Base

Base, in Chemistry, is a term applied to a compound body, generally consisting of a metal united with oxygen. Thus, the metal potassium, K, when it combines with oxygen, O, forms the oxide $K\_2O$, which unites with water, yielding the base potash, or caustic potash, KOH; and similarly lead, Pb, and oxygen, yield the base oxide of lead, or litharge, $PbO$. A distinguishing feature of a base is that it is capable of entering into double decomposition with an acid, more or less neutralising its acid properties, and forming a Salt (q.v.) and water. Thus, the base potash combines with sulphuric acid to form the salt, sulphate of potash, and water, as represented by the following equation:

Potash. Sulphuric Acid. Sulphate of Potassium. Soda.
$K\_2O\; +\; H\_2SO\_4\; =\; K\_2SO\_4\; +\; H\_2O$.

So also potash and nitric acid, $HNO\_3$, yield the salt nitrate of potassium, or nitre, $KNO\_3$. Occasionally sulphur replaces the oxygen in a base. Thus, the metal potassium, K, unites with sulphur, S, to form the sulphur base, sulphide of potassium, $K\_2S$, which can unite with a sulphur acid like sulpharsenious acid or orpiment, $As\_2S\_3$, to make the salt sulpharsenite of potash, $K\_2S,\; As\_2S\_3$. The metal half of a base need not be a simple element, but may be a compound body which, for the time, plays the part of a simple substance. Thus, the compound ethyl, $C\_2H\_5$, can combine with oxygen to form ordinary ether, $(C\_2H\_5)\_2O$; and the base thus produced can, in its turn, combine with acids to form salts. A base may be soluble or insoluble in water. Thus, the bases potash, $K\_2O$, soda, $Na\_2O$, ammonia, $NH\_4HO$, baryta, $BaO$, strontia, $SrO$, lime, $CaO$, and magnesia, $MgO$, are more or less soluble in water; whilst the oxide of iron or rust, $Fe\_2O\_3$, and the red oxide of mercury, $HgO$, are insoluble in water, but soluble in acids. For organic bases, &c., see ALKALIES, ALKALOIDS, and AMINES.