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operates in the usual way The water circulation passes through the jacket by way of the pipes J and K. When the engine is running at heavy loads with full charges of oil delivered by the oil pump throcgh the sprayer G, a second pump is caused to come into action, which discharges a very small quantity of water through the water sj>n>tr valve F. This water passes into the vaporizer and combullion chamber, together with a little air, which enters by the automatic inlet valve, which serves as sprayer. This contrivance » found useful to prevent the vaporizer from overheating at heavy

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bads. The principal difference between this engine and the Hornsby engine already described lies in the use of the separate ignition tube H and in the water sprayer F, which acts as a snifting valve, taking in a little air and water when the engine becomes hot. Messrs Crossley inform the writer that the consumption of either crude or refined oil is about -63 of a pint per horse-power on full toad. They also give a test of a small engine developing 7 B.H.P., which consumed •601 pint per B.H.P. per hour of Roclc Light refined lamp oil and only •603 pint per B.H.P. per hour of crude Borneo petroleum oil.

Engines in which the oil is vaporized in a device external to the cylinder have almost disappeared, because of the great success of the Hornsby-Ackroyd type, where oil is injected into, and vaporized within, the cylinder. It has been found, however, that many petrol engines having jet carburettors will operate with the heavier oils if the jet carburet tor is suitably heated by means of the exhaust gases. In some engines it is customary to start with petrol, and then when the pans have become sufficiently heated to substitute paraffin or heavy petroleum oil, putting the heavy oil through the same spraying process as the petrol and evaporating the spray by hot walls before esterine the cylinder.

Mr Diesel has produced a very interesting engine which departs considerably from other types. In it air alone is drawn into the cylinder on the charging stroke; the air is compressed on the return stroke to a very high pressure generally to over 400 tb per sq. in. This compression raises the air to incandescence, and then heavy oil is injected into the incandescent air by a small portion of air compressed to a still higher point. The oil ignites at once as it enters the combustion space, and so a power impulse is obtained, but without explosion. The pressure does not rise above the pressure of air and oil injection. The Diesel engine thus emlxxlies two very original features; it operates at compression pressures very much higher than those used in any other internal combustion engines, and it dispenses with the usual igniting devices by rendering the air charge incandescent by compression. The engine operates generally on the Otto cycle, but it is also built giving an impulse at every revolution. Mr Diesel ha» shown great determination and perseverance, and the engine has now attained a position of considerable commercial importance. It is made on the continent, in England and in America in sizes up to 1000 H.P., and it has been applied to many purposes on land and also to the propulsion of small vessels. The engine gives a very high thermal efficiency. The present writer has calculated the following values from a test of a 500 B.H.P. Diesel oil engine made by Mr Michael Longridge, M.Inst.C.E. The engine had three cylinders, each of 22-05 m- diameter and stroke 39-52 in., each cylinder operating on the " Otto " cycle. The main results were as follows:—

Indicated power 595 horse

Brake power 459 „

Mechanical efficiency 77 %

Indicated thermal efficiency 41 %

Brake thermal efficiency ..... Ji'7%

(D. C)

OILLETS (from an O. Fr. diminutive of oil, eye, in Mod. Fr. toUtt; other English variants are oylets, eyelets, or eyelet-holes), the architectural term given to the arrow slits in the walls of medieval fortifications, but more strictly applied to the round

hole or circle with which the openings terminate. The same term is applied to the small circles inserted in the tracery-head of the windows of the Decorated and Perpendicular periods, sometimes varied with trefoils and quatrefoils.

OILS (adopted from the Fr. otic, mod. huilc, Lat. oleum, olive oil), the generic expression for substances belonging to extensive series of bodies of diverse chemical character, all of which have the common physical property of being fluid cither at the ordinary temperature or at temperatures below the boiling-point of water. Formerly, when substances were principally classified by obvious characteristics, the word included such a body as " oil of vitriol '* (sulphuric acid), which has of course nothing in common with what is now understood under the term oils. In its most comprehensive ordinary acceptation the word embraces at present the llui'l fixed oils or fatty oils (e.g. olive oil), the soft fats which may be fluid in their country of origin (e.g. coco-nut oil, palm oil), the hard fats (e.g. tallow), the still harder vegetable and animal waxes (e.g. carnatiba wax, beeswax), the odoriferous ethereal (essential) oils, and the fluid and solid volatile hydrocarbons—mineral hydrocarbons—found in nature or obtained from natural products by destructive distillation.

