MANNA.

Manna; F. Manne; G. Manna.

Botanical Origin—Fraxinus Ornus L. (Ornus europæa Pers.), the Manna-ash, is a small tree found in Italy, whence it extends northwards as far as the Canton of Tessin in Switzerland and the Southern Tyrol. It also occurs in Hungary (Buda) and the eastern coasts of the Adriatic, in Greece, Turkey (Constantinople), in Asia Minor about Smyrna and at Adalia on the south coast. It grows in the islands of Sicily, Sardinia and Corsica, and is found in Spain at Moxente in Valencia.[1502] As an ornamental tree it has been introduced into Central Europe, where it is often seen of greater dimensions, sometimes acquiring a height of about 30 feet. It blossoms in early summer, producing numerous feathery panicles of dull white flowers which give it a pleasing appearance. The foliage exhibits great variation in shape of leaflets, even where the tree is uncultivated; and the fruits also are very diverse in form.

In some districts of Sicily, a little manna is obtained from the Common Ash, F. excelsior L.

History—The name Manna, though originally applied to the aliment miraculously provided for the sustenance of the ancient Israelites during their journey to the Holy Land, has been used to designate other substances of distinct nature and origin. Of these, the best known and most important is the saccharine exudation of Fraxinus Ornus L., which constitutes the Manna of European medicine.

It appears evident[1503] that previous to the 15th century, the manna in Europe was imported from the East and was not that of the ash. Raffaele Maffei, called also Volaterranus, a writer who flourished in the second half of the 15th century, states that manna began to be gathered in Calabria in his time, but that it was inferior to the oriental.[1504] At this period the manna collected was that which exuded spontaneously from the leaves of the tree, and was termed Manna di foglia or Manna di fronda: that which flowed from the stem bore the name of Manna di corpo and was less esteemed. All such manna was very dear.

About the middle of the 16th century, the plan of making incisions in the trunk and branches was resorted to, and although it was strenuously opposed even by legislative enactment, the more copious supplies which it enabled the collectors to obtain led it to being generally adopted. The Ricettario Fiorentino of the year 1573[1505] states that the manna “fatta con arte,” i.e. obtained by incisions, came from Cosenza in Calabria and differed not little from Syrian “manna mastichina.”[1506]

Manna di foglia became in fact utterly unknown, so that Cirillo of Naples, writing in 1770, expresses doubt whether it ever had any existence.[1507]

With regard to the history of manna-production in Sicily, there is this curious fact, that near Cefalù there exists an eminence in the Madonia range, called Gebelman or Gibelmanna, which in Arabic signifies manna-mountain. This name is not of modern origin, but is found in a diploma of the year 1082, concerning the foundation of the bishopric of Messina; and it has been held to indicate that manna was there collected during the Saracenic occupation of Sicily, a.d. 827 to 1070. We have not been successful in finding any evidence whether this supposition is well founded. On the other hand, it is remarkable that no writer, so far as we know, mentions manna as a production of Sicily, before Paolo Boccone of Palermo, who, after naming many localities for the drug in continental Italy, states that it is also obtained in Sicily.[1508]

Manna was also produced until recently in the Tuscan Maremma, but neither from that locality, nor from the States of the Church, where it was collected in the time of Boccone, is any supply now brought into commerce, though the name of Tolfa, a town near Civita Vecchia, is still used to designate an inferior sort of the drug.

The collection of manna in Calabria, which was imported up to the end of last century, has now almost entirely ceased.[1509]

Production—The manna of commerce is collected at the present day exclusively in Sicily. The principal localities producing the drug are the districts around Capaci, Carini, Cinisi, and Favarota, small towns 20 to 25 miles west of Palermo near the shores of the bay of Castellamare; also the townships of Geraci, Castelbuono, and other places in the district of Cefalù, 50 to 70 miles eastward of Palermo.

The manna-ash, in the districts whence the best manna is obtained, does not at the present day form natural woods, but is cultivated in regular plantations called frassinetti. The trees, which attain a height of from 10 to 20 feet, are planted in rows and stand about 7 feet apart, the soil between being at times loosened, kept free from weeds, and enriched by manure. After a tree is 8 years old and when its stem is at least 3 inches in thickness, the gathering of manna may begin; and may continue for 10 or 12 years, when the stem is usually cut down, and a young one brought up from the same root takes its place. The same stump thus has often two or three stems rising from it.

