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on to the last, when the grains are sufficiently bruised, crushed and ground. The distance between tnc rollers can be easily regulated so that the seed leaving the bottom roller has the desired fineness. The comminuted mass, forming a more or less coarse meal, is either expressed in this state or subjected to a preliminary heating, according to the quality of the product to be manufactured. For the preparation of edible oils and fats the meal is expressed in the cold, after having been packed into bags and placed in hydraulic presses under a pressure of three hundred atmospheres or even more. The cakes are allowed to remain under pressure for about seven minutes. The oil exuding in the cold dissolves the smallest amount of colouring matter, &c., and hence i.-> suffered least in its quality. Oils so obtained arc known in commerce as " cold drawn oils," "cold pressed oils," "salad oils," " virgin oils."
By pressing in the cold, obviously only part of the oil or fat is recovered. A further quantity is obtained by expressing the seed meal at a somewhat elevated temperature, reached by warming the comminuted seeds or fruits either immediately after they leave the five-roller mill, or after the "cold diawn oil has been taken off. Of course the cold pressed cakes must be first disintegrated, which may be done under an edge-runner. The same operation may be repeated once more. Thus oils of the " second expression " and of the "third expression" are obtained.
In the case of oleaginous seeds of low value (cotton-seed, linseed) it is of importance to express in one operation the largest possible quantity of oil. Hence the bruised seed is, after leaving the fiveroller mill, generally warmed at once in a steam-jacketed kettle fitted with a mixing gear, by passing steam into the jacket, and sending at the same time some steam through a rose, fixed inside the kettle, into the mass while it is being agitated. This practice is a survival of the older method of moistening the seed with a little water, while the seeds were bruised under edge-runners, so as to lower the temperature and facilitate the bursting of the cells. The warm meal is then delivered through measuring boxes into closed prcssbags (" scourtins" of the " Marseilles" press), or through measuring boxes, combined with an automatic moulding machine, into cloths open at two sides (Anglo-American press), so that the preliminarily pressed cakes can be put at once into the hydraulic press. In the latest constructions of cage presses, the use of bags is entirely dispensed with, a measured-out quantity of seed falling direct into the circular press cage and being separated from the material forming the next cake by a circular plate of sheet iron. The essentials of proper oil pressing arc a slowly accumulating pressure, Bo that the liberated oil may have time to flow out and escape, a pressure that increases in proportion as the resistance of the material increases, and that maintains itself as the volume of material decreases through the escape of oil.
Numerous forms of hydraulic presses have been devised. Horizontal presses have practically ceased to be used in this branch of industry. At present vertical presses arc almost exclusively in vogue; the three chief types of these have been already mentioned. Continuously working presses (compression by a conical screw) have been patented, but hitherto they have not been found practicable. Of the vertical presses the Anglo-American type of press is most in use. It represents an open press fitted with a number (usually sixteen) of iron press plates, between which the cakes are inserted by hand. A hydraulic ram then forces the table carrying the cakes against a press-head, and the exuding oil flows down the sides into a tank below. The " Marseilles press" is largely used in the south of France. There the meal is packed by hand in " scourtins," bags made of plaited coco-nut leaves—replacing the woollen cloths used in England. The packing of the press requires more manual labour than in the case of the Anglo-American press; moreover, the Marseilles press offers inconvenience in keeping the bags straight, and the pressure cannot be raised to the same height as in the more modern hydraulic presses. Oil obtained from heated meal is usually more highly coloured and harsher to the taste than cold drawn oil, more ofthe extractive substances being dissolved and intermixed with the oil. Such oils are hardly suitable for edible purposes, and they are chiefly used for manufacturing processes. According to the care exercised by the manufacturer in the range of temperature to which the seed is heated, various grades of oils are obtained.
In the case of those seeds which contain more than 40% of oil, such as arachis nuts and sesame seed, the first expression in pressbags leads to difficulty, as the meal causes " spueing, if. the meal exudes and escapes from the press. Hence, in modern installations, the first expression of those seeds is carried out in so-called cage (clodding) presses, consisting of hydraulic presses provided with circular boxes or cages, into which the meal is filled. These cages or boxes are either constructed of metal staves held together by a number of steel rings, or consist of one cylinder having a large number of perforations. The presses having perforated cylinders, although presenting mechanically a more perfect arrangement, are not preferable to the s cages formed by staves, as the holes become easily clogged up
the meal, when the cylinder must be carefully cleaned out. Modern improvements, with a view to cheapening of cost, effect the transport of the cages from one press battery to another on rails. In order to dispense even with the charging of the presses by hand, in some systems the cages are first charged in a preliminary press,
from which they are transferred mechanically by a swinging arrange* m. nt into the final press.