The common characteristic of all these substances is that they consist principally, in some cases exclusively, of carbon and hydrogen. They are all readily inflammable and are practically insoluble in water. The mineral hydrocarbons found in nature or obtained by destructive distillation do not ccme within the range of this article (see Naphtha, Paraffin, Petroleum), which is restricted to the following two large groups of bodies, formed naturally within the vegetable and animal organisms, viz. (i) Fixed oils, fats and waxes, and (2) Essential, ethereal or volatile oils.

i. Fixed Oils, Fats and Waxes,

The substances to be considered under this head divide themselves naturally into two large classes, viz, fatty (fixed) oils and fats on the one hand, and waxes on the other, the distinction between the two classes being based on a most important chemical difference. The fixed oils and fats consist essentially of glyceridcs, i.e. esters formed by the union of three molecules of fatty acids with one molecule of the trihydric alcohol glycerin (q.y.), whereas the waxes consist of esters formed by the union of one molecule of fatty acid with one molecule of a monohydric alcohol, such as cetyl alcohol, cholesterol, &c. Only in the case of the wax coccerin two molecules of fatty acids arc combined with one molecule of a dihydric (bivalent) alcohol. It must be pointed out that m common parlance this distinction does not find its ready expression. Thus Japan wax is a glyceride and should be more correctly termed Japan tallow, whereas sperm oil is, chemically speaking, a wax. Although these two classes of substances have a number of physical properties in common, they must be considered under separate heads. The true chemical constitution of oils and fats was first expounded by the classical researches of Chevreul, embodied in his work, Rcehcrchcs sur les corps gras d'origine animale (1823, reprinted 1889).

(a) Fatty (fixed) Oils and Fats.—The fatty (fixed) oils and fats form a well-defined and homogeneous group of substances, passing through all gradations of consistency, from oils which are fluid even below the freezing-point of water, up to the hardest fats which melt at about 50° C. Therefore, no sharp distinction can be made between fatty oils and fats. Nevertheless, it is convenient to apply the term " oil " to those glycerides which are fluid below about 20° C.t and the term " fat " to those which are solid above this temperature.

Chemical Composition.—No oil or fat is found in nature consisting of a single chemical individual, i.e. a fat consisting of the glyceride of one fatty acid only, such as stearin or tristearin, CaHs(O-C,sH36O)j, the glycerin ester of stearic acid, C^HwCOsH. The natural oils and fats are mixtures of at least two or three different triglyceridcs, the most important of which are tristearin, tripalmitin, C8Hi(O-C,0H3lO)3 and triolcin, C3H5 (OCigHuO)j. These three glycerides have been usually considered the chief

constituents of most oils and fats, but latterly there have been
recognized as widely distributed trilinolin, the glyceride of
linolic acid, and trilinolenin, the glyceride of linolenic acid.
The two last-named glycerides are characteristic of the semi-
drying and drying oils respectively. In addition to the fatty
acids mentioned already there occur also, although in much
smaller quantities, other fatty acids combined with glycerin, as
natural glycerides, such as the glyceride of butyric acid in butter-
fat, of caproic, caprylic and capric acids in butter-fat and in
coco-nut oil, lauric acid in coco-nut and palm-nut oils, and
myristic acid in mace butter. These glycerides are, therefore,
characteristic of the oils and fats named.
In the classified list below the most important fatty acids
occurring in oils and fats are enumerated (cf. Waxes, below).

