TYPES, CHEMICAL. The idea of referring organic bodies to some simple type or representative, has attracted the attention of many chemists, among whom Dumas, Sterry Hunt, Laurent, and Gerhardt, especially deserve notice. As our limited space prevents us from attempting to trace out the history of the theory, we shall confine our selves to a statement of the outline of the doctrine as laid down by Gerhardt, and now adopted in most recent books on organic chemistry. The four principal types, to which (1) of the chemical compounds are referred, are the following: (1 The hydrogen or metallic type, H (2) The hydrochloric acid or chloride ; (3) The water or oxide and (4) The ammonia or nitride type,H N. The reason why the equivalents of the hydrogen in the hydrogen type, and of the water in the water type. are doubled, is as follows: an accurate study of the volumetric relations of nearly all organic compounds, shows that their molecules furnish equal volumes of vapor, and that the gaseous volume occupied by each molecule will occupy 4 volumes, if oxygen repre sent the unit of volume. Taking the volume of oxygen, 0, as 1, those of hydrogen, H, and of water, HO, are, as is well known, 2. Hence, to fix the standard of comparison at 4 volumes of oxygen, we must write or H , or or H Oa, instead of the apparently simpler forms, H and HO. In the other cases, this modification is unneces sary, as the gaseous volumes of hydrochloric acid (HCI) and ammonia are in accordance with the general laws, and are equal to 4 standard volumes. • 1. The hydrogen type, Hincludes, according to Gerhardt, the radicals of the alco hols, marsh gas, and the hydrocarbons homologous with it, the aldehyds, etc. Thus, marsh gas (or hydride of methyl), is written 04HH,, according to the type theory, O H, and aldehyd (hydride of acetyl), C4H40a, is written H, ; or both the upper and lower equivalent of hydrogen in the typical formula may be repeated. Thus, acetone or methylide of acetyl, = . Among the compounds of inorganic chemistry belonging to this type, Gerhardt places the hydrides, arseuides, and antemon ides of the metals.
2. The hydrochloric acid , is removed by many chemists from the primary or principal types, and is regarded as a derived type from the preceding one, one equiv alent of H being here replaced by one of chlorine. It includes the chlorides, fluorides, iodides, bromines, cyanides, the ethers of the hydracids, etc. As examples, we may 1150 2 take chloride of benzoyl, C, = 014, hydrochloric ether, = Cl and iodide of ethyl, = 3. The 'water type, H II )- includes the oxides (in which term are embraced acids, bases, and salts), the sulphides, the alcohols, the simple and compound ethers, the mono basic organic acids, etc. The following are a few examples: methyl alcohol or wood spirit, C21140, = ) common alcohol, = Cjia ) 0 • acetic acid, 11H H C H 0 = Oa ' • acetate of potash, KO,C.,HaCoa = Oa; acetic ether, = Oa; common ether = } etc. I ) 4. The ammonia type, H s-N, includes the nitrides and phosphides, the compound S ammonias, and the amides; as, for example, ethylamine or ethylia, 0,117N = H N ; 11 trimethylamiue or trimethylia, = N; benzamide, C141:17N0a = N, etc.
Fl Besides these three or four principal types, there are derived types, multiple types, and mixed types; and under one or other of these types, primary and derived, multiple and mixed, all organic compounds can be arranged; and the theory of types leads to the general conclusion, that all organic compounds, or, more strictly speaking, their mole cules, may be regarded as molecules of hydrogen, water, ammonia, hydrosulphurie acid, etc. in which the hydrogen is entirely, or in part, replaced by organic radicals.—For further information on this subject, the reader is referred to Odling s Lectures OIL Anon& Chemistry, 1866, and to the second volume of Gorup Besanez, Lehrbuch dcr Claude, pp. 24-48. The chapter "On types," from this volume, has been reprinted separately in the form of a pamphlet.