Page:Popular Science Monthly Volume 6.djvu/156

144 solid or fluid, placed on moistened glass, or in a saucerful of water, instantly act on those molecules of the liquid which they touch, and repel them more or less, producing a vacuum. He judged that this method might serve to make odors sensible to sight, and enable us to distinguish odorous from inodorous bodies. These movements of odorous bodies on the surfaces of liquids, of which camphor particularly gives so curious an instance, have lately been studied with the greatest care by a French physiologist, with a view to establishing a theory of odors. With this purpose Liégeois has examined most of the odoriferous substances, and has ascertained that almost all of them perform various motions of circulation and displacement on the surface of water, resembling those noted with camphor. Some act precisely as camphor does. Among these are benzoic acid, succinic acid, the rind of bitter oranges, etc. With others, motion soon stops, for they are quickly surrounded by an oily film which keeps them confined. Some must be reduced to powder before the phenomenon takes place. As regards odorous liquids, it occurred to Liégeois to saturate very light and spongy seeds, themselves odorless, with them, and he then found, on throwing the seeds on water, that circulatory and displacing movements took place, as with other substances. He concluded, from a series of experiments methodically tried, that the motions in question must be attributed, not to a release of gas, acting in the manner of a recoil, but simply to the separation and rapid diffusion, within the water, of the odorous particles. The volatility of substances cannot be admitted to have any part in explaining the phenomenon. It depends wholly on the affinity of fluids for the odorous particles, and also for those of fatty matter. Liégeois found, for instance, that a drop of oil put on the surface of water, without sensibly lessening in size, emits an enormous quantity of microscopic droplets, which are diffused through the mass of the water. Aromatic essences produce a like effect. Though insoluble in water, they have a powerful tendency to disperse themselves throughout it, and water that receives a very small quantity of the odoriferous principle, in the shape of extremely fine powder, has enough to gain their perfume completely. Liégeois's experiments give proof of the most diligent labors and of praiseworthy sagacity. Science has accepted them with satisfaction, and, after employing them usefully, will preserve the memory of their author, taken away in the flower of his age, at the outset of a noble career as a physiologist and surgeon.

It seemed, to quote his words, as though in these experiments we were assisting at the formation of the odorous molecules. Those delicate atoms emitted from odorous substances and diffused through the atmosphere are, in fact, the very same that impinge on our pituitary membrane, and give us the sensation of odors. Moreover, facts long ago observed display this revealing action, so to call it, of water upon odors. At morning, when the verdure is moist and the flowers