Whilst the meal is under pressure the oil works its way to the edge of the cake, whence it exudes. For this reason an oblong form is the most favourable one for the easy separation of the oil. The edges of the cakes invariably retain a considerable portion of oil; hence the soft edges arc pared off, in the case of the oblong cake in a cakeparing machine, and the parings are returned to edge-runners, to be ground up and again pressed with fresh meal. Through the introduction of the cage (clodding) presses circular cakes have become fashionable, and as the material of these presses can be made much stronger and therefore higher pressure can be employed, more oil ia expressed from the meal than in open presses. The oil flowing from the presses is caught in reservoirs placed under the level of the floor, f rom^which it is pumped into storage tanks for settling and clarifying.
Extraction by Solvents.—The cakes obtained in the foregoing process still retain considerable proportions of oil, not less than 4 to 5%—usually, however, about 10%. If it be desired to obtain larger quantities than are yielded by the above-described methods, processes having for their object the extraction of the seeds by volatile solvents must be resorted to. Extraction by means of carbon bisulphide was first introduced in 1843 by Jesse Fisher of Birmingham. Thirteen years later E. Deiss of Brunswick again patented the extraction by means of carbon bisulphide (Eng. Pat. No. 390* 1856), and added "chloroform, ether, essences, or benzine or benzole to the list of solvents. For several years afterwards the process made little advance, for the colour of the oils produced was higher and the taste much sharper. The oil retained traces of sulphur, which showed themselves disagreeably in the smell of soaps made from it, and in the blackening of substances with which it was used. Of course, the meal left by the process was so tainted with carbon bisulphide that it was absolutely out of the question to use the extracted meal as cattle food. With the improvement in the manufacture of carbon bisulphide, thfsc drawbacks have been surmounted to a large extent, and the process of extracting with carbon bisulphide has specially gained much extension in the extraction of expressed olive marc in the south of France, in Italy and in Spain. Yet even now traces of carbon bisulphide are retained by the extracted meal, so that it is impossible to Iced cattle with it. Carbon bisulphide ia comparatively cheap, and it is heavier than water, hence there are certain advantages in storing so volatile and inflammable a liquid. But owing to the physiological effect carbon bisulphide has on the workmen, coupled with the chemical action of impure carbon bisulphide on iron which has frequently led to conflagrations, the employment of carbon bisulphide must remain restricted. .In 1863 Richardson, Lundy and Irvine secured a patent (Eng. Pet. No. 2315) for obtaining oil from crushed seeds, or from refuse cake, by the solvent action of volatile hydrocarbons from "petroleum, earth oils, asphaltum oil, coal oil or shale oil, such hydrocarbons being required to be volatile under 212° F." Since that time the development of the petroleum industry in all parts of the world and the large quantities of low boiling-point hydrocarbons—naphtha —obtained from the petroleum fields, and also the improvements in the apparatus employed, have raised this system 01 extraction to the rank of a competing practical method of oil production. Of the other proposed volatile solvents ordinary ether has found no practical application, as it is far too volatile and hence far too dangerous. Carbon tctrachtoride, chloroform, acetone and benzene arc far too expensive. Carbon tetrachloridc would be an ideal solvent, as it ts non-inflammable and shares \vith carbon bisulphide the advantage of being heavier than water. Efforts have been made during the last few years to introduce this solvent on a large scale, but its high price and its physiological effect on the workmen have hitherto militated against it. At the present time the choice lies practically only between the two solvents, carbon bisulphide and naphtha (petroleum ether). Naphtha, is preferable for oil seeds, as it extracts neither resins nor gummy matters from the oil seeds, and takes up less colouring matter than carbon bisulphide. Yet even with naphtha traces of the solvents remain, so that the meal obtained cannot be used for rattle feeding, notwithstanding the many statements by interested parties to the contrary. It is true that on the continent extracted meal, especially rape meal from good Indian seed and palm kernel meal, arc somewhat largely used as food for cattle in admixture with press cakes, but in England no extracted meal is used for feeding cattle, but finds its proper use in manuring the land.
