Book I. VEGETABLE CHEMISTRY. 217 



artificial, and altogether effected without the operation of natural caueee. "When the Juices are encloeed 

 in vesicles lodged in parts that are isolated, or may easily be isolated, the yeslcles may be opened by means 

 of rasps or graters, and the juices expressed by the hand, or by some other fit instrument. Thus the 

 volatile oil may be obtained that is lodged in the rind of the lemon. When the substance to be extracted 

 lies more deeply concealed in the plant, or in parts which cannot be easily detached from the rest, it may 

 then become necessary to pound or bruise the whole, or a great part of the plant, and to subject it, thus 

 modified, to the action of the press. Thus seeds are sometimes treated to express their essential oils. 

 And if by the action of bruising or pressing heterogeneous ingredients have been mixed together, they 

 may generally be separated with considerable accuracy by means of decantation, when tlie substances 

 held in suspension have been precipitated. Thus the acid of lemons, oranges, gooseberries, and other 

 fruits, may be obtained in considerable purity, when the mucilage that was mixed with them has 

 subsided. 



1367. The chemical processes are such as are affected by the agency of chemical powers, and may be 

 reduced to the following : distillation, combustion, the action of water, the action of acids and alkalies, 

 the action of oils and alcohols, and lastly fermentation. They are much more intricate in their nature 

 than the mechanical processes, as well as more difficult in their application. 



1368. Of the products of vegetable analysis, as obtained by the foregoing processes, some consist of several 

 heterogeneous substances, and are consequently compound, as being capable of further decomposition ; 

 and some consist of one individual substance only, and are consequently simple, as being incapable of 

 further decomposition. 



Sect. I. Compound Products. 



1369. The compound products of analysis are very numerous in themselves, and much 

 diversified in their qualities. They are gum, sugar, starch, gluten, albumen, fibrina, 

 extract, tannin, coloring matter, bitter principle, narcotic principle, acids, oils, wax, 

 resins, gum resins, balsams, camphor, caoutchouc, cork, woody fibre, sap, proper juice, 

 charcoal, ashes, alkalies, earths, metallic oxides. 



1370. Gum is an exudation that issues spontaneously from the surface of a variety of plants in the 

 state of a clear, viscid, and tasteless fluid, that gradually hardens upon being exposed to the action of 

 the atmosphere, and condenses into a solid mass. It issues copiously from many fruit-trees, but especially 

 from such as produce stone-fruit, as the plum and cherry-tree. From plants or parts of plants containing 

 it, but not discharging it by spontaneous exudation, it may be obtained by the process of maceration in 

 water. 



1371. The uses of gum are considerable. In all its varieties it is capable of being used as an article of 

 food, and is highly nutritive, though not very palatable. It is also employed in the arts, particularly in 

 calico-printing, in which the printer makes choice of it to give consistency to his colors, and to prevent 

 them from spreading. The botanist often uses it to fix his specimens upon paper, for which purpose it is 

 very well adapted. It forms likewise an ingredient in ink ; and in medicine it forms the basis of many 

 mixtures, in which its influence is sedative and emollient. 



1372. Sugar is the produce of the saccharum oflScinarum. The canes or stems of the plant, when ripe, 

 are bruised between the rollers of a mill, and the expressed juice is collected and put into large boilers, in 

 which it is mixed with a small quantity of quicklime, or strong ley of ashes, to neutralise its acid, and is 

 then made to boil. The scum which gathers on the top during the process of boiling is carefully cleared 

 away ; and when the juice has been boiled down to the consistence of a syrup, it is drawn off" and allowed 

 to cool in vessels which are placed above a cistern, and perforated with small holes, through which the 

 impure and liquid part, known by the name of molasses, escapes ; while the remaining part is converted 

 into a mass of small and hard granules of a brownish or whitish color, known by the designation of raw 

 sugar, which when imported into Europe is further purified by an additional process, and converted by 

