150 THE POPULAR SCIENCE MONTHLY. 



from which essence of Portugal is extracted. A great number of 

 vegetable odors belong exclusively to tropical plants, but the flora of 

 Europe furnishes a large proportion of them, and almost all the es- 

 sences used in perfumery are of European origin. England cultivates 

 lavender and peppermint largely. At Nimes, gardeners are particularly 

 attentive to rosemary, thyme, petit-grain, and lavender. Nice has the 

 violet for its speciality. Cannes extracts all the essences of the rose, 

 the tuberose, cassia (the yellow acacia), jasmine, and neroli. Sicily 

 produces lemon and orange ; Italy, bergamot and the iris. 



What, now, is the chemical nature of the odorous principles 

 in plants? The chemistry of to-day reduces almost all of them to 

 three categories of well-ascertained substances : hyclrocarburets, alde- 

 hydes, and ethers. We will endeavor to give a clear account of the 

 constitution of these three kinds of substances, and to mark their 

 place in the register of science. The hyclrocarburets are simple com- 

 binations of carbon and hydrogen, as, for instance, the petroleum-oils. 

 They represent the simple compounds of organic chemistry. As to 

 aldehydes and ethers, their composition is rather more complex ; be- 

 sides carbon and hydrogen, they contain oxygen. Every one knows 

 what chemists mean by an alcohol; it is a definite combination of 

 hydrogen, carbon, and oxygen, neither acid nor alkaline, which may 

 be regarded as the result of the union of a hydrocarburet with the 

 elements of water. Common alcohol, or spirits of wine, is the type of 

 the most important series of alcohols, that of the mono-atomic alcohols. 

 Chemists represent it by the formula C 2 H0, to indicate that a mole- 

 cule of it arises from the union of two atoms of carbon with six atoms 

 of hydrogen and one of oxygen. Independently of the alcohols, which 

 are of great number and vai - ying complexity, organic chemistry recog- 

 nizes another class of bodies, of which vinegar is the type, and which 

 receive the name of organic acids, to mark their resemblance to min- 

 eral acids, such as oil of vitriol or aqua-fortis. Now, every alcohol, on 

 losing a certain amount of hydrogen, gives rise to a new body, which 

 is called an aldehyde; and every alcohol, on combining with an acid, 

 produces what is called an ether. These rapid details allow us to un- 

 derstand precisely the chemical character of the essences or essential 

 oils which plants elaborate within their delicate tissue. Except a small 

 number among them which contain sulphur, as the essences of the 

 family of crucifers, they all present the same qualitative composition 

 carbon andhydrogen, with or without oxygen. Between one and another 

 of them merely the proportion of these three composing elements 

 varies, by regular gradations, but so as always to correspond either 

 to a hydrocarburet, or to an aldehyde, or to an ether. In this case, 

 as in almost the whole of organic chemistry, every thing is in the 

 quantity of the composing elements. The quality is of so little im- 

 portance to Nature, that, while following always the same laws, and 

 constantly using the same materials, she can, by merely changing the 



