^^6 SCIENCE OF AGRICULTURE. Part II. 



besides opium possess narcotic qualities though they have not yet been minutely analysed. The following are 

 the most remarkable : The inspissated juice of lettuce, which resembles opium much in its appearance, is 

 obtained by the same means, and possesses the same medical virtues ; the leaves of A'tropa Belladonna, 

 or deadly nightshade, and indeed the whole plant ; the leaves of DigitMis purptirea, or foxglove ; and 

 lastly, the following plants, //yosc:p^amus niger, Cbnium maculktum, Dathra Stramonium, and iedum 

 pali'istre, with many others belonging to the Linnean natural order of LiiridEB. 



14'J3. Acids. Acids are a class of substances that may be distinguished by their exciting on the palate 

 the sensation of sourness. They exist not only in the animal and mineral, but also in the vegetable, 

 kingdom ; and such of them as are peculiar to vegetables have been denominated vegetable acids. Of 

 acids peculiar to vegetables chemists enumerate the following : the oxalic, acetic, citric, malic, gallic, 

 tartaric, benzoic, and prussic, which exist ready formed in the juices or organs of the plant, and are 

 ajccordingly denominated native acids ; together with the mucous, pyromucous, pyrotartarous, pyrolignous, 

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

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



W'i^. Oxalic acid. If the expressed juice of the O'xalisAceto- blues. It is soluble both in water and alcohol ; and is distin- 

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

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

 name of the acidulum of sorrel, that is, a salt with excess ot 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 great utility in the art of dyeing, and forms the basis of all 

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

 ployed 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 

 ink. It has been found also in (/xalis comiculkta, Pelarg6nium presence of iron. 



^cidum, in the several species of /iiimex, and in the pubes- 1429. Tartaric acid. If wine is kept for a length of time in a 



cence of Cicer arietlnum. cask or other close vessel, a sediment is precipitated which 



1425. Acdic 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 tartrate 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 Clcer arietinum, of which it forms a constituent part. racterised by its property of forming with potass a salt that 



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



ni^a ; 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 sumach, and 



forming soluble salts with the alkalies and earths. the roots of Afp-opyrum repens and Ledntodon Taraxacum. It 



14W. CUric acid. Citricacidistheacid which exists in the juice is not much used except among chemists; but the tartrate, 

 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 tartar, 

 yields carbonic acid gas and carbonated hydrogen gas, and is 1430. Benzoic acid. From the MJrax Benzbin 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 its aromatic odour 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 Oxyc6ccus palvistris, Kaccinium Kitis Idse'a, storax ; and is used in pharmacy, in the preparation of boluses 

 C^rasus Pkdus, Solanum Dulcamara, and fidsa canina. It has and electuaries, 

 been found also in many other fruits, mixed with other acids. 1431. Prussic add. The prussic acid is generally classed 



1427. Malic acid. Malic acid is found chiefly in the juice of among the animal acids, because it is obtained in the greatest 

 unripe apples, 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, and to exist in vegetable substances also, and it is procured by dis- 

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



1428. Gallic acid. Gallic acid, as it is obtained in the greatest bitter almonds. When pure, it exists in the form of colourless 

 abundance, so it derives its name, from the nut-gaU, from fluid, with an odour resembling that of peach tree blossoms. It 

 which it maybe 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 in a glass retort ; when 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 litUe alkali added to it, mto solutions conteuning 

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



1432. All vegetable acids contain carbon, oxygen, and hydrogen, in one proportion 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. 



1433. 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. 



1434. Fixed oils. Fixed oils are but seldom found, except in the seeds of plants, and chiefly in such as 

 are dicotyledonous. They are found also, though rarely, in the pulp of fleshy fruits, as in that^f 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 vapour of boiling water, or of roasting, before they are subjected to the press. P'ixed 

 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 colour, which is for the most part green or yellow. Its specific gravity is 

 to water as 9403 or 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 

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

 appearance ot 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 crystallises, 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 volatilised till 

 it begins to boil, which is at 600 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- 

 l>arent substance. 



1435. The principal species of fat oils are the following : 



1436. Olive oil, which is expressed from the pulpy part of the pounded in mortars of marble into a paste, which is afterwards 

 ruit of Olea europae'a. The fruit 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 1438. Rapeaeed oil, which is extracted from the i?rdssica A'apus 



top of the water in the vessel beneath. It is manufactured and campdstris. 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 preceding, and is manufactured chiefly in 



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



1437 Oil of almowh, which is extracted from the finit of the 1439. Oil ofbehen, which Ls extracted from the fruit of the 



.^mygdalus communis or common almond. The almonds are JMrorj'n^a ptery^osp^rma, 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 odour, and is on this ac- 



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



1440. The principal species of drying oils are linseed oil, nut oil, poppy oil, and hempseed oil. 