 filtration or crystallization into what is called loaf sugar, or refined sugar, or candied sugar. The juice of 

 the acer saccharinum, or American maple, yields sugar in such considerable abundance as to make it an 

 object with the North American farmer to manufacture it for his own use. A hole is bored in the trunk 

 of the vegetating tree early in the spring, for the purpose of extracting the sap ; of which a tree of ordi- 

 nary size, that is, of from two to three feet in diameter, will yield from one hundred and fifty to two 

 hundred pints and upwards, in a good season. The sap, when thus obtained and neutralised by lime, 

 deposits, by evaporation, crystals of sugar in the proportion of about a pound of sugar to forty pints of 

 sap. It is not materially ditterent in its properties from that of the sugar-cane. The juice of the grape, 

 when ripe, yields also a sugar by evaporation and the action of pot-ashes, which is known by the appella- 

 tion of the sugar of grapes, and has been lately employed in France as a substitute for colonial sugar, 

 though it is not so sweet or agreeable to the taste. The root of beta vulgaris, or common beet, yields 

 also, by boiling and evaporation, a sugar which is distinguished by a peculiar and slightly bitter taste, 

 owing perhaps to the presence of a bitter extractive matter which has been found to be one of the con- 

 stituents of the beet. Sugar has been extracted from the following vegetables also, or from their produc- 

 tions : from the sap of the birch, sycamore, bamboo, maize, parsnep, cow-parsnep, American aloe, dulse, 

 walnut-tree, and cocoa-nut-tree ; from the fruit of the common arbutus, and other sweet-tasted fruits ; 

 from the roots of the turnip, carrot, and parsley ; from the flower of the euxine rhododendron ; and from 

 the nectary of most other flowers. 



1373. The utility of sugar, as an aliment, is well known ; and it is as much relished by many animals 

 as by man. By bees it is sipped from the flowers of plants, under the modification of nectar, and con- 

 verted into honey ; and also seems to be relished by many insects, even in its concrete state ; as it is also 

 by many birds. By man it is now regarded as being altogether indispensable, and though used chiefly to 

 give a relish or seasoning to food, is itself highly nutritive. It is also of much utility in medicine, and 

 t;elebrated for its anodyne and antiseptic qualities, as well as thought to be peculiarly efficacious in pre- 

 venting diseases by worms. 



1374. Starch. If a quantity of wheaten flour is made into a paste with water, and kneaded and 

 washed under the action of a jet, till tlie water runs off colorless, part of it will be found to have been 

 taken up and to be still held in suspension by the water, which will, by-and-by, deposit a sediment that 

 may be separated by decantation. This sediment is starch, which may be obtained also immediately from 

 the grain itself, by means of a process well known to the manufacturer, who renders it finally fit for the 

 market by washing and edulcorating it with water, and afterwards drying it by a moderate heat. Starch, 

 when thrown upon red-hot iron, burns with a kind of explosion, and leaves scarcely any residuum behind. 

 It has been found by the analysis of Gay JLussac and Thenard, to be composed of carbon 43-55 ; oxygen 

 49-68 ; hydrogen 6-77 ; total lOO". This result is not very widely different from that of the analysis of 

 sugar, into which, it seems, starch may be converted by diminishing the proportion of its carbon, and 

 increasing that of its oxygen and hydrogen. This change is exemplified in the case of the malting of 

 barley, which contains a great proportion of starch, and which absorbs during the process a quantity of 

 oxygen, and evolves a quantity of carbonic acid ; and accordingly part of it is converted into sugar 

 Perhaps it is exemplified also in the case of the freezing of potatoes, which acquire in consequence a sweet 

 and sugary taste^ and are known tp contain a great deal of starch, which may be obtained as follows : let 

 the potatoes be taken and grated down to a puJp, and the pulp placed upon a fine sieve, and water made 



to pass through it : the water will be found to have carried off with it an infinite number of particles. 



