22 > 



sci l.NC m: OF AGRICULTURE. 



II. 



besides opium possess narcotic qualities though they havenol yet been minutely analysed The following are 

 theroosl remarkable :— The inspissated Juice <>i lettuce, which resembles opium much in its apgear ance, is 

 obtained by the same means, and possesses the same medical virtues ; the leaves of A/tropa BelladOnna, 

 oi deadlj nightshade, and indeed the whole plant; the leaves of Digitalis purpurea, or foxglove: ami 

 lastly, the following plants, tfyosc^amua nager, Coniurn maculatum, Dathra Stramonium, &nd Ledum 

 palfistre. with many others belonging t<> the Linnean natural order of Luridae. 



i | ! 1, idi Ar'nl- an- a class of substances that m.iv be distinguished by their exciting on the palate 

 the Bensation of sourness. Theyexisl not only in the animal and mineral, but also in the vegetable, 

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



acid, peculiar tO vegetables chemists enumerate the following: the oxalic, acetic, citric, malic, gallic, 



tartaric bensoic, and prussic, winch exist ready formed in the juices or organs of the plant, and are 

 accordingly denominated native acids ; together with the mucous, pyromucous,pvrotartarou8,pyrolignous, 



camphoric, and BUberic, which «!o not exist ready Conned in the plant, ami are hence denominated unifi- 

 ed*! iicids! They are consequently not within the scope of the object of the present work. 



\\ :\. Oxalic add. Ifthe expressed Juice of the(XxaIteAceto- 



efl to evaporate Jowly, ii (ii-]M^it^ small crystals <>t a 



yellowish colour and which an- known by the 



. i. l, ill it Is, .i salt with excess ot 

 acid, from wldch the m Id mai be oht .md pure hy nrocesses 

 well known to the chemist. Il is not vised in medicine or 

 the arts, except In Its ;tate of addulum, in which it is cm- 



ployed to make ■ s..rt of le Ii - and to di i barge stains .if" 



mk". It has been round also In O'xalis conteulata, Pelargonium 

 aViduin, in the several species of Kuuiex, and in the pubes- 

 t arleUnum. 

 M25. - The acetic acid, or vinegar, which is ge- 



ictured from wine in a certain stage of ferment- 

 been (bund also ready formed In the sap of several 

 i,., , ii bj Vauquelin; and also In the acid juice 



um, of which it forms a constituent part. 

 obtained 1>\ Scheele from the sap of the Sambacus 

 nigra; and U consequents to be regarded as a native vegetable 

 acid. It is distinguished from other vegetable acids by its 

 forming soluble salts with the alkalies and earths. 



1 1 '.0. Citr. ••■!.•!,!. i itric acid is the acid which existsin thejuice 

 of lemon. Its taste is very sour in a state of purity, but ex- 

 ceedingly pleasant when diluted with water. By a red heat it 

 ■field! carbonic acid gas and carbonated hydrogen gas, and is 

 reduced to a charcoal; nitric acid converts it into oxalic and 

 acetic ftcid, and with lime it forms a salt insoluble in water. 

 It his been found unmixed with other acids in the following 

 vegetable substances : in the juice of oranges and lemons, and 

 :i the berries of Oxycdccus palustris, Paccmium Kit is ldce'a, 

 Padus, Sblitnum Dulcamara, and rtosa can'tna. It has 

 been found also in many other fruits, mixed with other acids. 



1127. Malic acid. Malic acid is found chiefly in the juice of 

 unripe apples, whence it derives its name; but it is found also 

 in thejuice of barberries, alderberries, gooseberries, plums, and 

 common house-leek. 



1 1 ,'S. (,.(//;, acid* Gallic acid, as it is obtained in the greatest 

 abundance, so it derives its name, from the nut-gall, from 

 which it may be extracted by exposing a quantity of the powder 

 of nut-galls to a moderate heat in a glass retort ; when the acid 

 will sublime and form crystals of an octahedral figure. Its 

 taste is austere and astringent. It strongly reddens vegetable 



blues. It Is soluble both in water and alcohol; and is distin- 

 guished by its property of communicating to solutions of iron 

 a deep pu**ple colour. When exposed to a gentle heat itsub- 

 UmeS without alteration, but a Strong heal decomposes it. 