To obtain manna, transverse cuts from 1½ to 2 inches long and 1 inch apart, are made in the bark, just reaching to the wood. One cut is made daily, beginning at the bottom of the tree, the second directly above the first, and so on while dry weather lasts. In the following year, cuts are made in the untouched part of the stem, and in the same way in succeeding seasons. When after some years the tree has been cut all round and is exhausted, it is felled. Pieces of sticks or straws are inserted in the incisions, and become encrusted with the very superior manna, called Manna a cannolo, which however is unknown in commerce as a special sort. The fine manna ordinarily seen appears to have hardened on the stem of the tree. The manna which flows from the lower incisions, and is often collected on tiles or on a cup-shaped piece of the stem of the prickly pear (Opuntia), is less crystalline, and more gummy and glutinous, and is regarded of inferior quality.

The best time for notching the stems is in July and August, when the trees have ceased to push forth more leaves. Dry and warm weather is essential for a good harvest. The manna after removal from the tree, is laid upon shelves in order that it may dry and harden before it is packed. The masses left adhering to the stem after the finer pieces have been gathered, are scraped off and form part of the Small Manna of commerce.[1510]

Secretion—We have examined microscopically the bark of stems of Fraxinus Ornus that had been incised for manna at Capaci. It exhibits no peculiarity explaining the formation of manna, or any evidence that the saccharine exudation is due to an alteration of the cell-walls as in the case of tragacanth. The bark is poor in tannic matter; it contains starch, and imparts to water a splendid fluorescence due to the presence of Fraxin.

Description—Various terms have been used by pharmacological writers to designate the different qualities of manna, but in English commerce they are not now employed; and the better kinds of the drug are called simply Flake Manna, while the smaller pieces, usually loosely agglutinated and sold separately, are termed Small Manna or Tolfa Manna.

Owing to the gradual exudation of the juice and the deposition of one layer over another, manna has a stalactitic aspect. The finest pieces are mostly in the form of three-edged sticks, sometimes as much as 6 to 8 inches long and an inch or more wide, grooved on the inner side, which is generally soiled by contact with the bark; of a porous, crystalline, friable structure and of a pale brownish yellow tint, becoming nearly pure white in those parts which have been most distant from the bark of the tree. The pieces which are of deeper colour, and of an unctuous or gummy appearance, are less esteemed. Good manna is crisp and brittle, and melts in the mouth with an agreeable, honey-like sweetness, not entirely devoid of traces of bitterness and acridity. Its odour may be compared to that of honey or moist sugar.

Manna of the best quality dissolves at ordinary temperatures in about six parts of water, forming a clear, neutral liquid. It contains besides mannite, a small proportion of sugar and gum.

The manna which exudes from the older stems and from the lower parts of even young trees, contains more or less considerable quantities of gum and fermentable sugar, as well as extraneous impurities. The less favourable weather of the later summer and autumn promotes an alteration in the composition of the juice, and impairs its property of concreting into a crystalline mass.

Chemical Composition—The predominant constituent of manna, at least of the better sorts, is Manna-sugar or Mannite, C₆H₈(OH)₆ which likewise occurs, though in much smaller quantity, in many other plants besides Fraxinus. Artificially, it is produced by treating glucose, C₆H₁₂O₆, with sodium amalgam, and indirectly in the fermentation of glucose or of cane-sugar. It is isomeric with dulcite or melampyrin; crystallizes in shining prisms or tables, belonging to the rhombic system; melts at 166° C., and in very small quantity may by careful heating be sublimed and decomposed. It dissolves in 6·5 parts of water at 16° C., less freely in aqueous alcohol, very sparingly in absolute alcohol, and not in ether. The solution has an extremely weak rotatory power, and is not altered by boiling with dilute acids or alkalis, or with alkaline cupric tartrate.

Berthelot has shown that mannite is susceptible of fermentation, though not so easily as sugars belonging to the group of carbo-hydrates. The quantity of mannite in the best manna varies from 70 to 80 per cent.

