ABSORPTION, in chemistry, absorption is the taking up of a gas by a liquid or by a porous solid; and in natural philosophy it is the taking up of rays of light and heat by certain bodies through which they are passing. Absorp tion of light is the retention of some rays and the reflection of others when they pass into an imperfectly transparent body. If all were absorbed, the body would be black ; if none, it would be white; but when some rays are absorbed, and others reflected, the body is then of one of the bright and lively colors.
In chemistry the coefficient of absorption of a gas is the volume of the gas reduced to Cent. and 760 m.m. pressure, which is absorbed by the unit of volume of any liquid.
Absorption of heat is the retention and con sequent disappearance of rays of heat in passing into or through a body colder than themselves.
Absorption of the earth is a term used by Kircher and others for the subsidence of tracts of land produced by earthquakes.
In physiology absorption consists of a series of complicated processes by which the neces sary constituents of the body are taken in at certain parts to be distributed to the places of need. The chief substances are water and salts, mainly absorbed in the small intestines; fats, chiefly taken in the cells of the intestinal mucosa after a complicated series of chemical changes; carbohydrates chiefly absorbed at vari ous parts of the intestinal canal after conver sion into monosaccharids and proteins which are chiefly taken up by the bloodvessels after pass ing through the epithelial cells of the intestinal mucosa as peptones, proteoses, or amino-acids. Proteids are not absorbed in the stomach. (See