The apparatus employed on a large scale depends on the temperature at which the extraction is earned out. In the main two types of extracting apparatus arc differentiated, viz. for extraction in the cold and for extraction in the hot. The seed is prepared in a similar manner as for pressing, except that it is not reduced to a hne meal, so as not to impede the percolation of the solvent through the mass. In the case of cold extraction the seed is placed in a scncc of closed vessels, through which the solvent percolates by displacement, on the " counter-current " system. A battery of vessels is so arranged that one vessel can always be made the last of the scries to discharge finished meal and to be recharged with fresh meal, so that the process is practically a continuousonc. The solution of the extracted oil or fat is then transferred to a steam-heated still, where the solvtnt m driven off and recovered by condensing the vapours in a cooling coil, to be used again. The last remnant of volatile solvent in the oil is driven off by a current of open steam blown through the oil in the warm state. The extracting process in the hot is carried out in apparatus, the principle of which is exemplified by the well-known Sdhta extractor. The comminuted seed is placed inside a vessel conflicted with an upright refrigerator on trays or baskets, and is surrounded there by the volatile solvent. On heating the solvent with steam through a coil or jacket, the vapours rise through and around the meal. They pass into the refrigerator, where they arc condensed and fall back as a condensed liquid through the meal, percolating it as they pass downwards, and reaching to the bottom of the vessel as a more or less saturated solution of oil in the solvent. The solvent is again evaporated, leaving the oil at the bottom of the mad until the extraction is deemed finished. The solution of fat is Uvcn run off into a still, as described already, and the last traces of solvent arc driven out. The solvent is recovered and used again.
1A ith regard to the merits and demerits of the last two mentioned processes—expression and extraction—the adoption of cither will largely depend on local conditions and the objects for which the products arc intended. Wherever the cake is the main product, expmakm will commend itself as the most advantageous process. Where, however, the fatty material forms the main product, as in the case of palm kernel oil, or sesame and coco-nut oils from damaged seeds (which would no longer yield proper cattle food), the process of extraction will be preferred, especially when the price of oils is high. In some cases the combination of the two processes commends itself, as in the case of the production of olive oil. The fruits are expressed, and after the edible qualities and best class of oils for technical purposes have been taken off by expression, the remaining palp is extracted by means of solvents. This process is known under tbe name of mixed process (huiierie mixtc).
Refining and Bleaching.—The oils and fats prepared by any of the methods detailed above are in their fresh state, and, if got from perfectly fresh (" sweet ") material, practically neutral. If care be exercised in the process of rendering animal oils and fats or expressing oils in the cold, the products are, as a rule, sufficiently pure to be delivered to the consumer, after a preliminary settling has allowed any mucilaginous matter, such as animal or vegetable fibres or other impurities, and also traces of moisture, to separate out. This spontaneous clarification was at one time the only method in vogue. This process is now shortened by filtering oils through filter presses, or otherwise brightening them, e.g. by blowing with air. In many cases these methods still suffice for the production of commercial ous and fats.
In special cases; such as the preparation of edible oils and fats, a farther improvement in colour and greater purity is obtained by filtering tbe oils over charcoal, or over natural absorbent earths, inch as fuller's earth. Where this process does not suffice, as in tbe case of coco-nut oil or palm kernel oil, a preliminary purification in a current of steam must be resorted to before the final purification, described above, is carried out. Oils intended for use on the table which deposit " stearinc " in winter must be freed from such solid fats. This is done by allowing the oil to cool down to a low temperature and pressing it through cloths in a press, when a Empid oil exudes, which remains proof against cold—" winter oil." Host olive oils are naturally non-congealing oils, whereas the Tunisian and Algerian olive oils deposit so much "stearine" that they must be " demargarinated." Similar methods are empbyed in tbe production of lard oil, edible cotton-seed oil, &c. For refining oils and fats intended for edible purposes only the foregoing methods, which may be summarized by the name of physical methods, can be used; the only chemicals permissible are »nrali* or alkaline earths to remove free fatty acids present. Treatment with other chemicals renders the oils and fats unfit for consumption. Therefore all bleaching and refining processes involving other means than those enumerated can only be used for technical oils and fats, such as lubricating oils, burning oils, paint oils, soap-making oils, &c~
Bleaching by the aid of chemicals requires great circumspection. There is no universal method of oil-refining applicable to any and every oil or fat. Not only must each kind of oil or fat be considered as a special problem, but frequently even varieties of one and the same oil or fat are apt to cause the sqrpg difficulties as would a new individual. In many cases the purification by means of sulphuric acid, invented and patented