 Nitric arid converts it into the malic mtl oxalic acids. It is of 

 great utility in the art of dyeing, and forms the basis of all 

 black colours, and <if colours with a dark ground- It forms also 

 the basis ot ink ; and chemists use it as a test to detect the 

 presence of iron. 



1429* Tartaric "rid. If wine is kept for a length of time in a 

 cask or other close vessel, a sediment is precipitated which 

 adheres to the sides or bottom, and forms a crust known by the 

 name of tartar, which is a combination of potass and a pecu- 

 liar acid in excess. The compound is tartrate of potass, and 

 the add, in its state of purity, is the tartaric acid. It is cha- 

 racterised by its property of forming with potass a salt that 

 iluble with difficulty. It has been found in the following 

 vegetable substances also: in the pulp of tamarinds, in the 

 juice of the grape, and mulberries, sorrel, and sumach, and 

 the roots of Agropyrum repens and I.e6ntodon Taraxacum. It 

 is not much Used except among chemists; but the tartrate, 

 from which it is usually obtained, is well known for its medical 

 virtues under the name of cream of tartar. 



1430. Benzoic acid. From the Myrax Benzoin there exudes a re- 

 sinous substance, known in the shops by the name of ben/oin, 

 and in which the benzoic acid is contained. It is distinguished 

 from the other acids by its aromatic odour and extreme volati- 

 lity- It has been obtained also from the balsams of tolu and 

 storax ; and is used in pharmacy, in the preparation of boluses 

 and electuaries. 



1431. Prusric aciil. The prussic acid is generally classed 

 among the animal acids, because it is obtained in the gr( itesi 

 abundance from animal substances. But it has been proved 

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

 tilling laurel leaves, or the kernels of the peach and cherry, or 

 bitter almonds. MTien pure, it exists in the form of colourless 

 fluid, with an odour resembling that of peach tree blossoms. It 

 does not redden vegetable blues; but it is characterised by its 

 property of forming a bluish-green precipitate, when it is 

 poured, with a little alkali added to it, into solutions containing 

 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. 



11 ft Fixed oils. Fixed oils arc 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 of the olive, 

 which yields l he 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 bv 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 mean's 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. 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 colour, which is for the most part green or yellow. Its specific gravity is 

 to water as 9*403 or I(MK). 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 

 il begins to boil, which is at 600° of Fahrenheit By distillation it is converted into water, carbonic acid, 

 and carburettl <1 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 

 nils and drving oils. The former are readilv inspissated by the action of the air, and converted into a sort 

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

 parent Bllbstance 



U ■ > The principal species of fat oils arc the following : — 



i :.*'.. Otivt oil, winch is expressed from the pulpy r art of the 

 fruit of 0*le ' europata* Tin- fruit i- first broken in a mill, and 

 reduced to a sort ot juste. It is thin subjected to the action of 

 a press, and the oil, which is now easily separated, sv una on the 

 top of the crater in the vessel beneath* Ii is manufactured 



chietly in France and in Italy, and is much used throughout 



Europe In t< id of i miter, and to give a seasoning to food. 



1 137 Oil i?f almond* t which is extrai ted from the fruit of the 

 y^niVgdalu- communis or common almond. The almonds are 

 first well rubbed or shook in a coarse hat; or sack , to separate .\ 

 hitter powder which coven their epidermis. They are then 



pounded in mortars of marble into a paste, which is afterwards 

 sab ected to the action of the press; and the oil is now ob- 

 tain' <i as in the olive. 



1 158. Rapcscedoit, which is extracted from the Brassica A'apus 

 ami campestris. It is less fixed and less liable to become ran* 

 i id ili m the two preceding, and is manufactured chiefly in 

 Klamlers. 



1439* Oil qfbehen, which is extracted from the fruil of the 

 N<>rin<r'i ptervgosperma, common in Egypl and Africa. It is apt 

 tn become rancid ; but it is without odour, and is on this ac- 

 C it mil' ti Used in perfumery. 



1440 The pt 'w <p<ii species oj drying oils are Unseed oil, nut oil, poppy oil, and lieinpsccd oil. 