When a solution of manna is mixed with alkaline cupric tartrate, rapid reduction to cuprous hydrate takes place even in the cold. This effect is due to the presence of a sugar which, according to Backhaus (1860), consists of ordinary dextro-glucose. It may amount to as much as 16 per cent., and is found in the best flake manna, but most abundantly in the unctuous varieties. Buignet[1511] has pointed out that the rotatory power of this sugar being inconsiderable, it probably consists of a mixture of Cane-sugar and Levulose. He found however that an aqueous solution of manna deviates powerfully to the right, a fact which he considers due to the presence of a large proportion of Dextrin. The best kinds of manna, according to Buignet, contain about 20 per cent. of dextrin; the inferior much more.

In our experiments we have not succeeded in isolating either dextrin or cane-sugar. There is present, even in the finest manna, a small amount of a dextrogyre mucilage, which is precipitated by neutral acetate of lead, and yields mucic acid when boiled with concentrated nitric acid.

Ether extracts from an aqueous solution of manna a very small quantity of red-brown resin, having an offensive odour and sub-acrid taste; together with traces of an acid which reduces silver salts and appears to be easily resinified. The quantity of water in the inferior kinds of manna often amounts to 10 or 15 per cent. The finest manna affords about 3·6 per cent. of ash.

The greenish colour of certain pieces of manna was formerly attributed to the presence of copper, till Gmelin, on account of the fluorescence of the solution, ascribed it to Æsculin. It is in reality produced by a body much resembling æsculin, namely Fraxin, C₁₆H₁₈O₁₀, occurring in the bark of the manna-ash and of the common ash, and together with æsculin, in that of the horse-chestnut. Fraxin crystallizes in colourless prisms, easily soluble in hot water and in alcohol, and having a faintly astringent and bitter taste. By dilute acids, it is resolved into Fraxetin, C₁₀H₈O₃, and Glucose, C₆H₁₂O₆. The presence of fraxin in manna, especially in the inferior sorts, is made apparent by the faint fluorescence of the alcoholic manna solution. The smallest fragment of the bark of the ash or the manna-ash immersed in water displays the same fluorescence.

Commerce—The exports of manna from Sicily[1512] (chiefly from Palermo) have been as follows:—

About half the quantity is sent to France. Italian commercial statistics[1513] represent the export of manna in 1870 thus:—in canelli 58,691 kilo. (1155 cwt.), in sorte 186,664 kilo. (3676 cwt.). The United Kingdom imported in the year 1870, 230 cwt. of manna, valued at £4447.[1514]

In 1877 the exports of “canelli” from Messina were 4273 kilogrammes, and of the drug “in sorte” 52,874 kilogr.; total value, 127,145 lire.

Adulteration—It can hardly be said that manna is subject to adulteration, though attempts to introduce a spurious manna made of glucose have been recorded. But considerable skill and ingenuity have been expended in converting the inferior sorts of manna into what has the aspect of fine natural Flake Manna, the manufacturers admitting however the factitiousness of their product. The artificial Flake Manna has the closest superficial resemblance to very fine pieces of the natural drug, but differs in its more uniform colour, and in being uncontaminated with the slight impurities, from which natural manna is never wholly free. It differs also in that when broken, no crystals of mannite are to be seen in the interstices of the pieces, and it wants the peculiar odour and slightly bitter flavour of natural manna. If one part of it is boiled with four of alcohol (0·838), a viscid honey-like residue will be obtained, whereas natural manna leaves undissolved a hard substance. Histed[1515] found it to afford about 40 per cent. of mannite, while fine manna similarly treated yielded 70 per cent.

Uses—A gentle laxative, much less frequently employed in this country than formerly, but still largely consumed in South America. Mannite, which possesses similar properties, is often prescribed in Italy.

Other sorts of Manna.

Various plants besides Fraxinus afford, under certain conditions, saccharine exudations, some of which constituted the Oriental Manna used in Europe in early times. So far as is known, they differ from officinal manna in containing no mannite.

Alhagi Manna; Turanjabín (Arabic); is afforded by Alhagi Camelorum Fisch. (Hedysarum Alhagi Pallas, non L.), a small spiny plant of the order Leguminosæ found in Persia, Afghanistan and Beluchistan. It had already been noticed by Isztachri.[1516] Excellent specimens of the manna, kindly obtained for us in the north-west of India by Dr. E. Burton Brown and Mr. T. W. H. Tolbort, show it as a substance in little roundish, hard, dry tears, varying from the size of a mustard seed to that of a hemp seed, of a light brown colour, agreeable saccharine taste, and senna-like smell. The leaflets, spines and pods of the plant, mixed with the grains of this manna, are characteristic and easily recognizable.

