RADICALS, in chemistry. A radical is a term introduced by one of the fathers in chemistry, Guyton de ltiorveau, in 1787, but its signification was • then more restricted than now, because chemistry was then a more restricted science. Its gen eral meaning, however, allowed it to be gradually extended as the science advanced. It was used to signify a substance which, uniting with oxygen, would form an acid: in other words, it might be called an acidifiable base, either simple or compound. As the science of chemistry advanced and the number of compounds which were studied and produced multiplied, the, word radical became to be applied to any simple or compound body possessing the power of uniting with an clectro-negative body, or element, to form an acid, neutral, or basic body. But the term is principally applied to compound bodies which are held together in such a way that they do not always break up when the com pound of which they form a part is decomposed, or, if they do break up, hold an ele mental relation to it. The idea of a compound radical may be expressed thus: Suppose one or more of the component atoms of a fully saturated compound molecule to he removed; it is clear that tile remaining molecule or group of atoms will no longer he saturated, lint will have a combining power corresponding with the number of units of equivalency removed. Such a remaining molecule or group of atoms is a radical. 'Methane is a fully saturated compound, CH4, but, if one of its hydrogen atoms is :removed, thane will be left the radical methyl, CIL, one molecule of which has the power to unite with one molecule of a univalent element, or two molecules with one molecule of a bivalent element, etc. Ammonia, NB., in which the nitrogen is trivalent, yields,
the removal of a molecule of hydrogen the univalent radical amidogen, with one molecule of potassium, forms potassamine, NILK, and when combined with one molecule of the univalent radical methyl, CIL, forms methylamine, NH,CH,. The loss of two molecules of hydrogen from ammonia leaves the bivalent radical imidbgen, NH, which, with two molecules of methyl, forms dimethylamine, NII2CIL, while the removal of all three of the hydrogen molecules from ammonia leaves nitrogen alone, which often acts the part of a trivalent radical, as for example, when uniting with three molecules of potassium to form. tri-potassamine, NKr, or with three molecules of methyl to form tri-methylamine, N3CH,. Again, a molecule of water, 11.0, when losing a molecule of hydrogen, becomes the radical hob oxyle, HO, a body analogous in its affinities to chlorine, bromine, and 'iodine. Water, HO,H may therefore be compared to hydrochloric acid, CIH, in which the hydroxyle replaces chlorine, or the contrary, while potassium hydroxide, KHO, may be compared to potassium chloride, KU See CHEM ISTRY.
RADIOLI'TiS, a genus of lamellibranchiate mollusca, found only in cretaceous rocks, and remarkable for the great diversity of its valves. The upper valve is flat or conical, with a central umbo; and the lower is an elongated cone, and has on its inner surface two large dental sockets, and lateral muscular impressions. The upper valve is not per= forated with canals, as in the nearly related genus hippurites. More than forty species have been described.