274 ANNUAL OF SCIENTIFIC DISCOVERT. 



chemist has made during the past thirty years researches made specially 

 to trace odors to their material causes. He reviews in the following manner 

 the actioTi by which bodies exert their odors when properly mixed with 

 other odoriferous materials. 1st. Bodies, themselves odorant, disguise the 

 odors of other substances, as a strong light overpowers a feeble one. 2J. 

 Bodies, being themselves odoriferous, act in the manner of an acid in neu- 

 tralizing a base. 3d. Solid bodies may act by capillary affinity to absorb 

 odors, as is the case, for example, with charcoal. 4th. Other bodies act by 

 altering the constitution of the odorant substance, producing new com- 

 pounds cither odorless or nearly so. Such is the action of moist chlorine or 

 oxygenated water. 5th. Lastly, the action may be twofold, as in the case 

 of chlorine and ammonia, decomposing one portion and neutralizing the 

 other, without decomposition. 



Neutralization includes the largest class of cases ; thus the volatile odorous 

 acids are neutralized by alkalies to form odorless salts. Ammonia loses its 

 odor when united to an acid. The odors in such cases are truly neutralized, 

 since displacing the acids liberates again the odors, each in its own char- 

 acter. Examples of the destruction of odors are numerous and well known 

 to chemists. Sulphydric acid, for instance, is at once decomposed by chlo- 

 rine, and consequently disinfected. Ammonia, by the action of chlorine, 

 offers an example of both neutralization and destruction of odors, because 

 at the same time we have decomposition of one part of the base and the 

 neutralization of another part by the ehlorohydric acid formed. 



M. Chevreul proposes to define odors by means of a scale, analogous to 

 our notation of sounds, or for gradations of color by the chromatic diagram 

 (which last device we also owe to this savant). The great obstacle to this 

 plan is, the difficulty of employing the sense of smell as we employ that of 

 sight or hearing, a difficulty much increased by the toleration which the 

 smell soon acquires to odors becoming " blase." 



In 1830 he endeavored to take account of the changing odors exhaled by 

 the woad-vats during evaporation, if possible to define exactly the kind of 

 odor appropriate to each condition of the vat. He reached no positive re- 

 sults, although he detected in the dye-stuff bath five perfectly distinct odors: 

 the odor of ammonia, a sulphurous odor, a metallic odor, an aromatic odor, 

 clinging for many months to the woollen stuffs which had passed through 

 the woad-vat; and lastly, the odor of a volatile acid analogous to that of 

 animal matters in decomposition. M. Chevreul hoped to detect in these 

 odors of the dye-vats symptoms to guide the dyer in his art, as the physi- 

 cian finds new indications in his knowledge of symptoms depending on the 

 chemical nature of organic solids and liquids, if these symptoms can be cer- 

 tainly recognized by their odor. Thus he did not shrink from exposing him- 

 self to the most repulsive odors of the organism to reach his results. Having 

 often heard the odor of a cancer spoken of as characteristic, he examined it, 

 and recognized it as a compond of 1st, an ammoniacal odor, turning blue 

 a reddened test-paper. 2d, a feeble butyric odor. 3d, a heavy odor which is 

 familiar in the " trying out " of suet or lard. Xo specific odor exists, then, 

 in cancers, since the three odors recognized coexist in non-cancerous mat- 

 ters which the disease alters. He recognized these matters in the odor 

 of pus, and other products of animal origin, and he also detected in them a 

 sulphurous odor and a smell of fish, due probably to a compound ammonia. 



To all these odors he adds what he calls the stale-nauseous (fade nausea- 



