108 AROMATIC COMPOUNDS [ch. 



Expt. 104. To demonstrate that tannins ma.y he present in herbaceous as well as 

 woody plants. Extract some leaves, as in the last experiment, of Scarlet Geranium 

 {Pelargonium zonale) and test for tannin. 



Expt. 105. To demonstrate that tannins may he present in petals and fruits, in 

 addition to other parts of the plant. Extract and test for tannins as in the last experi- 

 ment, using petals of Pelargonium zonale. Common Paeony {Paeonia officinalis) or 

 Kose (any garden variety), inflorescence of Flowering Currant {Rihes sanguineum), 

 flowers of Horse Chestnut {Aesculus Hippocastanum) or pericarp of Sweet Chestnut 

 (Castanea). 



The " Essential Oils" and Resins. 



When plant tissues are suspended in water, a current of steam passed 

 through the suspension, and the distillate collected, a mixture of volatile 

 substances will be found in the distillate and these can be separated from 

 the water by various methods. Such a mixture of organic volatile pro- 

 ducts constitutes an "essential oil." The classification is purely arti- 

 ficial, as the mixture is heterogeneous and contains substances of very 

 different chemical constitution. Since, however, the majority of "oils" 

 consist largely of aromatic compounds, they are included in the present 

 chapter. In many cases the " essential oil " contains some product of 

 commercial value. About two hundred and fifty plants, representing 

 between fifty and sixty Natural Orders, provide definite " oils," most of 

 which are prepared commercially. 



The chemical substances found in "essential oils" can be broadly 

 classed as follows (see also p. 82). 



1. The terpenes, which are complex, unsaturated (usually aromatic) 

 hydrocarbons frequently of the formula, CjoHig, e.g. pinene, limonene, 

 caryophyllene and phellandrene. 



2. Alcohols derived from the terpenes, e.g. borneol, menthol, citro- 

 nelloP, geraniol^ and linaloP; corresponding aldehydes, e.g. citronellal^ 

 and other aromatic aldehydes, e.g. cinnamic aldehyde. 



3. Esters of the above alcohols, e.g. bornyl acetate, geranyl acetate, 

 linalyl acetate and menthyl acetate ; also esters of other aromatic acids, 

 e.g. methyl salicylate. 



4. Phenols of high molecular weight, e.g. thymol, carvacrol and 

 eugenol. 



The following provide some examples of " essential oils " : 

 " Oil of turpentine," from species of Pinus, Larix and Abies, contains 

 pinene. 



The compound is aliphatic. 



