236 ESSENTIAL OR VOLATILE OfLS. 



The volatile oils are not easily obtained by pressure ; but are 

 readily driven off by heat ; but this must not be so great for 

 the most diffusible, as that of boiling water. To communicate 

 the fragrance of flowers to a fixed oil, cotton soaked in it is 

 placed in alternate layers with the flowers whose scent is to be 

 obtained, so as to fill a close vessel, which is then placed in hot 

 water for twenty-four hours ; during this time, the fixed oil will 

 have imbibed the rich perfume of the flowers, and it is then 

 separated from the cotton by pressure. 



374. Those essential oils which are somewhat less volatile, may 

 be obtained by distillation, in the same manner as spirits. The 

 substances which yield them are put into a vessel, with water to 

 prevent their being over-heated. When the water is boiled, the 

 oil passes away with the steam ; and, when both are condensed, 

 it floats upon the surface of the water. A large number of oils, 

 possessing great fragrance and strong taste, may thus be obtained 

 from different kinds of plants ; and these oils are used in per- 

 fumery, in confectionery, and in medicine. The oils of Roses, 

 Lavender, Chamomile, &c. are distilled from the flowers ; those 

 of the various plants of the Mint kind Peppermint, Spearmint, 

 Pennyroyal, &c., from the leaves and stems, which contain it 

 in a number of little receptacles near their surface; that of 

 Sassafras from the wood ; that of Cinnamon from the bark ; 

 that of Caraway, Anise, Fennel, and other Umbelliferous plants, 

 from the coats of their seeds, in which they are stored up in 

 little receptacles ; that of Lemons, from similar receptacles in 

 the rind of the fruit ; and that of Nutmeg, from the seed itself. 

 Many of these oils contain Camphor, which may be separated 

 from them by exposure to cold. Sometimes the secretion of 

 volatile oil is so abundant, as to make itself perceptible in the 

 atmosphere around, to other senses besides smell. Thus the 

 Fraxinella gives off so much from its leaves, that the air in its 

 neighbourhood is highly inflammable in warm weather. There 

 are some substances, which seem to contain the materials of an 

 essential oil, rather than the oil itself. Thus when water is 

 added to flower of Mustard, an acrid and volatile oil is produced, 



