ESSENTIAL OILS. 



ESSENTIAL OILS. 



9U4 



The origin of this sect is uncertain. Some writers consider them 

 the same as the Assidians, or Chasidiiu, who are mentioned in 

 1 Mace, ii 42; vii. 13. It would appear from the account of Pliny 

 (' Nat Hist.' v. 17) that their principal society was on the western side 

 of the Dead Sea ; ami that from this society other smaller ones after- 

 wards proceeded, and spread themselves over Palestine, Syria, and 

 Egypt. Their numbers were never considerable : according to Philo 

 ami Joaephua, there were only 4000 in Palestine. 

 * The Essenes of Egypt were divided into two sects : the practical 

 Essence, whose manner of life was the same as the Esaenea of Palestine ; 

 and the contemplative Essence, who were also called TherapeirUc. 

 Both sects maintained the same doctrines, but the latter was distin- 

 guished by a more rigid mode of life. 



From a passage in Eusebiui ('Hist. Eccles.' ii. 17), it has been 

 argued by Bellariuine, Baronius, and other Roman Catholic writers, 

 that the Therapeutic were Christian monks formed into a society by 

 St. Hark, who was the founder of the Christian church at Alexandria. 

 But it is evident from the account of Philo, that the Therapeutic 

 were not Christians, but Jews. 



It has been supposed, with considerable probability, that the early 

 Christians derived many of their customs and opinions from the 

 Essenes. Mr. Taylor, the editor of Calmet's ' Dictionary to the Bible,' 

 gives many reasons for believing that John the Baptist belonged to 

 this sect. 



ESSENTIAL OILS, the odorous principles of plants, called also 

 Volatile Oils, to distinguish them from the non-volatile or fixed oils. 

 [FIXED OILS.] The present article will be devoted to a consideration 

 of their sources, methods of production, uses, and general physical 

 and chemical properties, together with an alphabetical list of those 

 known up to the present time, including the specific characters of each, 

 or references to other articles in this Cyclopaedia where those characters 

 are more fully detailed. 



Sourcet. Essential oils are not peculiar to any particular part of 

 plants. They may reside in the root, stem, leaf, flower, fruit, or seed. 

 They are generally contained in special cavities called receptacles of 

 secretion. These cavitites are frequently larger than the surrounding 

 cells, and indeed may often be seen with the naked eye. The dotted 

 appearance of the rind of the orange and lemon, and of the leaves of 

 the myrtle and St. John's wort [HYPERICUM, in NAT. HIST. Div.] is due 

 to the presence of numerous oil cavities. The cellular tissue forming 

 the walls of the cavities is in many cases so compact that the plant 

 may be dried and kept for several years without much of the oil being 

 dissipated. 



In nearly all instances the essential oils exist ready formed in 

 plants. In the bitter almond and black pepper, however, contact with 

 water is necessary to the production of the oil. Some other plants also, 

 as milfoil, plantain, nettle, and centaury, which naturally have little 

 or no odour, appear to undergo, when sprinkled with water, a kind of 

 fermentation by which abundance of essential oil is produced. Finally, 

 during the putrefaction of many vegetable matters, peculiar essential 

 oils are generated. 



Methods of Production. In nearly all cases essential oils are ob- 

 tained by a process of distillation. The plant, or that part of it from 

 which the oil is to be extracted, is usually macerated for a few hours 

 with four or five times its weight of water in a still furnished 

 with a false bottom. Heat being applied, and the contents of the 

 still brought into an active state of ebullition, the essential oil is 

 volatilised along with the steam, and the vapours being condensed in 

 any suitable way [CONDENSER] will, if the oil is present in sufficient 

 quantity, separate into two portions, one a saturated solution of the 

 oil in water, and the other a layer of the essential oil itself. The oil 

 being collected by any suitable contrivance, the water should be 

 occasionally returned to the still, and the distillation continued until 

 the oil ceases to come over. The object of having a false bottom to 

 the apparatus is to prevent portions of the plant from coming into 

 immediate contact with the heated surface of the still, thus avoiding 

 an unpleasant tarry taste and odour that would be communicated to 

 the oil by volatile substances evolved from the overheated vegetable 

 matter. The same end is arrived (at by enclosing the ingredients 

 acted upon in a bag, and so suspending the whole that it shall not 

 touch any portion of the still. Even more advantageous is a plan 

 now frequently adopted, of blowing [steam from a perforated coil 

 pipe through the materials to be acted upon, and condensing the 

 vapours as before. 



The water used in the above process dissolves a small portion of 

 the oils, forming solutions that are used in medicine as vehicles for 

 active preparations. Where it is required that these waters should 

 be preserved, every trace of the excess of oil should be carefully 

 removed; in some cases, redistillation of the water without the 

 pretence of the herb is beneficial. 



If the water is not needed, the oil contained in it may be re- 

 covered by adding chloride of sodium to saturation, essential oils 

 being but (lightly soluble in the solution thus formed. Or the water 

 may be agitated with ether, which will dissolve out the oil ; the oil 

 a then readily obtained by distilling off the ether. 



In a few instances the essential oil of a plant cannot be extracted 

 by distillation, on account of the injurious action of heat upon it, or 

 because of its smallness in quantity. In that case, the substances to 



be operated upon may be placed in layers alternate with cloths satu- 

 i ! ,1 with an inodorous fixed oil, such as oil of poppies, and the cloths 

 after a time submitted to strong pressure. The essential oil will then 

 be found to have dissolved in the fixed oil, to which it will comiiiuni 

 cate its characteristic odour, and from which it may, if necessary, be 

 separated by agitation with alcohol. 