Villiers (1877) showed this manna to contain cane-sugar, a dextrogyrate glucose, and melezitose (see further on: Briançon manna, page 416). Ludwig[1517] had also found some dextrin and mucilage.

Alhagi Manna is collected near Kandahar and Herat, where it is found on the plants at the time of flowering. It is imported into India from Kabul and Kandahar to the extent of about 25 maunds (2000 lb.) annually; its value is reckoned at 30 rupees per secr, = 30s. per lb.[1518]

Gaz-anjabin (Arabic); Tamarisk Manna (in part)—In the months of June and July, the shrubs of tamarisk (Tamarix gallica var. mannifera Ehrenb.) growing in the valleys of the peninsula of Sinai, especially in the Wady es Sheikh, exude from their slender branches, in consequence of the puncture of an insect (Coccus manniparus Ehrenb.) little honey-like drops, which in the coolness of early morning are found in a solid state. This substance is Tamarisk Manna: it is collected by the Arabs, and by them sold to the monks of St. Katharine, who dispose of it to the pilgrims visiting the convent. Tamarisk Manna is also produced (but is perhaps no longer collected?) in Persia, where it is called Gaz-angabín;[1519] and probably likewise in the Punjab,[1520] from which regions it may have been brought to Europe in ancient times.

A specimen of tamarisk manna brought from Sinai, examined in 1861 by Berthelot, had the appearance of a thick yellowish syrup, contaminated with vegetable remains. It was found to consist of cane-sugar, inverted sugar (lævulose and glucose), dextrin and water, the last constituting one-fifth of the whole.[1521]

Although the name Gaz-angabín signifies tamarisk-honey, it is used according to Haussknecht[1522] at the present time in Persia, to designate certain round cakes, common in all the bazaars, of which the chief constituent is a manna collected in the mountain districts of Chahar-Mahal and Faraidan, and especially about the town of Khonsar, south-west of Ispahan, from Astragalus florulentus Boiss. et Haussk. and A. adscendens Boiss. et Haussk. The best sorts of this manna, which are termed Gaz Alefi or Gaz Khonsari, are obtained in August by shaking it from the branches, the little drops finally sticking together and forming a dirty, greyish-white, tough mass. The commoner sort got by scraping the stem, is still more impure. The specimen of it brought by Haussknecht yielded to Ludwig[1523] dextrin, uncrystallizable sugar and organic acids.

Shir-khist—Ancient writers on materia medica as Garcia d’Orta (1563) mention a sort of manna known by this name. The substance is still found in the bazaars of North-western India, being imported in small quantity from Afghanistan and Turkistan.[1524] Haussknecht in his paper on Oriental Manna already quoted, states that it is the exudation of Cotoneaster nummularia Fisch. et Mey. (Rosaceæ), also of Atraphaxis spinosa L. (Polygonaceæ), and that it is brought chiefly from Herat. We have to thank Dr. E. Burton Brown of Lahore, and Mr. Tolbort for specimens of this manna, which, from fragments it contains, is without doubt derived from a Cotoneaster. It is in irregular roundish tears, from about ¼ up to ¾ of an inch in greatest length, of an opaque dull white, slightly clammy, and easily kneaded in the fingers. It has a manna-like smell, a pure sweet taste and crystalline fracture. With water, it forms a syrupy solution with an abundant residue of starch granules.

Shír-khist was found by Ludwig to consist of an exudation analogous to tragacanth, but containing at the same time two kinds of gum, an amorphous levogyre sugar, besides starch and cellulose.

Oak Manna—The occurrence of a saccharine substance on the oak is noticed by both Ovid and Virgil, and it is also mentioned by the Arabian physicians, as Ibn Baytar[1525] and Elluchasem Elimithar.[1526] The last named, who died a.d. 1052, states that the exudation appears upon the oaks in the region of Diarbekir. At the present day, it is the object of some industry among the wandering tribes of Kurdistan, who, according to Haussknecht, collect it from Quercus Vallonea Kotschy and Q. persica Jaub. et Spach. These trees are visited in the month of August by immense numbers of a small white Coccus, from the puncture of which a saccharine fluid exudes, and solidifies in little grains. The people go out before sunrise, and shake the grains of manna from the branches on to linen cloths, spread out beneath the trees. The exudation is also collected by dipping the small branches on which it is formed, into vessels of hot water, and evaporating the saccharine solution to a syrupy consistence, which in this state is used for sweetening food, or is mixed with flour to form a sort of cake.