by Charles Cower in 1792 (frequently ascribed to Thenard), is still usefully applied. It consists in treating the oil with a small percentage of a more or less concentrated sulphuric acid, according to the nature of the oil or fat. The acid not only takes up water, but it acts on the suspended impurities, carbonizing them to some extent, and thus causing them to coagulate and fall down in the form of a flocculcnt mass, which carries with it mechanically other impurities which have not been acted upon. This method is chiefly used in the refining of Unseed and rape oils. Purification by means of strong caustic soda was first recommended as a general process by Louis C. Arthur Barrcswil, his suggestion being to heat the oil and add 2% to 3% of caustic soda. In most cases the purification consisted in removing the free fatty acids from rancid oils and fats, the caustic soda forming a soap with the fatty acids, which would cither rise as a scum and lift up with it impurities, or (all to the bottom and carry down impurities. This process is a useful one in the case of cotton-seed oil. As a rule, however, it is a very precarious one, since emulsions are formed which prevent in many cases the separation of oil altogether. After the treatment with sulphuric acid or caustic soda, the oils muse be washed to remove the last traces of chemicals. The water is then allowed to settle out, and the oils are finally filtered. The number of chemicals which have been proposed from time to time for the purification of oils and fats is almost legion, and so long as the nature of oils and fats was little understood, a secret trade in oil-purifying.chemicals flourished. With our present knowledge most of these chemicals may be removed into the limbo of useless things. The general methods of bleaching besides those mentioned already as physical methods, viz. filtration over charcoal or bleaching earth, are chiefly methods based on bleaching by means of oxygen or by chlorine. The methods of bleaching by oxygen include all those which aim at the bleaching by exposure to the air and to sunlight (as in the case of artists' linseed-oil), or where oxygen or ozone is introduced in the form of gas or is evolved by chemicals, as manganese dioxide, potassium bichromate or potassium permanganate and sulphuric acid. In the process of bleaching by means of chlorine cither bleaching powder or bichromates and hydrochloric acid are used. It must again be emphasized that no general rule can be laid down as to which process should be employed in each given case. There is still a wide field open for the application of proper processes for the removal of impurities and colouring matters without running the risk of attacking the oil or fat itself.
Oil Testing.—Reliable scientific methods for testing oils and fats date back only to the end of the 'seventies of the igth century. Before that time it was believed that not only could individual oils and fats be distinguished from each other by colour reactions, but it was also maintained that falsification could be detected thereby. With one or two exceptions (detection of sesame oil and perhaps also of cotton-seed oil) all colour reactions arc entirely useless. The modern methods of oil testing rest chiefly on so-called "quantitative" reactions, a number of characteristic "values" being determined which, being based on the special nature of the fatty acids contained in each individual oil or fat, assist in identifying them and also in revealing adulteration. These " values," together with other useful methods, are enumerated in the order of their utility for the purposes of testing.
The saponific.ation value (safxmificalt'on number) denotes the number of milligrams which one gramme of an oil or fat requires for saponification, or, in other words, for the neutralization of the total fatty acids contained in an oil or fat. We thus measure the alkali absorption value of all fatty acids contained in an oil or fat. The saponification values of most oils and fats lie in the neighbourhood of 195. But the oils belonging to the rape oil group are characterized by considerably lower saponification values, viz. about 175 on account of their containing notable quantities of erucic acid, C«H«iOj. In the case of those oils which do not belong to the rape oils and yet show abnormally low saponification values, (he suspicion is raised at once that a certain amount of mineral oils (which do not absorb
alkali and are therefore termed " unsaponifiable ") has been admixed fraudulently. Their amount can be determined in a direct manner by exhausting the saponified mass, after dilution with water, with ether, evaporating the latter and weighing the amount of mineral oil left behind. A few of the blubber oils, like dolphin jaw and porpoise jaw oils (used for lubricating typewriting machines), have exceedingly high sappnification values owing to their containing volatile fatty acids with a small number of carbon atoms. Notable also are coco-nut and palm-nut oils, the saponification numbers of which vary from 240 to 260, and especially butter-fat, which has a saponincntion value of about 227. These high »aponification values arc due to the presence of (glyceridcs of) volatile fatty acids, and are of extreme usefulness to the analyst, especially in testing butter fat for added marg.irinc and other fats. The*o volatile acids are specially measured by tnc Reicherl value (Retchtrt- Woltny value). To ascertain this value the volatile acids contained in 5 grammes of an oil or fat are distilled in a minutely prescribed manner, and the distilled-off acids are measured by litration with decinormal alkali. Whereas most of the oils and tats, vu. all thosr the sapomficaiion value of which lies at or below 195, contain practically no volatile acid>,t.£. have extremely low Reichcrt-Wollny values, all those oils and fata having saponincation values above 195 contain notable amounts of volatile fatty acids. Thus, the Rcickcrt-Metssl wlut ol butter-fat is 25-10, that of coco-nut oil 6-7, and of palm kernel oil about '-,'" This value is indispensable for judging the purity of a butter.
