FERMENTS AND MISCELLANEOUS PRODUCTS 95 



(p. 47), includes any waxes that may be present. The latter 

 are not digested by animals and have no nutritive value. 



Volatile or Essential Oils. The so-called essential oils 

 or essences of plants are also unctuous substances of low 

 specific gravity a few are heavier than water. Most of them 

 are insoluble in water, but soluble in alcohol, ether, and other 

 common solvents for fats. They exhibit characteristic aromatic 

 odours, and usually have a strong piquant taste. The presence 

 of essential oils in vegetable matter imparts something of these 

 qualities to it, and often renders it more attractive to animals 

 as food. In other words, they serve as natural condiments. A 

 few, e.g. oil of bitter almonds, occur in the plants in the form 

 of glucosides or other non-odorous compounds, but the majority 

 occur as such or mixed with oleoresins. 



The essential oils are distinguished from the true fats or 

 fixed oils by the fact that they are volatile. They can be 

 distilled without decomposition and leave no permanent 

 translucent strain on paper. Constitutionally they are very 

 different. They are not glycerides. Some chiefly the 

 essences of fruits and flowers are esters, but the acids and 

 alcohols of which they are composed are of low molecular 

 weight, and the latter are monohydric. More commonly they 

 are hydro-carbons, alcohols, phenols, aldehydes, ketones, or 

 acid anhydrides. Nitrogen, or sulphur, or both, enter into the 

 composition of some. The majority are mixtures of several 

 compounds. The following examples will serve to illustrate 

 the nature of the chief constituents of some of the well-known 

 essential oils. 



Essence of pineapple contains ethyl butyrate, C 4 H 7 O2.C 2 H 5 . 

 Essence of Jargonelle pear contains amyl acetate, C 2 H 3 O2.C5H n . 

 Menthol, which occurs in oil of peppermint, is an alcohol. 

 Cinnamic aldehyde, C 6 H 5 CH:CHO, is a constituent of the oil 

 of cassia. Thymol, C 6 H 3 (CH 3 )(C 3 H 7 )OH, which occurs in oil 

 of thyme, and eugenol, C 6 H 3 (C 3 H 5 )(OCH3)OH, are both 

 phenols. Oil of garlic is allylsulphide, (C 3 H 5 ) 2 S, and mustard 

 oil is allylisothiocyanate, C 3 H 5 NCS. 



The last occurs in the form of a glucoside, potassium 

 myronate (p. 89), in mustard seeds. In excessive quantity it 