A fine specimen of the Oak Manna of Diarbekir was sent to the London International Exhibition of 1862. It constituted a moist soft mass of agglutinated tears, much resembling an inferior sort of ash-manna, and had an agreeable saccharine taste.

A less pure form of this manna occurs as a compact, greyish, saccharine mass, sometimes hard enough to be broken with a hammer. It consists of sugary matter, mixed with abundance of small fragments of green leaves, and has a herby smell and pleasant sweet taste. A sample of it brought from Diarbekir, examined by one of us, yielded 90 per cent. of dextrogyre sugar, which could not be obtained in a crystalline state, though it exists in such condition in the crude drug. Starch and dextrine were entirely wanting.[1527]

A specimen furnished to Ludwig[1528] by Haussknecht afforded much mucilage, a small amount of starch, about 48 per cent. of dextrogyre grape sugar, with traces of tannic acid and chlorophyll.

Briançon Manna—This is a white saccharine substance which, in the height of summer and in the early part of the day, is found adhering in some abundance to the leaves of the larch (Pinus Larix L.), growing on the mountains about Briançon in Dauphiny. It was formerly collected for use in medicine, but only to a very limited extent, for it was rare in Paris in the time of Geoffroy (1709-1731), and at the present day has quite disappeared from trade, though still gathered by the peasants. A specimen collected for one of us near Briançon in 1854, consists of small, detached, opaque, white tears, many of them oblong and channelled, and encrusting the needle-like leaf of the larch; they have a sweet taste and slight odour.[1529] Under the microscope they exhibit indistinct crystals.

Briançon manna has been examined in 1858 by Berthelot, who detected in it a peculiar sugar termed Melezitose, answering to the formula C₁₂H₂₂O₁₁ + OH₂.

Several other saccharine exudations have been observed by travellers and naturalists; we shall simply enumerate the more remarkable, referring the reader for further information to the original notices.

Pirus glabra Boiss. affords in Luristan a substance which, according to Haussknecht, is collected by the inhabitants, and is extremely like Oak Manna. It is stated by the same traveller that Salix fragilis L., and Scrophularia frigida Boiss., likewise yield in Persia saccharine exudations. A kind of manna was anciently collected from the cedar, Pinus Cedrus L.[1530] Manna is yielded in Spain by Cistus ladaniferus L.[1531] Australian Manna, which is in small rounded, opaque, white, dry masses, is found on the leaves of Eucalyptus viminalis Labill. It contains a kind of sugar called Melitose,[1532] has a sweet thistle, is devoid of medicinal properties and is not collected for use.[1533]

The substance named Tigala (corrupted into Trehala), from which a peculiar sugar has been obtained,[1534] is the coccoon of a beetle, and not properly a saccharine exudation.[1535]

The Lerp Manna of Australia is also of animal origin.[1536] It consists of water 14, white thread-like portion 33, sugar 53 parts. The threads possess some of the characteristic properties of starch, from which they differ entirely by their form and unalterability even in boiling water. Yet in sealed tubes, they dissolve in 30 parts of water at 135° C. The sugar is dextrogyre; it impregnates the threads as a soft brown amorphous mass. In the purified state it does not crystallize, even after a long time. By means of dilute sulphuric acid, the threads are converted into crystalline grape sugar.

OLEUM OLIVÆ.

Botanical Origin—Olea europæa L., an evergreen tree,[1537] seldom exceeding 40 feet in height, yet attaining extreme old age, abundantly cultivated in the countries bordering the Mediterranean, up to an elevation of about 2000 feet above the sea-level.[1538] Olea ferruginea Royle (O. cuspidata Wallich), a tree abundant in Afghanistan, Beluchistan and Western Sind, has been supposed to be a wild form of O. europæa, but is regarded by Brandis[1539] as a distinct species. It is not known to have been ever cultivated, yet its fruit, which is of a small size and but sparingly produced, is capable of affording a good oil.