One of the most important values in oil testing is ihe iodine value, This indicates the percentage of iodine absorbed by an oil or fat when the latter is dissolved in chloroform or carbon tctrachlorkle, and treated with an accurately measured amount of free iodine supplied in the form of iodine chloride. By this means a measure is obtained of the unsatu rated fatty acids contained in an oil or fat. On this value a scientific classification of all oil* and fats can be based, as is shown by the above-given list of oil* and fats. The un&aturatcd fatty acids which occur chiefly in oils and fats are oleic acid, iixJinc value 90-07; crude acid, iocfine value 75-15; linolic actd, iodine value 181-42; linolcnic acid, iodine value 274-1; and tlup<inodomc acid, iodine value 367-7. Oleic acid occurs in all non-drying oils and fats, and to some extent in the semi-drying oiU and fats. Linolic acid is a characteristic constituent of all semi-drying, and to some extent of all drying oils. Linolcnic acid characterizes all vegetable drying oils; similarly clupanodonic acid characterizes all marine animal oils.
If one individual oil or fat is given, the iodine value alone furnishes the readiest means of finding its place in the above system, and in many cases of identifying it. Even if a mixture of several oils and fats be present, the iodine value assists c really in the identification of the components of the mixture, and furnishes the most important key for the attacking and resolving of (his not very simple problem. Thus it points the way to the application of a further method to resolve the isolated fatty acids of an oil or fat into saturated fatty acids, which do not absorb iodine, and into unsaturatcd fatty acids, which absorb iodine in various proportions as shown above. This separation is effected by converting the alkali soaps of the fatty acids into lead soaps and treating the latter with ether, in which the lead salts of the saturated acids are insoluble, whereas the salts of the above-named unsaturatcd acids are soluble. The saturated fatty acids can then be further examined, and valuable information is gained by the determination of the melting-points and by treatment with solvents. Thus some individual fatty acids, such as stcaric acid and arachidic acid (which is characteristic of ground nut oil) can be identified. In the mixture of unsaturatcd fatty acids, by means of some more refined methods, clupanodonic acid*, linolcnic acid, linolic acid and oleic acid can be recognized. By combining the various methods which have been outlined here, and by the help of some further additional special methods, and by reasoning in a strictly logical manner, it is possible to resolve a mixture of two oils and fats, and even of three and four, into their components and determine approximately their quantities. The methods sketched here do not yet exhaust the armoury of the analytical chemist, but it can only be pointed out in passing that the detection of hydroxylated acids enables the analyst to ascertain the presence of castor oil, just as the isolation and determination of ."'/,:.' fatty acids enables him to differentiate blown oils from other oils.
Tests such as the Maumene test, the claldin test and others, which formerly were the only resource of the chemist, have been practically superseded by the foregoing methods. The viscosity test, although of considerable importance in the examination of lubricating oils, has been shown to have very little discriminative value as a general test.
