CHEMICAL SCIENCE. 275 



bonde), which appears in well-water that has stood some days in a vessel in 

 which have been placed egg-shells impregnated with albumen. 



We may be permitted to add to these interesting facts some others which 

 we submit to the distinguished author of the chromatic circle and researches 

 on the fatty bodies. 



1. If an odorous substance can be neutralized or destroyed by another 

 odorant body, there are others destitute of odor, which, by union, produce 

 odorant substances. 



(To this class of odorless bodies belong 0, S, Se, Te, C, H, As, 1ST, .and we 

 might add P, which is odorless unless combined.) 



2. Likewise there are odorless bodies which have become odorant by union 

 with others endowed with odor. 



It is thus with oxalic, malic, butyric, racenic, citric, sorbic (the acid re- 

 cently discovered by Hoffman), boric, silicic acids, all odorless, which how- 

 ever produce, with the elements of alcohol, ethers more or less aromatic. 



3. It is necessary to distinguish those bodies which act mechanically on 

 the olfactory membranes (for example, CHI, F1H, BrH, IH, and the vapors 

 of NOs-HiO, SOa HO) from those which exert a physiological influence (for 

 example, Cl, Br, I, NO-i, 802, the hydrocarbons, the essential oils, etc). 



4. It is necessary also to distinguish bodies having an odor proper, that 

 is, an odor which exists when they form compounds with other bodies (for 

 example, arsenic). The arsenical odor is recognized in AsHs, AsBrs, and 

 in the cacodyl series. Tin is another example. The odor of tin charac- 

 terizes a large number of stannic compounds. Sulphur: thus SO-'SH, S-C, 

 SXH.3, SCI, etc., are distinguished by a more or less sulphurous odor. 



We might also mention naphthaline, benzine, and other hydrocarbons and 

 organic radicals. 



We see that this group of bodies, characterized by a peculiar odor, em- 

 braces those elements which, like sulphur, arsenic and phosphorus, are desti- 

 tute of odor; that is, their odor is manifest only in combination. If we exam- 

 ine this phenomenon, we observe () that elementary bodies are usually 

 destitute of odor; (6) that in general the least odorant compounds are gener- 

 ally oxygen compounds ; (c) highly odorant compounds are usually those con- 

 taining hydrogen. These seemingly singular facts may to a certain extent be 

 explained, when we remember that, in general, chemical compounds become 

 less volatile as they fix oxygen, while by union with hydrogen they become 

 more volatile. But these considerations do not explain all; they do not tell us 

 why CO and CO2are odorless gases, while Ci2H, C26Hs,Ci-;H6, etc., are odorant. 



Moreover, the perfumes, properly so called, as musk and the aromatic 

 essences, rose, lemon, orange, bergamot, lavender, etc., are eminently hy- 

 drogen compounds. They are not at all volatile; and some of them may be 

 exposed to the air for years, exhaling odor all the time, with no sensible loss 

 of weight. Among these are the perfumes isolated by Milon in ISofi. The 

 cause of odors is not referable exclusively to the phenomenon of volatility, 

 although, as a general thing, the odor of most bodies is developed when they 

 are volatilized. 



Hydrogen must be considered, par excellence, the exciting cause of odors. 

 This element possesses, above all other substances, the peculiar property of 

 developing odors, even with odorless bodies, as nitrogen, carbon, selenium, 

 tellurium, phosphorus, etc., and a great number of compounds of these and 

 other elements. Oxygen, on the other hand, appears to act the chief part in 

 the perception of odors ; it seems indeed proved that odors are not recog- 



