790 



VEDAS VEGETABLE CHEMISTRY. 



round its centre, and with which it describes areas 

 proportional to the times. 



VEDAS. See Indian Literature. 



VEDETTE; a sentinel on horseback. The 

 word is derived from the Italian vedetta (from 

 vedere, to see), and signifies, originally, a watch- 

 tower. It is also used, sometimes, for sentinels on 

 foot, forming the extreme point in the line of out- 

 posts. They are often placed in pairs, in surh a 

 way that the field of vision of one intersects that 

 of the other. 



VEERING. See Ship. 



VEGA (Spanish for valley") ; the name of nu- 

 merous places in countries where the Spanish lan- 

 guage is spoken. 



VEGA. DON LOPE FELIX DE VEGA CARPIO, 

 generally called Lope dc Vega, is described under 

 Lope de Vega. See also Garcilaso. 



VEGA, GEORGE, baron de, an Austrian officer 

 of artillery, born at Sagoritz, in Carniola, in 1754. 

 He studied at the college of Laybach, where he 

 made a rapid progress in mathematics. Being ap- 

 pointed an engineer in Carniola, and afterwards in 

 Hungary, lie became known as a man of talent in 

 his profession, and was patronised by the emperor 

 Jose;ih II. He served in several campaigns against 

 the French, and, having distinguished himself on 

 many occasions, especially in 1796, was made a 

 tniijor, and afterwards a lieutenant-colonel, knight 

 of the order of Maria Theresa, and a baron of the 

 empire. His death took place in September, 1802. 

 He was a member of the academies of Gottingen, 

 Erfurt, Berlin, and several others, and was con- 

 sidered as a distinguished mathematician. He pub- 

 lished a Course of Mathematics for the Use of the 

 Artillery of the Imperial Army (Vienna, 1786 1800, 

 4 vols., 4to. ; 3d edit., 1802, folio) ; a Logarithmo- 

 trigonometrical Manual (Leipsic, 1793, 4to.) ; a 

 Complete Collection of grand Logarithmo-trigono- 

 mctrical Tables (1794, folio) ; an Introduction to 

 Chronology (Vienna, 1801, 8vo.) ; and a Natural 

 System of Measures, Weights and Coins (1803, 

 4 to.;. 



VEGETABLE CHEMISTRY. The princi- 

 ples of which vegetables are composed, if we pur- 

 sue their analysis as far as our means have hitherto 

 allowed, are chiefly carbon, hydrogen and oxygen. 

 Nitrogen is a constituent principle of several, but 

 it is only present in small quantity. Potash, soda, 

 lime, magnesia, silex, alumine, sulphur, phosphorus, 

 iron, manganese and muriatic acid occur occasion- 

 ally in plants, though in small and very variable 

 proportions. Every distinct compound which ex- 

 ists already formed in plants, and which is capable 

 of separation without suffering decomposition, is 

 called a proximate, or immediate principle, of vege- 

 tables. Thus sugar, starch and gum are proximate 

 principles. Opium, though obtained from a plant, 

 is not a proximate principle, but consists of several 

 proximate principles, mixed more or less intimately 

 together. The proximate principles of vegetables 

 are sometimes distributed over the whole plant, 

 while i'i others they are confined to a particular 

 part. The methods by which they are procured 

 are very variable. Thus gum exudes spontaneously, 

 and the saccharine juice of the maple-tree is ob- 

 tained by incisions made in the bark. In some 

 cases, a particular principle is mixed with such a 

 variety of others, that a distinct process is required 

 for its separation. Of sueh processes consists the 

 proximate analysis of vegetables. Sometimes a 

 substance is separated by mechanical means, as in 



the preparation of starch. On other occasions, ad- 

 vantage is taken of the volatility of a compound, 

 or of its solubility in some particular menstruum. 

 Whatever method is employed, it should be of such 

 a nature as to occasion no change in the comple- 

 tion of the body to be prepared. The reduction 

 of the proximate principles into their simplest parts 

 constitutes their ultimate analysis. By this means 

 the quantity of oxygen, carbon and hydrogen pro 

 sent in any compound is ascertained. The methodby 

 which this is accomplished is, to convert the whole 

 of the carbon into carbonic acid, and the hydrogen 

 into water, by means of some compound which con- 

 tains oxygen in so loose a state of combination ;is 

 to give it up to those elements as a red beat. The 

 substance employed is the peroxide of copper, 

 which, if alone, may be heated to whiteness with- 

 out parting with oxygen ; whereas it yields oxygen 

 readily to any combustible matter with which it is 

 ignited. It is easy, therefore, by weighing it be- 

 fore and after analysis, to discover the precise 

 quantity of oxygen which has entered into union 

 with the carbon and hydrogen of the substance 

 submitted to examination. The constitution of 

 vegetable substances is not yet sufficiently known 

 to admit of their being classified in a purely 

 scientific order. The chief data hitherto furnished 

 towards forming a systematic arrangement, are de- 

 rived from a remarkable agreement between the 

 composition and general properties of several vege- 

 table compounds. From the ultimate analysis of a 

 considerable variety of proximate principles the 

 three following conclusions are drawn: 1. a vege- 

 table substance is always acid when it contains 

 more than a sufficient quantity of oxygen for con- 

 verting all its hydrogen into water ; 2. it is always 

 resinous, oily or alcoholic, &c., when it contains 

 less than a sufficient quantity of oxygen for combin- 

 ing with the hydrogen ; and 3. it is neither acid 

 nor resinous, but in a state analogous to sugar, 

 gum. starch, or the woody fibre, when the oxygen 

 and hydrogen which it contains are in the exact 

 proportion for forming water. These laws, indeed, 

 are not rigidly exact, nor do they include the vege- 

 table products containing nitrogen. M. Thenard 

 has divided the proximate principles into five 

 classes. The first includes the vegetable acids ; 

 the second, vegetable alkalies; the third, those 

 substances which contain an excess of hydrogen ; 

 the fourth, those the oxygen and hydrogen of which 

 are in proportion for forming water; and the fifth, 

 those bodies which, so far as is known, do not be- 

 long to either of the other divisions. 



1. The vegetable acids are decomposed by a red 

 heat. They are, in general, less liable to sponta- 

 neous decomposition than other vegetable sub- 

 stances. They are nearly all decomposed by con- 

 centrated hot nitric acid, by which they are con- 

 verted into carbonic acid and water. They are at 

 least twenty-five in number, the most important of 

 which are the following: acetic acid, or vinegar, 

 oxalic, tartaric, citric, malic, benzoic, gallic, boletic, 

 moroxylic, meconic and pectic a/iids. 



2. Under the title of vegetable alkalies are com- 

 prehended those proximate principles which are 

 possessed of alkaline properties. They all consist 

 of carbon, hydrogen, oxygen and nitrogen. They 

 are decomposed with facility by nitric acid and by 

 heat ; and ammonia is always one of the products 

 of the destructive distillation. They never exist 

 in an insulated state in the plants which contain 

 them, but are, apparently, in every case, combined 



