ET 
Durol 0,07 105 Ps En rot a 2 
These determinations fully bear out Harcrart’s rule that in the 
homologous series of organic chemistry the smell-intensity at first 
gradually runs up as we pass from the lowest to the higher terms. 
By further addition of methyl-groups the amount of matter, required 
