946 
to produce a just noticeable smell-sensation, gradually diminishes. 
The increment of smell-intensity is even approximately proportional 
to the number of methyl-groups. The smell-intensity of toluol is 
about three times greater than that of benzol, that of xylol about 
three times greater than that of toluol and that of pseudocumol 
about four times greater than that of xylol. The smell-intensity of 
Durol is only about twice that of Pseudocumol: the increment of 
intensity therefore, is smaller than might be expected from the 
ratios found previously. Most likely this is why on further methylation 
ihere is an absolute decrease of smell-intensity. 
Dijfusion-rate over a distance of 40 cm. at 19° C. 
The time required for a perceptible smell-sensation set up by the 
terms of the series at a distance of 40 em. is: 
Benzol 1 min. 15 see. 
Toluol {Sle gs — ABB es 
Xylol 00s; 
Pseudocumol G0 a5, 
Needless to say that, in order to determine the precise diffusion- 
rate also the tension of saturated vapour and the smell-intensity has 
to be taken into account. 
Electrical charge by spraying. 
First of all the charge of sprayed saturated solutions was 
determined. True, such solutions do not admit of easy comparison, 
the solubility in water of the members of the methyl-benzol series 
being widely different; still, the values serve our purpose technically. 
I found the following: 
| : | Electric charge 
Optimal distance _ in coulombs per c.c. 
Benzol S57em: | 116-45<10—" 
Toluol inks | ve lie PS 
Xylol 40 , | 14.5 X10—1! 
Pseudocumol en” | 8258 10"! 
Durol 35 | 24.1 >< 10—" 