Oils and fats must, therefore, not be looked upon as definite chemical individuals, but as representatives of natural species which vary, although within certain narrow limits, according to the climate and soil in which the plants which produce them are grown, or, in the case of animal fats, according to the climate, the race, the age of the animal, and especially the food, and also the idiosyncrasy of the individual animal. The oils and fats are distributed throughout the animal and vegetable kingdom from the lowest organism up to the most highly organized forms of animal and vegetable life, and are found in almost all tissues and organs. The vegetable oils and fats occur chiefly in the seeds, where they are stored to nourish the embryo, whereas in animals the oils and fats are enclosed mainly in the cellular tissues of the intestines and of the back.

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Up to recently the oils and fats were looked upon as consisting in the main of a mixture of triglycerides, in which the three combined fatty acids are identical, as is the case in the abovenamed glycerides. Such glycerides are termed “simple glycerides.” Recently, however, glycerides have been found in which the glycerin is combined with two and even three different acid radicals; examples of such glycerides are distearo-olein, C.Hs(O.Cisłłs:0), (O.CisBuO), and stearo-palmito-olein, C.H.(O.Cishs:0) (O.Cishino) (O.Cisha;0). Such glycerides are termed “mixed glycerides.” The glycerides occurring in natural oils and fats differ, therefore, in the first instance by the different fatty acids contained in them, and secondly, even if they do contain the same fatty acids, by different proportions of the several simple and mixed glycerides.

Since the methods of preparing the vegetable and animal fats are comparatively crude ones, they usually contain certain impurities of one kind or another, such as colouring and mucilaginous matter, remnants of vegetable and animal tissues, &c. For the most part these foreign substances can be removed by processes of refining, but even after this purification they still retain small quantities of foreign substances, such as traces of colouring matters, albuminoid and (or) resinous substances, and other foreign substances, which remain dissolved in the oils and fats, and can only be isolated after saponification of the fat. These foreign substances are comprised in the term “unsaponifiable matter.” The most important constituents of the “unsaponifiable matter” are phytosterol Co. HoO or Co. H.O(?), and the isomeric cholesterol. The former occurs in all oils and fats of vegetable

OILS

origin; the latter is characteristic of all oils and fats of animal origin. This important difference furnishes a method of distinguishing by chemical means vegetable oils and fats from animal oils and fats. This distinction will be made use of in the classification of the oils and fats. A second guiding principle is afforded by the different amounts of iodine (see Oil Testing bek>w) the various oils and fats are capable of absorbing. Since this capacity runs parallel with one of the best-known properties of oils and fats, viz. the power of absorbing larger or smaller quantities of oxygen on exposure to the air, we arrive at the following classification:—

I. Fatty Oils Or Liquid Fats
A. Vegetable oilt. B. Animal oils.

1. Drying oils. I. Marine animal oils.

2. Semi-drying oils. (a) Fish oils.

3. Non-drying oils. (b) Liver oils

(c) Blubber oils.
2. Terrestrial animal oils.

II. Solid Fats
A. VqetaUe fats. B. Animal fats.

1. Drying fats.

2. Semi-drying fats.

3. Non-drying fats.

Physical Properties.—The specific gravities of oils and fats varv between the limits of 0-910 and 0-975. The lowest specific gravity i» owned by the oils belonging to'thc rape oil group--from 0-913 to 0-916. The specific gravities of most non-drying oils lie between 0-916 and 0-920, and of most semi-drying oils between 0-920 and 0-925. whereas the drying oils have specific gravities of about 0-930. The animal and vegetable fats possess somewhat higher specific gravities, up to 0-930. The high specific gravity, 0-970, is owned by castor oil and cacao butter, and the highest specific gravity observed hitherto, 0-975. by Japan wax and myrtle wax.

In thei- liquid state oils and fats easily penetrate into the pores of dry substances; on paper they leave a translucent spot -grease spot "—which cannot be removed by washing with water and subsequent drying. A curious fact, which may be used for the detection of the minutest quantity of oils and fats, is that camphor crushed between layers of paper without having been touched with the fingers rotates when thrown on clean water, the rotation ceasing immediately when a trace of oil or fat is added such as introduced by touching the water with a needle which has been passed previously through the hair.

