220 SCIENCE OF AGRICULTURE. Part II. 



cordlngly denominated native adds ; together with the mucous, pyromucous, pyrotartarous, pyrollgnous, 

 camphoric, and suberic, which do not exist ready formed in the plant, and are hence denominated arti- 

 licial acids. They are consequently not within the scope of the object of the present work. 



1598. Oxalic add. If the expressed juice of the oxalis aceto. blues. It is soluble both in water and alcohol; andisdistln- 

 sella is left to evaporate slowly, it deposits small crystals of a guished by its property of communicating to solutions of iron 

 yellowish color and saltish taste, which are known by the a deep purple color. When exposed to a gentle heat it sub- 

 name of the acidulum of sorrel, that is, a salt with excess of limes without alteration, but a strong heat decomposes it. 

 acid, from which the acid may be obtained pure by processes Nitric acid converts it into the malic and oxalic acids. It is of 

 well known to the chemist. It is not used in medicine or treat utility in the art of dyeing, and forms the basis of ail 

 the 'arts, except in its state of acidulum, in which it is em- black colors, and of colors with a dark ground. It forms also 

 " to make a sort of lemonade, and to discharge stains of the basis of ink ; and chemists use it as a test to detect the 



El^il 



ink. It has been found also in oxalis corniculata, geranium presence of iron. 



acidum, in the several species of rumex, and in the pubescence 1403. Tartaric acid. If wine is kept for a length of time in a 



of cicer arietinum. cask or other close vessel, a sediment is precipitated which 



1399. Acetic acid. The acetic acid, or vinegar, which is ge- adheres to the sides or bottom, and forms a crust known by the 

 nerally manufactured from wine in a certain stage of ferment- name of tartar, which is a combination of potass and a pecu- 

 ation, has been found also ready formed in the sap of several liar acid in excess. The compound is tartarite of potass, and 

 trees, as analysed by Vauquelin ; and also in the acid juice the acid, in its state of purity, is the tartaric acid. It is cha- 

 of the cicer arietinum, of which it forms a constituent part. racterised by the property of its forming with potass a salt that 

 It was obtained also by Scheele from the sap of the sambucus is soluble with difficulty. It has been found in the following 

 nigra ; and is consequently to be regarded as a native vegetable vegetable substances also : in the pulp of tamarinds, in the 

 acid. It is distinguished from other vegetable acids by its juice of the grape, and mulberries, sorrel, and sumac, and 

 forming soluble salts with the alkalies and earths. the roots of triticum repens, and leontodon taraxacum. It is 



1400. C'i<rtc arirf. Citric acid is the|acid that exists in the juice not much used except among chemists. But the tartarite 

 of lemon. Its taste is very sour in a state of purity, but ex- from which it is usually obtained is well known for its medical 

 ceedingly pleasant when diluted with water. By a red heat it virtues under the name of cream of tarur. 



yields carbonic acid gas and carbonatedlhydrogene gas, and is 1404. Benzoic acid. Frooi the styrax benzoin there exudes a re- 

 reduced to a charcoal ; nitric acid converts it into oxalic and sinous substance, known in the shops by the name of benzoin, 

 acetic acid, and with lime it forms a salt insoluble in water. and in which the benzoic acid is contained. It is distinguished 

 It has been found unmixed with other acids in the following from the other acids by the aromatic odor and extreme volati- 

 vegetable substances : in the juice of oranges and lemons, and lity. It has been obtained also from the balsams of tolu and 

 in the berries of vaccinium oxycoccus, and vitis idsea, prunus storax ; and is used in pharmacy, in the preparation of boluses 

 padus, solanum dulcamara, and rosa canina. It has been found and electuaries, 

 also in many other fruits, mixed with other acids. 1405. Prussic acid. The prussic acid is generally classed 



1401. Malic acid. Malic acid is found chiefly inthe juice of among the animal acids, because it is obtained in the greatest 

 unripe ap{)les, whence it derives its name. But it is found also abundance from animal substances. But it has been proved 

 in the juice of barberries, alderberries, gooseberries, plums, to exist in vegetable substances also, and it is procured by dis- 

 and common house-leek. tilling laurel leaves, or the kernels of the peach and cherry, or 



1402. Gallic add. Gallic acid, as it is obtained in the greatest bitter.almonds. When pure it exists in the form of colorless 

 abundance, so it derives its name from the nut-gall, from fluid, with an odor resembling that of ])each.tree blossoms. It 

 which it may be extracted by exposing a quantity of the powder does not redden vegetable blues. But it is characterised by its 

 of nut-galls to a moderate heat m a glass retort ; and the acid property of forming a bluish -green precipitate, when it is 

 will sublime and form crystals of an octahedral figure. Its poured, with a little alkali added to it, into solutions containing 

 taste is austere and astringent. It strongly reddens vegetable iron. 



