456 



KNOWLKDGi:. 



December, 1912. 



these fruits are [iressed against a sponge, wliicli 

 lireaks tlie oil vessels and extracts the li(]uid, the 

 latter beiii{; periodically s<iueezed out. This is tlie 

 process largely made use of in Sicily for ohtainiii},' 

 oil of lemon, and the expressed oil, so obtained. 

 is purified by filtration. 



The second method -" extraction " — consists in 

 remo\ing the oil contained in the particular material 

 by means of a solvent (chloroform, carbon bisuli^hidc, 

 mctliyl chloride, and so on), which, being usually 

 volatile, is afterwards recovered by distillation, the 

 remaining oil being freed from the resinous and 

 colouring matter, also dissolved by the above-men- 

 tioned liquids, either by rectification under reduced 

 pressure or distillation in steam. A further method 

 of removing the odorous constituents of plants is 

 performed by treatment with a non-volatile substance 

 (lard or other fat) : this method will be referred to 

 later when we come to consider the preparation of 

 perfumes. The distribution of essential oil in plants 

 may be either general or local, the pine affording an 

 example of the former, while in the rose it isconlined 

 to the leaves of the flower, in the cinnamon to the 

 bark, and in the orange to the pericarp of the fruit. 



The volatile oils, which in many cases are 

 katabolically-produced secretion or excretion pro- 

 ducts, are found either in closed cells, or in special 

 reservoirs in the plant tissues. The origin of the 

 latter oil ducts or vessels mav be either lysigenous 

 or schizogenous, these botanical terms expressing 

 respectively the absorption or separation of series of 

 cells to form more or less definite cavities or passages. 

 Figure 487 illustrates a lysigenous cavity in the 

 pericarp of the orange, w ith a drop of ethereal oil, 

 and Figure 486 a schizogenousl\--formed oleo-resin 

 duct of a species of Piiiiis, with its la\er of thin- 

 walled parenchymatous epithelial cells. 



In the ho[) the oil is found in dermal glands of 

 capitate and peltate form, while in the Umbelliferae 

 it is stored in tube-like structures, known as vittae. 



FlGiKE 4>S2. — .Vii curly form of the worm Condenser. 



chiefl)- in the fruits, the latter usually possessing two 

 such vessels on the commisural and four on the other 

 surface of each mericarji, although in the anise manv 

 more (usually twenty to thirty) vittae arc discernable 

 in either half of the cremocarp. 



.Although most essential oils pre-exist in the plant 

 tissues, many owe their formation to the hvdrolvsis of 

 substances of a glucf)sidal nature, brought about bv 

 ferments. 



Fxamples of this (■lu!mical ac:tion are afforded bv 

 the production of the volatile oils of black mustard 

 (seed) and bitter almond (seed). In the former the 

 enzyme is a substance called myrosin, while the 

 glucoside is represented by sinigrin : in the latter 

 emulsin and amygdalin illustrate the same classes of 



Figure 483. 



Steam distillation apparatus used in England 

 for small quantities. 



substances. No action takes place in the seeds of 

 these plants on account of their active principles 

 being situated indifferent cells: but when these cells 

 are ruptured in the presence of water the reactions 

 indicated by the following equations occur : — 



Ci„H„;KNS,0,+ H,0 = C3H5CSN + CcH„0„4-KHSO, 

 Sinigrin ^-iVUyl Isothiocyanate + Glucose 



+ Potassium Hydrogen Sulphate 

 C.2qH>7NOu4-2H,0 = 2C,;H,..0,;+C,H.,-CH04-HCX 

 Amygdalin Benzaldehyde-|- Hydrocyanic .-Vcid. 



In the latter case the poisonous hydrocyanic acid 

 has to be removed b\- suitable treatment before the 

 oil is safe for use as a flavouring agent, when it will 

 consist of practically pure benzaldehydc. When the 

 oils of black mustard and bitter almond are manu- 

 factured in large quantities, the seeds are first 

 subjected to a process of maceration with water, to 

 allow the formation of characteristic odorous 

 principles, indicated in the above eejuations. 



\\'i;\\ill now ili\crt our attention from the jiro- 

 duction to a \ery brief review of the more common 

 constituents of the essential oils. 



These may be roughly classified under the follow- 

 ing heads: — (1) The Terpenes, (2) .Mcohols and 

 esters, (J) Phenols and their derivatives, and (4) 

 -Mdehydes and ketones. 



It is proposed to outline the main properties of 

 these great groups of organic compounds, and to 

 illustrate, by the aid of Table 50. their occurrence 

 in a few well-known volatile oils. 



( 1 1 The luilrocarbons, known as the terpenes, 

 along with their derivatives, constitute the most 