The oils and fats are practically insoluble in water. With the exception of castor oil they arc insoluble in cold alcohol; in boiling alcohol somewhat larger quantities dissolve. They are completely soluble in ether, carbon bisulphide, chloroform, carbon tetrachloride, petroleum ether, and benzene. Oils and fats have no distinct melting or solidifying point. This is not only due to the fact that they arc mixtures of several glycerides, but also that even pure glycerides, such as tristearin, exhibit two melting-points, a so-called "double melting-point," the triglycerides melting at a certain temperature, then solidifying at a higher temperature to melt again on further beating. This curious behaviour was looked upon by Duffy as being due to the existence of two isomeric modifications, the actual occurrence of which has been proved (1907) in the case of several mixed elycerides.

The freezing-points of those oils which are fluid at the ordinary temperature range from a few degrees above zero down to -28* C (linseed oil). At low temperatures solid portions—usually termed "stearine "—separate out from many oils; in the case of cotton-seed oil the separation takes place at 12° C. These solid portions can be filtered off, and thus are obtained the commercial " dcmargarinated cils " or " winter oils."

Oils and fats can be heated to a temperature of 200° to 250" C. without undergoing any material change, provided prolonged contact with air is avoided. On being heated above 250* up to 300° some oils, like linseed oil, safflower oil, tung oil (Chinese or Japanese •wood oil) and even castor oil, undergo a change which is most likely doe to polymerization. In the case of castor oil solid products are formed. Above 300** C. all oils and fats are decomposed; this is evidenced by the evolution of acrolein, which possesses the wellknown pungent odour of burning fat. At the same time hydrocarbons are formed (see Petroleum).

On exposure to the atmosphere, oils and fats gradually undergo certain changes. The drying oils absorb oxygen somewhat rapidly and dry to a film or skin, especially if exposed in a thin layer. Extensive use of this property is made in the paint and varnish trades. The semi-drying oils absorb oxygen more slowly than the drying oils, and are, therefore, useless as paint oils. Still, in course of time* they absorb oxygen distinctly enough to become thickened. The property of the semi-drying

oils to absorb oxygen is accelerated by spreading such oils over a large surface, notably over woollen or cotton fibres, when absorption proceeds so rapidly that frequently spontaneous combustion will ensue. Many tires in cotton and woollen mills have been caused thereby. The non-drying oils, the type of which is olive oil, do not become oxidized readily on exposure to the air, although gradually a change takes place, the oils thickening slightly and acquiring that peculiar disagreeable smell and acrid taste, which arc defined by the term " rancid." The changes conditioning rancidity, although not yet fully understood in all details, must be ascribed in the first instance to slow hydrolysis (" saponification ") of the oils and fats by the moisture of the air, especially if favoured by insolation, when water is taken up by the oils and fats, and free fatty acids are formed. The fatty acids so set free are then more readily attacked by the oxygen of the air, and oxygenated products are formed, which impart to the oils and fats the rancid smell and taste. The products of oxidation are not yet fully known; most likely they consist of lower fatty acids, such as formic and acetic acids, and perhaps also of aldehydes and ketones. If the fats and oils are well protected from air and light, they can be kept indefinitely. In fact C. Frit-del has found unchanged triglycerides in the fat which had been buried several thousand years ago in the tombs of Abydos. If the action of air and moisture is allowed free play, the hydrolysis of the oils and fats may become so complete that only the insoluble fatty acids remain behind, the glycerin being washed away. This is exemplified by adipocere, and also by Irish bog butter, which consist chiefly of free fatty acids.

