Book 1. 



COMPOUND PRODUCTS OF PLANTS. 



151 



whole plant ; the leaves of digitalis purpurea, or foxglove ; and lastly, the following plants, hyoscyamus 

 niger, conium maculatum, datura stramonium, and sedum palustre, with many others belonging to the 

 Linnasan natural order of Lurida;. 



663. 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 ac- 

 cordingly 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 arti- 

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



664. Oxalic acid. If the expressed juice of the oxalis aceto- 

 sella is left to evaporate slowly, it deposits small crystals of 

 a yellowish color and saltish taste, which are known by the 

 name of the acidulum of sorrel, that is, a salt with excess of 

 acid, from which the acid may be obtained pure by processes 

 well known tO' the chemist. It is not used in medicine or 

 the arts, except in its state of acidulum, in which it is em- 

 ployed to make a sort of lemonade, and to discharge stains 

 of ink. It hcis been found also in oxalis corniculata, gera- 

 nium acidum, in the several species of rumex, and in the 

 pubescence of cicer arietinum. 



665. Acetic acid. The acetic acid, or vinegar, which is ge- 

 nerally manufactured from wine in a certain stage of ferment- 

 ation, has been found also ready formed in the sap of several 

 trees, as analysed by Vauquelin ; and also in the acid juice 

 of the cicer arietinum, of which it forms a constituent part. 

 It was obtained also by Scheele from the sap of the sam- 

 bucus nigra ; and is consequently tb be regarded as a native 

 vegetables <acid. It is distinguished from other vegetable acids 

 by its forming soluble salts with the alkalies and earths. 



666. Citric acid. Citric acid is the acid that exists in the juice 

 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 

 yields carlfcnic acid gas and carbonated hydrogene gas, and is 

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

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

 It has been found unmixed with other acids in the following 

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

 in the berries of vaccinium oxycoccus, and vitis idsea, prunus 

 padus, solanum dulcamara, and rosa canina. Ithas been found 

 also in many other fruits, mixed with other acids. 



667. Malic acid. Malic acid is found chiefly in the juice of un- 

 ripe apples, whence it derives its name. But it is found also in 

 tlie juice of barberries, alderberries, gooseberries, plums, and 

 common house-leek. 



668. Gallic 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 ; and the acid 

 will sublime and form crystals of an octahedral figure. Its 

 taste is austere and astringent. It strongly reddens veget- 



able blues. It is soluble both In water and alcohol ; and is dis- 

 tinguished by its property of communicating to solutions of iron 

 a deep purple color. When exposed to a gentle heat it sub- 

 limes vjithout 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 colors, and of colors with a dark ground. It forms also 

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

 presence of iron. 



6G9. Tartaric acid. If wine is kept for alength 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 peculiar acid 

 in excess. The compound is tartarite of potass, and the acid, 

 in its state of purity, is the tartaric acid. It is characterised 

 by the property of its forming with potass a salt that is soluble 

 with difficulty. Ithas been found in the following vegetable 

 substances also ; in the pulp of tamarinds, in the juice of the 

 grape, and mulberries, sorrel, and sumac ; and the roots of 

 triticum repens, and leontodon taraxacum. It is not much 

 used except among chemists. But the tartarite from which 

 it is usually obtained is well known for its medical virtues under 

 the name of cream of tartar. 



670. Benzoic acid. From the styrax benzoin there exudes a 

 resinous substance, known in the shops by the name of l)en/oin, 

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

 from the other acids by its aromatic odor and extreme volatility. 

 It has been obtained also from the balsams of tolu and storax ; 

 and is used in pharmacy, in the preparation of boluses and elec- 

 tuaries. 



671. Prussic acid. Theprussic acid is generally cljissed among 

 the animal acids, becaubi; it is obtained in the greatest abund- 

 ance from animal substances. But it has been proved to exist 

 in vegetable substances also, and is procured by distilling laurel 



resembling that of peach-tree blossoms. It does not j 

 vegetable blues. But it is characterised by its property of 

 fonning a bluish-green precipitate, when it is poured, with a Uttle 

 alkali added to it, into solutions containing iron. 



672. It appears that all vegetable acids contain carbon, oxygen, and hydrogen, in one proportion or other ; 

 and that the prussic acid contains also a {)ortion of nitrogen. The gallic acid contains more of carbon 

 than any other vegetable acid, and the oxalic more of oxygen. 



673. 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. 



674. 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 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 1-000. It is insoluble in water. It is decomposed by 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 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 hydrogene gas, and charcoal ; the product of its combustion is nearly the same ; and hence 

 it is a compound of cart)on, 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. 



675. The pi-incipal species of fat oils are the following : — 



Olive oil, -which is expressed from the pulpy part of the fruit 

 of olea europea. The fruit is first broken in a mill, and reduced 

 to a sort of paste. It is then subjacted to the action of a press, 

 and the oil which is now easily separated swims on the top of the 

 water in the vessel beneath. It is manufactured chiefly in 

 France and in Italy, and is much used throughout Europe in- 

 stead of butter, and to give a seasoning to food. 



Oil of almonds, which is extracted from the fruit of the anry? 

 dalus communis or common almond. The almonds axx. nrst 

 well rubbed or shook in a coarse bag or sack, to separate a bitter 

 powder which covers their epidermis. They are then pounded 



to a paste m mortars of marble, which is afterwards subjected 

 to the action of a press; and the oil is now obtained as in the 

 case of the olive. 



Rapeseed-oil, which is extracted from the brassica na^ius and 

 campestris. It is less fixed and less liable to become rancid 

 than the two former, and is manufactured chiefly in Flanders. 



Oilnfhehen, which is extracted from the fruit of the guilandina 

 mohringa, common in Egypt and Africa. It is apt to become 

 rancid ; but it is without odor, and is, on this account, much 

 used in perfumery. 



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



Puppy-oil is extracted from the seeds of papaver somniferum, 

 which is cultivated in France and Holland for this purpose. It 

 is clear and transparent, and dries readily : and when )>ure it 

 is without taste or odor. It is used for the same purposes as 

 the olive-oil, for which it is often sold, and possesses nothing of 

 the narcotic properties of the popi)y. 



Hempseed-oil is extracted from the seed of the hem)). It has 

 a liar ah and disagreeable taste, and is use<l by painters in this 

 country, atjd very extensively for food in H-ussia. 



4 



Linseed-oil is obtained from the seeds of flax, which are ge- 

 nerally roasted before they are subjected to any other process, 

 for thepurpose of drying up their mucilage and separating more 

 oil. 



Nut-oil is extracted from the fruit of corylus avellana, or ju- 

 glans regia. The kernel is first slightly roasted, and the oil 

 then expressed. It is used in paintings of a coarser sort ; and 

 also in the sezisoning of food by many of the inhabitants of (he 

 middle deiiartments of France ; but it is apt to become rancid. 