1406. All vegetable acids contain carbon, oxygen, and hydrogen, in one propwtion or other ; and the 

 prussic acid contains also a portion of nitrogen. The gallic acid contains more of carbon than any other 

 vegetable acid, and the oxalic more of oxygen. 



1407. Vegetable oils are of two kinds, the fixed and the volatile. The former are 

 not suddenly affected by the application of heat ; the latter are very inflammable, 



1408. Fixed oils. Fixed oils are but seldom found, except in the seeds of plants, and chiefly in such aa 

 are dicotyledonous. They are found also, though rarely, in the pulp of fleshy fruits, as in that of the olive, 

 which yields the most abundant 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 bruised in 

 water, a mild and milky fluid, known by the name of emulsion. And on this account they are sometimes 

 denominated emulsive seeds. Some seeds yield their oil merely by means of pressure, though it is often 

 necessary to reduce them first of all to a sort of pulp, by means of 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 the vapor of boiling water, or of roasting before they are subjected to the press. 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 color, which is for the most part green or yellow. Its specific gravity is to 

 water as 9-403 to 1000. It is insoluble in water. It is decomposed in the acids, but with the alkalies it 

 forms soap. When exposed to the atmosphere it becomes inspissated and opaque, and assumes a white 

 color and a resemblance to fat. This is in consequence of the absorption of oxygen ; but owing to the 

 appearance of a quantity of water in oil that is exposed 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 con- 

 geals and crystallizes, or assumes a solid and granular form ; but not till the thermometer 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 GOO'' of Fahrenheit. By distillation it is converted into water, carbonic acid, 

 and carburetted hydrogen gas, and charcoal ; the product of its combustion is nearly the same ; and hence 

 it is a compound of carbon, oxygen, and hydrogen. Fixed oils are generally divided into two sorts, fat 

 oils and drying oils. The former are readily inspissated by the action of the air, and converted into a sort 

 of fat. The latter are capable of being dried by the action of the air, and converted into a firm and trans- 

 parent substance. 



1409. The principal species of fat oils are the following : 



1410. Olive-oil, which is expressed from thepulpy part of the pounded to a paste in mortars of marble, which is afterwards 

 fruit of olea europea. The truit is first broken in a mill, and subjected to the action of the press ; and the oil is now ob- 

 reduced to a sort of paste. It is then subjected to the action of tained as in the olive. 



a press, and the oil, which is now easily separated, swims on the 1415!. Rapcseed-oil, which is extracted from the brassica napus 



top of the water in the vessel beneath. It is manufactured and campestris. It is less fixed and less liable to become ran- 



chiefly in France and in Italy, and is much used throughout cid than the two former, and is manufactured chiefly in 



Europe instead of butter, and to give a seasoning to food. Flanders. 



1411. Oi/(>fa/ron<;, which is extracted from the fruit of the 1413. Oil of behen, -which is extracted from the fruit of the 

 amygdalus communis or common almond. The almonds are guilandina mohringa, common in Egypt and Africa. It is apt 

 first well rubbed or shook in a coarse bag or sack, to separate a to become rancid ; but it is without odor, and is on tliis ac- 

 bitter powder which covers their epidermis. They are then count much used in perfumery. 



1414. The principal species of drying oils are linseed-oil, nut-oil, poppy-oil, and hempseed-oil. 



1415. Linseed oil is obtained from the seeds of flax, which are 1417. Poppy-oil is extracted from the seeds of papaver somni- 

 generally roasted before they are subjected to any other process, ferum, which is cultivated in France and Holland for this pur- 

 for the purpose of drying up their mucilage and separating pose. It is clear and transparent, and dries readily ; and when 

 more oil. p^jg jj jg without taste or odor. It is used for the same pur- 



1416. Nut-oil is extracted from the fruit of corylus avellana, poses as the olive-oil, for which it is often sold, and possesses 

 or juglans regia. The kernel is first slightly roasted, and the nothing of the narcotic properties of the poppv. 



oil then expressed. It is used in paintings of a coarser sort; 1418. Hempsced-M is extracted from the seed of the hemp, 



and also m the seasoning of food by many of the inhabitants of It has a harsh and disagreeable taste, and is used by painters m 



the middle .departments of France ; but it is apt to become this country, and very extensively for food in Russia, 

 rancid. 



1419. Volatile oils. Volatile oils, which are known also by the name of essential oils, are of very common 

 occurrence in the vegetable kingdom, and are found in almost all the different organs of the plant. They 

 arc found in many roots, to which they communicate a fragrant and aromatic odor, with a taste somewhat 

 acrid. ^ The roots of inula helenium, genista canariensis, and a variety of other plants, contain essential 

 oils. They are found also in the bark of laurus cinnamomum, of laurus sassafras, and pinus ; in the leaves 

 oflabiateplants, such as mint, rosemary, marjoram; and of the odorous umbcJlifcra;, such as chervil. 



