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HISTORY OF THE VEGETABLE KINGDOM. 



it is usually obtained, is well known as the use- 

 ful medicine called cream of tartar. 



Benzoic acid. The benzoin of the shops is 

 a resinous exudation from styrax lensoe, a tree 

 which grows in the island of Sumatra. From 

 this substance benzoic acid is procured. As it 

 is met with in commerce, it is usually contam- 

 inated with some resinous and oily matters. 

 Wlien pure, benzoic acid has no smell; when 

 sublimed, it assumes the form of long flat pris- 

 matic needles, having a beautiful silvery lustre. 

 It is used in medicine more to give flavour to 

 other more active drugs than for any efficacy it 

 possesses of itself. 



Prussic acid. This acid is generally classed 

 among the animal acids, because it is obtained 

 in greatest abundance from animal substances. 

 But it has been proved to exist in vegetable sub- 

 stances also, and is procured by distilling laurel 

 leaves, or the kernels of the peach and cherry, 

 or bitter almonds. When pure it forms a colour- 

 less fluid, with an odour resembling that of the 

 peach blossom. It does not redden vegetable 

 blues, but it is characterised by its property of 

 forming a bluish-gi-een precipitate when it is 

 poured with a little alkali added to it into 

 solutions containing iron. It is a virulent poison. 

 From experiments on the vegetable acids, it ap- 

 pears that they all contain, as elements, carbon, 

 oxygen, and hydrogen, and that prussic acid 

 contains a portion of nitrogen. Gallic acid con- 

 tains more carbon than the other vegetable acids, 

 and oxalic acid more oxygen. 



Modem chemistry has detected a great many 

 more acids in vegetable substances, such as in 

 kino, cinnamon, camphor, &c. 



Oils. Vegetable bodies afford a great variety 

 of oily substances, differing considerably in their 

 properties. These oils have been divided into 

 fixed, solid, and volatile. Fixed oils are but 

 seldom found except in the seeds of plants, and 

 especially in the dicotyledonous class. Occa- 

 sionally they exist in the pulp of fleshy fi-uits, 

 as in that of the olive, which yields the mostabun- 

 dant and valuable species of all fixed oils. But 

 dicotyledonous seeds which contain oil, contain 

 also at the same time a quantity of mucilage 

 and fecula, and form, when braised in water, a 

 mild and milky fluid known by the name of 

 emulsion; on this account they are sometimes 

 denominated emulsive seeds. Some seeds readily 

 yield their oil by simple pressure, having been 

 previously reduced to a soft pulp by pounding 

 them in a mortar. Others require to be exposed 

 to the action of heat, which is applied to them 

 by means of pressure between warm plates of 

 tin, or of tlie vapour of boDing water, or of 

 roasting before they are subjected to the press. 

 But the oil which is thus expressed, is still 

 mixed or combined with other substances, such 

 M fecula, starch, and mucilage, which sometimes 



subside spontaneously, if the liquid is kept in a 

 state of repose; first the grosser pai'ts, such as the 

 fragments of parenchyma, J.liat may have been ex- 

 pressed along with the oil; then the green fecula, 

 then the starch, and lastly the mucilage. The 

 oil is now left in a state of tolerable purity, 

 but not yet without a mixture of other sub- 

 stances, to deprive it of which chemists employ 

 a variety of processes. Fixed oil, when pure, 

 is generally a thick and viscous fluid, of a mild 

 or insipid taste, and without smell. But it is 

 never entirely without some coloui", which is 

 for the most part green or yellow. Its specific 

 gravity is to water as 9.403 to 1.000. It is insol- 

 uble in water, is decomposed by the acids, and 

 with the alkalies it forms soap. When exposed 

 to the atmosphere it becomes inspissated and 

 opaque, and assumes a white colour and a resem- 

 blance to fat. This is in consequence of the ab- 

 sorption of oxygen; but owing to the appear- 

 ance of a quantity of water in oU that is ex- 

 posed to the action of the air, it has been thought 

 that the oxygen absorbed by it is not yet perhaps 

 assimilated to its substance. When exposed to 

 cold it congeals and crystallizes, or assumes a 

 solid and granular form; but not till the ther- 

 mometer has, indicated a degree considerably 

 below the freezing point. When exposed to the 

 action of heat it is not volatilized till it begins 

 to boil, which is at 600° of Fahrenheit. By 

 distillation it is converted into water, carbonic 

 acid, and carburetted hydrogen and carbon; the 

 product of its combustion is nearly the sarae> 

 and hence it is a compound of carbon, oxygen, 

 and hydrogen. Some oils remain solid at the 

 ordinary temperature of the atmosphere, such 

 as palm and cocoa-nut oil, and wax, which in 

 its properties resembles the oleaginous bodies. 

 Of the fixed oils some are of a fatty nature, and 

 are readily inspissated by the action of the air; 

 others dry into a sort of tenacious varnish. 



Olive oil is expressed from the pulp of the 

 fruit of the olive tree, {Olea Europea) a shrub 

 that is indigenous to the south of Europe. In 

 the manufacture of the oil, the fruit is first broken 

 in a mill and reduced to a sort of paste. It is 

 then subjected to the action of a press, and tlie 

 oil, which is now easily separated, swims on the 

 top of the water in the vessel beneath. It is 

 manufactured chiefly in France and Italy, and 

 is much used throughout Europe to give a sea- 

 soning to food. 



Almond oil is extracted from the fruit of the 

 almond tree, (amygdalus communis) a native of 

 the south of Europe. The almonds are first 

 well rubbed or shaken in a coarse bag or sack, 

 to separate a bitter powder which covers their 

 epidermis. They are then pounded to a paste 

 in mortars of marble, which paste is afterwards 

 subjected to the action of a press, and the oil is 

 now obtained as in the case of the olive. It is 