History—In ancient Egypt the olive was known by the term bāk; it can be traced as far as the 17th century before our era.[1540]

According to the elaborate investigations of Ritter[1541] and of A. De Candolle,[1542] the olive tree is a native of Palestine, and perhaps of Asia Minor and Greece. Its original area also extends over north-eastern Africa; Schweinfurth[1543] regards it as undoubtedly wild on the mountains of Elbe and Soturba in lat. 22 N. on the western shores of the Red Sea, a locality which he visited in 1868. The olive tree has also been met with as far eastward as the country of the Gallas, where it is much appreciated as affording excellent timber.[1544] It is also stated by Theophrastus, that in his time the tree was plentiful in the Cyrenaica, the modern Barca, in northern Africa.

The olive would appear to have been introduced at a very remote period into north-western Africa and Spain. Willkomm (1876) is of the opinion that it was originally a native of the whole Mediterranean region.

At the present day it is largely cultivated in Algeria, Spain, Portugal, Southern France, Italy, the Greek Peninsula and Asia Minor. In the Crimea the tree grows well, but does not afford good fruit. It was carried to Lima in Peru about 1560 and still flourishes there, and in great plenty in the coast valleys further south as far as Santiago in Chili.[1545]

Olive oil is mentioned in the Bible so frequently that it must have been an important object with the ancient Hebrews. It held an equally prominent place among the Greeks and Romans,[1546] whose writers on agriculture and natural history treat of it in the most circumstantial manner. Olive fruits preserved in brine were used by the Romans as an article of food,[1547] and were an object of commerce with Northern Europe as early as the 8th century.[1548]

Production—In common with many important cultivated plants, the olive occurs under several varieties differing more or less from the wild form, the finer of which are propagated by grafting. It is also increased by the suckers which old trees throw up from their naked roots, and which are easily made to develope into separate plants.[1549] The fruit, an oval drupe, half an inch to an inch or more in length, and of a deep purple, is remarkable for the large amount of fat oil contained in its pulpy portion (sarcocarp). The latter is most rich in oil when ripe, containing then nearly 70 per cent., besides 25 per cent. of water. The unripe fruit, as well as other parts of the plant, abounds in mannite, which disappears in proportion as the oil increases. The ripe olive contains no mannite, it having probably been transformed into fatty oil.[1550]

The process for extracting olive oil varies slightly in different countries, but consists essentially in subjecting the crushed pulp of the ripe fruit to moderate pressure. The olives, which are gathered from the trees, or collected from the ground, in November, or during the whole winter and early spring, are crushed under a millstone to a pulpy mass. This is then put into coarse bags, which, piled upon one another, are subjected to moderate pressure in a screw press. The oil thus obtained is conducted into tubs or cisterns containing water, from the surface of which it is skimmed with ladles. This is called Virgin Oil. After it has ceased to flow, the contents of the bags are shovelled out, mixed with boiling water, and submitted to stronger pressure than before, by which a second quality of oil is got. If the fruit is left for a considerable time in heaps it undergoes decomposition, yielding by pressure a very inferior quality of oil called in French Huile fermentée. The worst oil of all, obtained from the residues, has the name of Huile tournante or Huile d’enfer.

It is said that in some districts the millstones are so mounted as to crush the pulp without breaking the olive-stones, and that thus the oil of the pulp is obtained unmixed with that of the kernels.[1551] We have made many inquiries in Italy and France as to this method of oil-making, but cannot find that it is anywhere followed.

The fixed oil of the kernels of ripe olives has been extracted and examined by one of us (F.). Though the kernels have a bitterish taste, the oil they yield is quite bland; by exposure to the vapour of hyponitric acid, it concretes like that of the pulp. If the whole of it were extracted in making olive oil, it would only be about as 1 part of oil of the kernel, to 40 parts of oil of the pulp.

Description—Olive Oil is a pale yellow or greenish yellow, somewhat viscid liquid, of a faint agreeable smell and of a bland oleaginous taste, leaving in the throat a slight sense of acridity.[1552] Its specific gravity on an average is 0·916 at 17° C. In cold weather, olive oil loses its transparency by the separation of a crystalline fatty body. The deposition takes place at a few degrees above the freezing point of water, and in some oils even at 10° C. (50° F.) If the oil is allowed to congeal perfectly, and is then submitted to strong pressure, about one-third of its weight of solid fat may be separated. After repeated crystallizations, this fat melts at 20 to 28° C. The fluid part or Olein, continues fluid at -4° to -10° C. Olive oil belongs to the class of the less alterable, non-drying oils.