Commerce.—It may be safely said of the United Kingdom that it lakes the foremost position in the world as regards the extent of the oil and fat industries. An estimate made by the writer (Cantor Lectures, " Oils and Fats, their Uses and Applications," Society of Arts, 1004, p. 795), and based on the most reliable information obtainable, led to the conclusion that the sums involved in the oil and fai trade exceeded £1,000,000 per
week; in 1907 they approximated £1,950.000 per week. The great centres of the seed-oil trade (linseed, cotton-seed, rapeseed, castor-seed) are Hull, London, Liverpool, Bristol, Lciih and Glasgow. Linseed is imported principally from the East Indies, Argentina, Canada, Russia and the United States; cotton-seed is chiefly supplied by Egypt and East India; rape-seed and castor-seed chiefly by East India, The importation of copra and palm kernels for the production of coco-nut oil and palmnut oil is also considerable, but in these two cases Great Britain docs not take the first place. Fish and blubber oils arc principally produced in Dundee, London and Grecnock. The manufacture of cod-liver oil for pharmaceutical purposes is naturally somewhat limited, as Norway, Newfoundland, and latterly also Japan, arc more favourably situated as regards the supply of fresh cod, but the technical liver oils (cod oil, shark-liver oil) are produced in very large quantities in Grimsby, Hull, Aberdeen, and latterly also on the west coasts of the United Kingdom. The production of edible fats (margarine, lard compounds, and vegetable butters) has taken root in this country, and bids fair to extend largely. With regard to edible oils, edible cottonseed oil is the only table oil produced in Great Britain. The United Kingdom is also one of the largest importers of fatty materials.
Practically the whole trade in palm oil, which come* exclusively from West Africa, is confined to Liverpool, and the bulk of the tallow imported into Europe from Australasia, South America and the United Stales, is sold in the marts of London and Liverpool. Lard reaches Great Britain chiefly from the United States. Amongst the edible oils and fats which are largely imported, butter takes the first rank (to an amount of almost £25,000,000 per annum). This food-stuff reaches Great Britain not only from all butter-exporting countries of the continent of Europe, but in increasing quantities also from Australia, Canada, Argentine, Siberia and the United States of America. Next in importance is margarine, the British production of which docs not suffice for the consumption, so that large quantities must be imported from Holland, edible olive oil from Italy, the south of France, Spain and the Mediterranean ports generally. Coco-nut oil and copra, both for edible and technical purposes, are largely shipped to Great Britain from the East Indies and Ceylon, Java and the West Indies. Of lesser importance are greases, which form the by-product of the large slaughter-houses in the United States and Argentina, and American (Canadian) and Japanese fish oils.
On the continent of Europe the largest oil-trading centres are on the Mediterranean (Marseilles and Tricst), which are geographically more favourably placed than England for the production of such edible oils (in addition to the home-grown olive oil) as arachis oil,sesame oil and coco-nut oil. Moreover, the native population itself constitutes a large consumer of these oils. In the north of Europe, Hamburg, Rotterdam, Antwerp and Copenhagen are the largest centres of the oil and fat trade. Hamburg and its neighbourhood produces, curiously enough, at present the largest amount of palm-nut oil. The United States takes the foremost place in the world for the production of cottonseed and maize oils, lard, bone fat and Ash oils. Canada is likely to outstrip the United States in the trade of fish and blubber oils, and in the near future Japan bids fair to become a very serious competitor in the supply of these oils. Vast stores of hard vegetable fats are still practically wasted in tropical countries, such as India, Indo-China and the Sunda Islands, tropical South America, Africa and China. With the improvement in transport these will no doubt reach European manufacturing centres in larger quantities than has been ihe case hitherto.
The waxes consist chiefly of the fatty acid esters of the higher monohydric alcohols, with which are frequently associated free alcohols as also free fatty acids. In the following two tables the "-•! !• I. " and "alcohols" hitherto identified in waxes are enumerated in a classified order:—
Spermaceti consists practically of eery! palmitatc, Chinese wax of crryl palmitate. The other waxes are of more complex composition, tspeciilly so wool wax.
The waxes can be classified similarly to the oils and fats as
Mows;— I. Liouid waxe*
II. Sofid waxes.
A. Vegetable waxes.
B. Animal waxes.
Tie table enumerates the most important waxes:—
There are only iwo liquid waxes known, sperm oil and arctic fperm oil (boltlenose-whale oil), formerly always classed together with the animal oils. In their physical properties the natural i iimulile the (ally oils and fats. They behave similarly
to solvents; and in their liquid condition leave a grease spot on paper. An important property of waxes is that of easily forming emulsions with water, so that large quantities of water can be incorporated with them (lanolin).