The oils of lemon and orange may be extracted by simple pressure 

 of the rind of the fruit. 



Uut. The most extensive use of essential oils is in the fabrication 

 of perfumes. Considerable quantities are also used in medicine, as 

 topical or gastro-intestiual stimulants. 



On account of the essential oil they contain, plants, or certain parts 

 of them, are used to flavour liqueurs, confectionery, salads, savoury 

 dishes, soups, &c. 



Physical Propertici. The colour of essential oils is variable. The 

 portions first obtained in the process of distillation are sometimes 

 quite colourless, the later portions yellow or brown. These por 

 are however generally mixed together for commerce, so that essential 

 oils are seldom seen without colour. Moreover nearly all the essential 

 oils darken in colour on exposure to light and air. A few of them are 

 green, and two or three of a blue colour. The essential oils have 

 characteristic odours more powerful, but seldom as pleasant as that of 

 the plants from which they are obtained. Their taste is hot and 

 irritating. They have not the well-known unctuous feel that the 

 fats and fixed oils possess when rubbed between the fingers, but on the 

 contrary, are rough and harsh. They are nearly all lighter than water ; 

 a few however are heavier. The temperature at which the essential 

 oils assume, on the one hand, the solid state, and on the other, the 

 state of vapour, is very inconstant. This is explained by the fact 

 that they are usually mixtures in variable proportions of a pure 

 hydrocarbon, or elaopten, with an oxygenated hydrocarbon, or /(;"/ 

 the former commonly boiling at about 820 Fahr., the latter bi ! 

 390 and 465. Some of the essential oils are solid at temperatures 

 below 60 Fahr., others require to be cooled several degrees below the 

 freezing point of water before congelation occurs. The elaeopten may 

 generally be roughly separated from the stearopteu by cooling the 

 oil gradually. In the air the essential oils burn with a bright flame 

 accompanied with much soot. 



Chemical Properties, Exposed to the air, essential oils absorb oxygen, 

 and are slowly converted into resinous matters. During this process 

 carbonic acid is sometimes evolved. Light favours the action. Essen- 

 tial oils are soluble in ether and alcohol, and to a slight extent in 

 water. They are not soluble in caustic alkalies, and, with the excep- 

 tion of clove, pimento, and cinnamon-leaf oils, are not capable of saponi- 

 fication. They dissolve fixed oils, fats, and resins, with which tin 

 not unfrequently adulterated ; such fraud may, however, be easily 

 detected by exposing a drop of the suspected oils on blotting-paper ; 

 if pure it will evaporate in a short time without leaving any stain ; if 

 mixed with either of the above substances, a greasy stain will be left 

 on the paper. On passing the vapour of an essential oil over fused 

 hydrate of potash, it is usually oxidised to an acid body that combines 

 with the alkali, hydrogen gas being at the same time evolved. Chlo- 

 rine, bromine, and iodine act upon and replace hydrogen in most of the 

 essential oils. Nitric acid rapidly oxidises them. 



Composition. The ultimate chemical composition of essential oils is 

 carbon, hydrogen, oxygen, and sometimes sulphur. In chemical and 

 pharmaceutical treatises they will usually be found arranged in three 

 divisions, according to their proximate composition : 1. Pure hydro- 

 carbons ; 2. oxidised hydrocarbons ; 3. oils containing sulphur. 1 . 

 The pure hydrocarbons are nearly all isomeric and metameric, their 

 molecule being represented by C.JD H 10 . Such are termed m//i/./iw/. ;/.< 

 or terebenes, oil of turpentine being one of the members. Equal weights 

 yield equal volumes of vapour; the specific gravity of them all is alumi 

 860, and their boiling points range near 320 Fahr. They all absorb 

 hydrochloric acid gas forming with it artificial camphors [Ti HPI NTI.NH; |, 

 and combine with water, forming solid bodies still more closely resem- 

 bling camphor. Exposed to tho air, they absorb oxygen, and are con- 

 verted into resins. A few of the pure hydrocarbons have a compo-it inn 

 differing from C^,, H la . 2. Oxidised hydrocarbons. Some of these are 

 solid, forming the so-called camphors or stearopteiM [CAMPHOR], Others 

 present the characters of an aldehyde, an alcohol, or an acid. The 

 aldehydes, or hydrides as they are sometimes called, combine and form 

 crystalline compounds with the bisulphites of the alkalies. 3. oils 

 containing sulphur. The members of this division are compounds of 

 the radical ALI.YI.. 



Tests for ascertaining the purity of the principal essential oils will In- 

 found described under the respective names of the latter. The neces- 

 sary experiments, however, belong to the higher branches of pharma- 

 ceutical chemistry, and for this reason : that ex]-n.sive oils are usually 

 sophisticated with cheap ones, and from the great similarity that exists 

 between many of them, both in physical and chetnii-al pro]>ertiea, it 

 necessarily follows that the detection of surh ,-idulti>r.-itions is difficult. 

 See ' Tests of the purity and adulteration of the volatile oils,' in ' Jahrb. 

 fur praktische Pharm., Juli. 1849,' and ' Pharmaceutical Journal,' vol. 

 ix., old series, p. 575-580. 



fssentiai oil of achUlea, is obtained from the plant yarrow, or milfoil. 

 [Acmu.EA, in NAT. HIST. Div.] It i of a beautiful blue colour. 



Euentialoil of aUiarvi. The alllaria officituUi* [EBYSIM0M, in NAT. 



