VEGETABLE PRODUCTS. 



143 



cinal property of certain vegetables, liaa also 

 been ascertained to possess an alkaline quality. 

 This narcotic principle is obtained from the 

 milky and proper juices of some vegetables, and 

 from the infusion of the leaves or stem of others. 

 It exists in great quantity in the concrete juice 

 of the poppy, and is known as opium. It is 

 soluble in boiling water and alcohol, as well as 

 in aU acids. When distilled it emits white va- 

 pours, which are condensed into a yellow oil. 

 Sotlae water and carbonate of ammonia pass into 

 the Receiver, and at last carbonic acid gas, am- 

 monia,- and carbm-etted hydrogen are disengaged, 

 and a bulky charcoal is left behind. Many other 

 substances besides opium possess narcotic quali- 

 ties. Thus the inspissated juice of the garden 

 lettuce resembles opium in its appearance and 

 qualities, and is obtained in a similar manner. 

 The deadly night shade furnishes a narcotic sub- 

 stance, as do also hemlock, black hellebore, 

 strammonium, and fox-glove. All these are active 

 poisons, if taken in large quantity. 



Vegetahle acids. The acids derived from the 

 vegetable kingdom have been multiplied by 

 modem chemists to the number of 116. Some 

 of these acids exist ready formed in the juices 

 of the plant, as the acetic, oxalic, citric, malic, 

 &c.; others are in certain states of combination, 

 and do not exhibit their acid qualities untU arti- 

 ficially decomposed, such as the camphoric, su- 

 beric, pyrolignous, &c. 



Oxalic acid. If the^expressed Jui^e of the 

 wood sorrel, {oxalis acetocella) is left to evaporate 

 slowly, it deposits small crystals of a yellowish 

 colour and saltish taste, which ai-e known by 

 the name of salt of sorrel, that is, a salt with ex- 

 cess of acid; from which the acid maybe obtained 

 pure, by a simple chemical process. Oxalic acid, 

 in its pure state, is always solid. Its taste is 

 sharp and acrid. It is readily soluble in cold 

 water, and is distinguished from other acids by 

 its property of decomposing all calcareous salts, 

 and forming with lime a salt insoluble in water. 

 Hence it is used by chemists as a test to detect 

 the presence of calcareous salts. But it is not 

 used in medicine or the arts, except in its state 

 of acidulum, in which it is employed to make 

 a sort of lemonade, and to discharge stains of 

 ink. It has been found also in oxalis corniculata, 

 geranium aciduum,m^\.^ several species of rumex, 

 and in the pubescence of cicer arietinum. 



Acetic acid, or vinegar, which is generally man- 

 ufactured from wine or sugar in a certain stage 

 of fermentation, has also been found ready formed 

 in the sap of several trees, as analysed by Vau- 

 quelin; and also in the acid juice of the cicer 

 arietinmn, of which it forms a constituent part. 

 It was obtained also by Scheele from the sap of 

 the sambuGus nigra, and is consequently to be 

 regarded as a native vegetable acid. It is dis- 

 tinguished from other vegetable acids by its 



fonning soluble salts with the alkalies and 

 earths. 



Citric acid. This substance exists in the 

 juice of the lemon. It has an agTceable acidu- 

 lous taste, especially when diluted with water. 

 By a red heat it yields carbonic acid gas, and 

 carburetted hydrogen gas, and is reduced to char- 

 coal. Nitric acid converts it into oxalic and 

 acetic acid; and with lime it forms a salt insol- 

 uble in water. It is much used as lemon juice 

 to give a seasoning to liquors, which it does 

 equally weU in its concentrated state also. It 

 has been found in an unmixed state in the fol- 

 lowing vegetable substances: in the juice of 

 oranges and lemons, and in the hemes of vaccin- 

 ium oxt/coccus, vitis idcea, prunus padus, solarium 

 dulcamara, and rosa canina, as well as in many 

 fruits mixed with other acids. 



Malic acid. This acid is found in the juice 

 of unripe apples, whence it derives its name; but 

 it is found also in the juice of berben-ies, elder- 

 berries, gooseben-ies, plums and common house 

 leek. It cannot be obtained in a crystallized 

 and solid form; but if left exposed to the air, it 

 becomes thick and viscous. It is decomposed 

 by heat and strong acids; nitric acid converts it 

 into oxalic acid. It combines with the alkalies 

 and several of the metals, and forms with lime 

 a soluble salt, by which test it is distinguished 

 from other acids. It is used chiefly in the la- 

 boratory. 



Gallic acid. This acid is derived chiefly from 

 nut galls, by exposing a quantity of the powder 

 to a moderate heat in a glass retort, where the 

 acid will form on the top in octohedral crystals. 

 Its taste is austere and astringent; and it reddens 

 vegetable blues. It is soluble both in water and 

 alcohol, and communicates to solutions of iron 

 a deep purple or black colour. When exposed 

 to a gentle heat, it sublimes without alteration; 

 but a strong heat decomposes it. Nitric acid 

 converts it into the malic and oxalic acids. It 

 is of great utility in the art of dyeing, and forms 

 the basis of all black colourSj and of those with 

 a dai-k ground. It is an excellent test of the 

 presence of iron, and with the sulphate of u'on 

 or copperas it forms common wilting ink. 



Tartaric acid. In old wine which has been 

 kept in a cask, a sediment is precipitated which 

 adheres to the sides and bottom, and forms a 

 crust known by the name of tartar, which is a 

 combination of potass and a peculiar acid in 

 excess. The compound is supertartrate of potass 

 and the acid in its state of purity is the tartaric 

 acid with potass; it forms a salt that is with 

 difficulty soluble. It exists in the following 

 vegetable substances : in the pulp of tamarinds, 

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

 sumac; and the roots of triticum repens, and 

 leontodon taraxacum. It is not much used except 

 by chemists; but the supertartrate, from which 