The foregoing description does not apply to the inferior sorts of oil, which congeal more easily, are more or less deep-coloured, have a disagreeable odour and taste, and quickly turn rancid. These inferior oils have their special applications in the arts.

Chemical Composition--The chief constituent of olive oil is Olein or more correctly Triolein, C₃H₅(O·C₁₈H₃₃O)₃, identical so far as at present ascertained with the fluid part of all oils of the non-drying class. The proportion of olein in olive oil, as well as in other oils, is liable to variation, the result partly of natural circumstances and partly of the processes of manufacture. The best oils are rich in olein.

As to the solid part of olive oil, Chevreul believed it to be constituted of Margarin, which he first examined in 1820. But Heintz (1852 and later) showed margarin to be a mixture of palmitin with other compounds of glycerin and fatty acids. Collett in 1854 isolated Palmitic Acid, C₁₆H₃₂O₂, from olive oil; and Heintz and Krug (1857) further proved that Tripalmitin is the chief of the solid constituents of olive oil. They also met with an acid melting at 71°·4 C., which they regarded as Arachic Acid (p. 187). As to stearic acid, Heintz and Krug did not fully succeed in evidencing its presence in olive oil.

Lastly, Benecke discovered in olive oil a small quantity of Cholesterin, C₂₆H₄₄O. It may be removed by means of glacial acetic acid or alcohol, which dissolve but very little of the oil.

Commerce—Various sorts of olive oil are distinguished in the English market, as Florence, Gallipoli, Gioja, Spanish (Malaga and Seville), Sicily, Myteline, Corfu and Mogador.

Olive oil was imported into the United Kingdom in the year 1872 to the value of £1,193,064. Nearly half the quantity was shipped from Italy, one-fifth from Spain, and the remainder from other Mediterranean countries.

The average annual production in Italy is estimated at about 3 millions of hectolitres (66 million gallons), but the quantity exported does not reach half that amount.

The statistics of the French Government indicate the annual production of olive oil in France to be not more than 250,000 hectolitres, equivalent in value to 30 millions of francs (£1,200,000).[1553]

Uses—The uses of olive oil in medicine and its immense consumption in the warmer parts of Europe as an article of food, are too well known to require more than a passing allusion.

Adulteration—Olive Oil is the subject of various fraudulent admixtures with less costly oils, the means of detecting which has engaged much attention. Of the various methods by which chemists have endeavoured to ascertain the purity of olive oil, the following are the more noteworthy:—

a. Drying oils (such as the oils of poppy and walnut) may be distinguished by their not being converted into solid crystallizable elaidin by hyponitric acid or concentrated solution of nitrate of protoxide of mercury. Olive oil which contains any considerable proportion of one of these oils, no longer solidifies if exposed for a moment to one of the above-mentioned reagents. This test however is not of sufficient delicacy for small amounts of drying oils.

b. Olive oil being one of the lighter oils, the specific gravity may to some degree indicate admixture with a heavier oil. To make use of this fact, Gobley and other chemists have invented an instrument called an elaiometer, for taking the specific gravity of oils.

c. Observation of the Cohesion-figure.—This test, proposed by Tomlinson in 1864,[1554] depends on the forces of cohesion, adhesion, and diffusion. Thus, if a drop of any oil hanging from the end of a glass rod is gently deposited upon the surface of chemically clean water, contained in a clean glass, a contest takes place between the forces in question the moment the drop flattens down by its gravity upon the surface of the water. The adhesion of the liquid surface tends to spread out the drop into a film, the cohesive force of the particles of the drop strives to prevent that extension, and the resultant of these forces is a figure which Mr. Tomlinson believes to be definite for every independent liquid. The figure thus produced is named the cohesion-figure.

So far as our experience goes, the processes hitherto recommended for testing olive oil (and there are several that we have not mentioned) are only available in cases where the adulteration is considerable, and are quite insufficient for discovering a small admixture of other oils. How little they are appreciated, may be inferred from the fact that the Chamber of Commerce of Nice[1555] offered a reward of 15,000 francs (£600) for a simple and easy process for making evident an admixture with olive oil of 5 per cent. at least of any seed-oil.