The liquid waxes occur in the blubber of the sperm whale, and in the head cavities of those whalw which yield spermaceti; this latter is obtained by cooling the crude oil obtained from the head cavities. Vegetable waxes appear to be very widely distributed throughout the vegetable kingdom, and occur mostly as a very thin film covering leaves and also fruits. A few only are found in sufficiently large quantities to be of commercial importance. So far carnaliba wax is practically the only vegetable wax which isof importanccinthc world's markets. The animal waxes are widely distributed amongst the insects, the most important being beeswax, which is collected in almost all parts of the world. An exceptional position is occupied by wool wax, the main constituent of the natural wool fat which covers the hair of sheep, and is obtained as a by-product in scouring the raw wool. Wool fat is now being purified on a large scale and brought into commerce, under the name of lanolin, as an ointment the beneficent properties of which were known to Dioscorides in the beginning of the present era. Its chemical composition is exceedingly complex, and specially remarkable on account of the considerable proportions of cholesterol and isocholestcrol it contains.
Commerce.—The sperm oils arc generally sold in the same markets as the fish and blubber oils (see above). For beeswax London is one of the chief marts of the world. In Yorkshire, the centre of the woollen industry, the largest amounts of woolfat are produced, all'attempts to recover the hitherto wasted material in Argentine and Australia having so far not been attended with any marked success. Spermaceti is a comparatively unimportant article of commerce; and of Chinese wax small quantities only arc imported, as the home consumption takes up the bulk of the wax for the manufacture of candles, polishes and sizes.
2. Essential or Ethereal Oils.
The essential, ethereal, or "volatile " oils constitute a very extensive class of bodies, which possess, in a concentrated form, the odour characteristic of the plants or vegetable substances from which they are obtained. The oils are usually contained in special cells^ glands, cavities, or canals within the plants either as such or intermixed with resinous substances; in the latter case the mixtures form oleo-rcsins, balsams or resins according as the product is viscid, or solid and hard. A few do not exist ready formed in the plants, but result from chemical change of inodorous substances; as for instance, bitter almonds and essential oil of mustard.
The essential oils are for the most part insoluble or only very sparingly soluble in water, but in alcohol, ether, fatty oils and mineral oils they dissolve freely. They ignite with great case, emitting a smoke freely, owing to the large proportion of carbon they contain. Their chief physical distinction from the fatty oils is that they are as a rule not oleaginous to the touch and leave no permanent grease »pot. They have an aromatic smell and a hot burning taste, and can be distilled unchanged. The crude oils arc at the ordinary temperature mostly liquid, some are solid substances, others, again, deposit on standing a crystalline portion (" stcaroptcne * in contradistinction to the liquid portion (" elaeoptcne "). The essential oils possess a high refractive power, and most of them rotate the plane of the polarized light, fcven so nearly related oils as the oils of turpentine, if obtained from different sources, rotate the plane of the polarized light in opposite directions. In specific gravity the essential oils range from, 0-850 to 1-142; the majority arc, however, specifically lighter than water. In their chemical constitution the essential oils present no relationship to the fats and oils. They represent a large number of classes of substances of which the most important arc: (i) Hydrocarbons, such as pinenc in oil of turpentine, camphcne in citronclla oil, limoncne in lemon and orange-peel oils, caryophyllenc in clove oil and cumcne in oil of thyme; (2) kctonest such as camphor from the camphor tree, and ironc which occurs in orris root; (3) phenols, such as eugenot in clove oil, thymol in thyme oil, saffrol in sassafras oil, anethol in anise oil; (-i) aldehydes, such as citral and citronclhl, the most important constituents of lemon oil and lemon-grass oil, benzaldchydc in the oil of bitter almonds, cinnamic aldehyde in cassia oil, vanillin in gum benzoin and hcliotropin in the spiraea oil, &c.; (5) alcohols and their esters, such as geraniol (rhodinol) in rose oil and geranium oil, linalool. occurring in bergamol and lavender oils, ana as the acetic ester in rose oil, terpincol in cardamom oil, menthol in peppermint oil, cucalyptol in eucalyptus oil and borncpl in rosemary oil and Borneo camphor; (6) acids and their anhydrides, such as cinnamic acid in Peru balsam and coumarin in woodruff; and (7) nitrogenous compounds, such as mustard oil, indol in jasmine oil and anthranilic methyl-ester in neroli and jasmine oils.
Preparation from Plants.—Before essential oils could be prepared synthetically they were obtained from plants by one of the following methods: (i) distillation, (2) expression, (3) extraction, (4) cnfleuragc, (5) maceration.