The property of oils and fats of being readily hydrolysed is a most important one, and very extensive use of it is made in the arts (soapmaking, candle-making and recovery of their by-products). If oils and fats are treated with water alone under high pressure (corresponding to a temperature of about 220° C.), or in the presence of water with caustic alkalis or alkaline earths or basic metallic oxides (which bodies act as "catalysers ") at lower pressures, they are converted in the first instance into free fatty acids and glycerin. If an amount of the bases sufficient to combine subsequently with the fatty acids be present, then the corresponding salts of these fatty acids are formed, such as sodium salts of fatty acids (hard soap) or potassium salts of the fatty acids (soft soap), soaps of the alkaline earth (lime soap}, or soaps of the metallic oxides (zinc soap, &c.). The conversion of the glycerides (triglycerides) into fatty acids and glycerin must be looked upon as a reaction which takes place in stages, one molecule of a triglyceride being converted first into diglyceride and one molecule of fatty acid, the diglyceride then being changed into monoglyccride, and a second molecule of fatty acid, and finally the monoglyccride being converted into one molecule of fatty acid and glycerin. All these reactions take place concurrently, so that one molecule of a diglyceride may still retain its ephemeral existence, whilst another molecule is already broken up completely into free fatty acids and glycerin.

The oils and fats used in the industries are not drawn from any very great number of sources. The tables on the following pages contain chiefly the most important oils and fats together with their sources, yields and principal uses, arranged according to the above classification, and according to the magnitude of the iodine value. It should be added that many other oils and fats are only waiting improved conditions of transport to enter into successful competition with some of those that are already on the market.

Extraction.—Since the oils and fats have always served the human race as one of the most important articles of food, the oil and fat industry may well be considered to be as old as the human race itself. The methods of preparing oils and fats range themselves under three heads: (i) Extraction of oil by "rendering," i.e. boiling out with water; (2) Extraction of oil by expression; (3) Extraction of oil by means of solvents.

Rendering.—The crudest method of rendering oils from seeds, still practised in Central Africa, in Indo-China and on some of the South Sea Islands, consists in heaping up oleaginous fruits and allowing them to melt by the heat of the sun. when the exuding oil runs on and is cojlectea. In a somewhat improved form this process of rendering is practised in the preparation of palm oil, and the rendering the best (Cochin) coco-nut oil by boiling the fresh kernels with water. Since hardly any machinery, or only the simplest machinery, is required for these processes, this method has some fascination for inventors, and even at the present day processes are being patented, having for their object the boiling out of fruits with water or salt solutions, so as to facilitate the separation of the oil from the pulp by gravitation. Naturally these processes can only be applied to those seeds which contain large quantities of fatty matter, such as coconuts and olives. The rendering process is, however, applied on a very large scale to the production of animal oils and fats. Formerly the animal oils and fats were obtained by heating the tissues containing the oils or fats over a frc*i fire, when the cell membranes burst and the liouid fat flowed out. The cave-dweller who first collected the fat dripping off the deer on the roasting spit may well be lookod upon as the first manufacturer of tallow. This crude process is now classed amongst the noxious trades, owing to the offensive stench given off, and must be considered as almost extinct in this country. Even on whaling vessels, where up to recently

whale oil, seal oil and sperm oil (see Waxes, below) were obiained exclusively by " trying,' i.e. by melting the blubber over a free fire, the process of rendering is fast becoming obsolete, the modern practice being to deliver the blubber in as fresh a state as possible to the "whaling establishments," where the oil is rendered by methods clost-ly resembling those worked in the enormous rendering establishments (for tallow, lard, bone fat) in the United States and in South America. The method consists essentially in cutting up the fatty matter into small fragments, which are transferred into vessels containing water, wherein the comminuted mass is heated by steam, cither under ordinary pressure in open vessels or under higher pressure in d:gestors. The fat gradually exudes and collects on the top of the water, whilst the membranous matter, " greaves," falls to the bottom. The fat is then drawn off the aqueous (gluey) layer, and strained through sieves or filters. The greaves are placed in hair or woollen bags and submitted to hydraulic pressure, by which a further portion of oil or fat is obtained (cf Pressing, below). In the case of those animal fats which are intended for edible purposes, such as lard, suet for margarine, the greatest cleanliness must, of course, be observed, and the temperature must be kept as low as possible in order to obtain a perfectly sweet and pure material.

