CHEMISTRY. 369 



the liquid oil of vitriol; or with iron, to form the solid rust, or oxide 

 of iron. 



An acid, is an electro-negative compound ; which, if soluble, has 

 a sour taste ; and which will combine with alkalies, or bases, to form 

 salts. An alkali, or base, is an electro-positive compound ; which, 

 if soluble, has an acrid taste ; and which will unite with acids, to 

 form salts : these latter being compounds of an acid and base ; and, 

 if soluble, having what is called a saline taste. Many acids, and 

 bases, contain oxygen ; but others contain chlorine, sulphur, or other 

 electro-negative elements, in its stead. An oxide, usually signifies a 

 compound containing oxygen ; and which is neither an acid nor an 

 alkali, though it may be a base. Potassa, is an alkali ; composed 

 of oxygen and the metal potassium : and pearlash is a salt, composed 

 of potassa and carbonic acid. A chloride, is a compound containing 

 chlorine ; and a carburet is one containing carbon. Sulphuric acid 

 contains more oxygen than sulphurous ; and the salts of the former 

 are called sulphates, but those of the latter are termed sulphites. 

 Thus, sulphate of soda, denotes a compound of sulphuric acid and 

 soda ; and arsenite of copper, is a compound of arsenious acid and 

 the oxide of copper. 



Cohesion, is the mutual attraction of homogeneous, or similar par- 

 ticles, causing the formation of solids. Affinity is the mutual attrac- 

 tion of heterogeneous particles, causing the formation of compounds. 

 Thus, by affinity, carbon and oxygen unite, in ordinary combustion, 

 forming carbonic acid ; and this unites with lime, to form carbonate 

 of lime : but, by cohesion, the particles of this compound are aggre- 

 gated, to form solid marble. By affinity, if we add lime water to a 

 solution of pearlash, the lime will seize on the carbonic acid ; and, 

 by cohesion, it will form a white precipitate, or deposite, of carbonate 

 of lime ; leaving the potassa in solution. When distinct compounds 

 are thus formed, the elements, or constituents, are found to unite in 

 certain definite, invariable proportions ; which may be represented 

 by what are called their equivalent numbers, or equivalents. Thus, 

 8 parts by weight of oxygen, unite with 1 of hydrogen, to form 

 water; and with 16 of sulphur, to form hyposulphurous acid: 

 while 1 of hydrogen unites also with 16 of sulphur to form hydro- 

 sulphuric acid. In gaseous compounds, the elements have also a 

 very simple ratio to each other, by bulk, as well as by weight. 



Of the non-metals, Oxygen is a colorless gas, somewhat heavier 

 than the air, and an element of air and water, as well as of nume- 

 rous other compounds. It is essential to animal life ; being converted 

 into carbonic acid when inhaled, as also by the burning of carbon- 

 aceous substances. Various other elements burn or combine with 

 it, forming oxides, acids, alkalies, and earths. Hydrogen, is also 

 a colorless gas ; but 14.51 times lighter than the air : and it burns 

 or explodes, with oxygen, forming water ; which is an oxide of 

 hydrogen, expressed by the formula H + O, or one equivalent of hy- 

 drogen to one of oxygen ; as above mentioned. Nitrogen, is also 

 a colorless gas, found chiefly in the air ; which consists of 1 mea- 

 sure of oxygen to 4 of nitrogen ; or by weight, of 8 of the former 

 to 28 of the latter. Nitrous acid, (N-f 4 O,) is distinguished by its 

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