The mo^t important of these processes is the first, as it is applicable to a large number of substances of the widest range, such as oil of peppermint and camphor. The process is based on the principle that whilst the odoriferous substances arc insoluble in water, their vapour tension is reduced on being treated with steam so that they arc carried over bv a current of steam. The distillation is generally performed in a still with an inlet for strain and an outlet to carry the vapours laden with essential oils into a condenser, where the water and oil vapours arc condensed. On standing, the distillate separates into two layers, an aqueous and an oily layer, the oil floating on or sinking through the water according to its specific
gravity. The process of expression is applicable to the obtaining of essential oils which arc contained in the rind or skin of the fruits belonging to the citron family, such as orange and lemon oils. The oranges, lemons, &c., arc peeled, and the peel is pressed against a large number of fine needles, the exuding oil being absorbed by sponges. It is intended to introduce machinery to replace manual labour. The process of extraction with volatile solvents is similar to that used in the extraction of oils and fats, but as only the most highly purified solvents can be used, this process has not yet gained commercial importance. The process of enftcuragc is used in those cases where the odoriferous substance is present to a very small extent, and is so tender and liable to deterioration that it cannot be separated by way of distillation. Thus in the case of ncroli oil the petals of orange blossom are loosely spread on trays covered with purified lard or with fine olive oil. The fatty materials then take up and fix the essential oil. This process is principally employed for preparing pomades and perfumed oils. Less tender plants can be treated by the analogous method of maceration, which consists in extracting the odoriferous substances by macerating the flowers in hot oilor molten fat. The essential oil is then dissolved by the fatty substances. The essential oil itself can be recovered from the perfumed oils, prepared either by cnHcurage or maceration, by agitating the perfumed fat in a shaking machine with pure concentrated alcohol. The essential oil passes into the alcoholic solution, which is used as such in perfumery.
Synthetic Preparation.—Since the chemistry of the essential oils has been investigated in a systematic fashion a large number of the chemical individuals mentioned above have been isolated from the oils and identified.
This first step lias led to the synthetical production of the most characteristic substances of essential oils in the laboratory, and the synthetical manufacture of essential oils bade fair to rival in importance the production of tar colours from the hydrocarbons obtained on distilling coat. One of the earliest triumphs of synthetical chemistry in this direction was the production of tcrpineol, the artificial lilac scent, from oil of turpentine. At present it is almost a by-product in the manufacture of artificial camphor. This was followed by the production of hcliotropin, coumarin and vanillin, and later on by the artificial preparation of iononc, the most characteristic constituent of the violet scent. At present the manufacture of artificial camphor may be considered a solved problem, although it is doubtful whether such camphor will be able to compete in price with the natural product in the future. The aim of the chemist to produce essential oils on a manufacturing scale is naturally confined at present to the more expensive oils. For so long as the great bulk of oils is so cheaply produced in nature's laboratory, the natural products will hold their field for a long time to come.
Applications.—Essential oils have an extensive range of uses, of which the principal arc their various applications in perfumery (q.v.). Next to that they play an important part in connexion with food. The value of flavouring herbs, condiments and spices is due in a large measure to the essential oils contained in them. The commercial value of tea, coffee, wine and other beverages may be said to depend largely on the delicate aroma which they owe to the presence of minute quantities of ethereal oils. Hence, essential oils are extensively used for the flavouring of liqueurs, aerated beverages and other drinks. Nor is their employment less considerable in the manufacture of confectionery and in the preparation of many dietetic articles. Most fruit essences now employed in confectionery arc artificially prepared oils, especially is this the case with cheap confectionery (jams, marmalades, &c.) in which the artificial fruit esters to a large extent replace the natural fruity flavour. Thus amyl acetate is used as an imitation of the jargonelle-pear flavour; amyl valcrale replaces apple flavour, and a mixture of ethyl and propyl butyratcs yields the so-called pine-apple flavour. Formic ether gives a peach-like odour, and is used for flavouring fictitious rum. Many of the essential oils find extensive use in medicine. In the arts, oil of turpentine is used on the largest scale in the manufacture of varnishes, and in smaller quantities for the production of tcrpincol and of artificial camphor. Oil of cloves is used in the silvering of mirror glasses. Oils of lavender and of spike are used as vehicles for painting, more especially lor the painting of pottery and glass.
The examination of essential oils is by no means an easy task. Each oil requires almost a special method, but with the progress of chemistry the extensive adulteration that used to be practised with fatty oils has almost disappeared, as the presence of fatty oils is readily detected. Adulteration of expensive oil with cheaper oils is now more extensively practised, and such tests as the determination