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Pressing.—The boiling out process cannot be applied to small «cds, such as linseed and rape seed. Whilst the original method of obtaining seed oils may perhaps have been the same which is still o»ed in India, viz. trituration of (rape) seeds in a mortar so that the oil can exude, it may be safely assumed that the process.of expressing has been applied in the first instance to the preparation of olive oil. The first woman who expressed olives packed in a sack by heaping stones on them may be considered as the forerunner of the inventor* cf all the presses that subsequently came into use. Pliny describes in detail the apparatus and processes for obtaining olive oil in vogue among his Roman contemporaries, who used already a simple screw press, a knowledge of which they had derived from the Greeks, fa the East, where vegetable oils form an important article of food and serve also for other domestic purposes, various ingenious applications of lever presses and wedge presses, and even of combined lever and wedge presses, have been used from the remotest time. At an early stage of history the Chinese employed the same •cries of operations which are followed in the most advanced oil mills of modern time, viz. bruising and reducing the seeds to meal under an edge-stone, heating the meal in an open pan, and pressing out the oil in a wedge press in which the wedges were driven home by hammers. This primitive process is still ocing carried out in Manchuria, in the production of soja bean cake and soja bean oil, one of the staple industries of that country. The olive press, which was also used in the vineyards for expressing the grape juice, found its way from the south of France to the north, and was employed there for expressing poppy seed and rape seed. The apparatus was then gradually improved, and thus were evolved the modern forms of fhe screw press, next the Dutch or stamper press, and finally the hydraul:c press. With the screw press, even in its most improved form, the amount of pressure practically obtainable is limited from the failure of it* parts under the severe inelastic strain. Hence this kind of press finds only limited application, as in the industry of olive oil for expressing the best and finest virgin oil, and in the production of animal fats for edible purposes, such as lard and oleomargarine. The Dutch or stamper press, invented in Holland in the ijth century, was up to the early years of the iQth century

almost exclusively employed in Europe for pressing oil-seeds. It consists of two principal parts, an oblong rectangular box with an arrangement of plates, blocks and wedges, and over it a framework with- neavy stampers which produce the pressure by their fall. The press box first consisted of strongly bound oaken planks, but later on cast-iron boxes were introduced. At each extremity of the box a bag of oil-meal was placed between two perforated iron plates, next to which were inserted filling-up pieces of wood, two of which were oblique, so that the wedges which exercised the pressure could be readily driven home. This press has had to yield place to the hydraulic press, although in some old-fashioned establishments in Holland the stamper press could still be seen at work in the 'eighties of the igth century. The invention of the hydraulic press in 1795

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almost unlimited source ol power into play; the limit ot the power being solely reached by the limit of the strength of the material which the engineer is able to produce. Since then the hydraulic press has practically completely superseded all other appliances used for expression, and in consequence of this epoch-making invention, assisted as it was later on by the accumulator—invented by William George (later Lord) Armstrong in 1843—the seed-crushing industry reached a perfection of mechanical detail which soon secured its supremacy for England.

The sequence of operations in treating oil seeds, oil nuts, &e., for the separation of their contained oils is at the present time as follows: As a preliminary operation the oil seeds and nuts are freed from dust, sand and other impurities by sifting in an inclined revolving cylinder or sieving machine, covered with woven wire, having meshes varying according to the size and nature of the seed operated upon. This preliminary purification is of the greatest importance, especially lor the preparation of edible oils and fats. In the case of those seeds amongst which are found pieces of iron (hammer heads amongst palm kernels, &c.), the seeds are passed over magnetic separators, which retain the pieces of iron. The seeds and nuts are then decorticated (where required), the shells removed, and the kernels (" meats ") converted into a pulpy mass or meal (in older establishments by crushing and grinding between stones in edge-runners) on passing through a hopper over rollers consisting of five chilled iron or steel cylinders mounted vertically like the bowls of a calendar. These rollers are finely grooved so that the seed is cut up whilst passing in succession between the first and second rollers in the scries, then between the second and the third, and so

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