molecular weight, 
volatility, 
3. lowering of the surface-tension of the solvent, the same factors 
being, to a certain degree, essential to render a substance odorous. 
I particularly wish to lay stress on the second and thé third factor 
by observing that odorous substances lower the surface-tension of 
water, that they are volatile, and that, on the contrary, not all 
volatile substances, lowering the surface-tension, must of necessity 
be odorous substances. If my view is correct we may rationally 
expect a relationship to exist between the smell intensity of a sub- 
stance and the intensity of the electrical phenomenon. This relation- 
ship will appear in its simplest form with homologous series. 
In the literature mention has been made of two homologous series 
that have been carefully studied as to smell intensity. They are the 
aliphatie alcohols to the fifth term and the fatty acids to the tenth. 
Passy’) determined the smallest quantity of matter, diffused in a 
litre of air, capable of arousing olfactory sensation. When we 
divide this smallest quantity, expressed in grams by the molecular 
weight, the reciprocal of the number is an index for the specific’ 
smell intensity. This leads to the following results. 
By plotting the molecular weights along the axis of the abscissae 
and the molecular smell intensities along the axis of the ordinates 
we get curves of a regular shape. 
Likewise graphs may be made of the electrifying power of the clouds. 
When we place a circular tin disc 50 em. in diameter, in the 
drift of an odour-solution from an earthed sprayer, at only 1 or 2 mm. 
DO _ 
TABLET. 
Aliphatic alcohols. 
| | | Log. mol. 
Terms gr peritre MOL. Speci. sme intens. 
Methylalcohol 1000. 10-6 32 0.032.108 0.51 
Ethyl (,; |  -250.10-6 46 0.18 .106 1.26 
Propyl _, 10 à 5.106 60 6 106 2.18 
Butyl 1.106 | 74 74 .106 3.87 
Isoamyl , —0,1.10--6 | kg 880 . 108 4.94 
') Jacques Passy. Comptes rendus 16 Mai 1892 and 1 Mai 1893. 
*) H. ZwaARDEMAKER in Ticersteptr’s Hdb. der physiol. Methodik. Bd. Ill, S, 57. 
