372 ACROPHYSICS. 



Among the vegetable acids, are the oxalic, which is poisonous ; the 

 acetic, which is the basis of vinegar ; the tartaric, obtained from 

 crude tartar in the lees of wine ; and the gallic, obtained from gall 

 nuts, and used for ink, and dyeing. The chief vegetable alkalies, are 

 morphia, and narcotina, from opium ; and cinchona and quinia 

 from Peruvian bark. Among the vegetable aliments, are sugar, 

 starch, and gum ; which, by fermentation, produce alcohol, and after- 

 wards vinegar : and among the nitrogenous compounds are gluten, 

 vegetable albumen, and yeast. Indigo, one of the most important 

 coloring matters, also contains nitrogen. 



Animal substances, besides the elements above mentioned, fre- 

 quently contain sulphur, phosphorus, chlorine, potassium, sodium, 

 lime, magnesia, and iron. Among the animal constituents, are fibrin, 

 obtained from muscular flesh; gelatin, or glue, from the skins, car- 

 tilages, and tendons ; and albumen, from the white of eggs, found 

 also in the blood : these being the chief constituents of the fleshy 

 parts, and composed essentially of the four elements named at the 

 head of this section. It is remarkable that while some vegetable 

 substances contain nitrogen, and hence are peculiarly subject to the 

 putrefactive fermentation; the animal oils, tallow, and fat, do not 

 contain nitrogen, and hence are more permanent compounds. When 

 the oils or fats are boiled with potassa, or soda, they are converted 

 into distinct acids, the rnargaric, oleic, and stearic, which unite with 

 these alkalies, and form soaps. The bones of animals, consist chiefly 

 of carbonate and phosphate of lime ; and the blood contains all the 

 chemical elements which are found in the bodies that it nourishes. 



4. The object of Analytic Chemistry, is to examine substances 

 and discover of what chemical elements or constituents they are 

 composed. This it does, by a variety of means, which we have here 

 no room to describe, but of which some examples may be presented. 

 A substance containing free carbon, or carbon combined with hy- 

 drogen, will burn with oxygen ; and the carbonic acid gas and watery 

 vapor, may be collected, and measured, or weighed. Substances 

 which will not burn, are often soluble in water or some other liquid ; 

 and in such cases they may often be tested by the precipitates which 

 they form. Thus, all the sapho-metals, or higher metals, may be 

 precipitated from their solutions, by adding the hydrosulphate of am- 

 monia, or any soluble hydrosulphate ; and several of the metals may 

 be distinguished at once, by the color of the irsulphurets thus preci- 

 pitated. Substances containing silicic acid, as sand, quartz, or flint, 

 may be rendered soluble in water by heating them to redness with 

 a large dose of potassa or soda : and the silicic acid may be separated, 

 by its becoming insoluble on evaporating the solution to dryness. 

 Among the best means of testing substances, is the use of the blow- 

 pipe ; which by the acid of certain fusible salts, called fluxes, will 

 melt most substances and produce certain characteristic effects. 



