AG'GREGA'TION, STATES OF (Lat. ad, to gregarc, to collect into a thud:). The three states, yascoms, liquid, and solid, in whieh matter occurs. substances : 'e capable. under certain conditions of temperature and pressure, of existing in any of the three states. Water. for instance, may be gaseous (steam, or water vapor), liquid (as ordinarily). or solid (ice). Other substances, on the contrary. could, by the means at our disposal, be obtained in only one of the states of aggregation: thus. the clement carbon remains solid even at the highest tem peratures that can be produced at present, and many of its compounds undergo chemical deeom position before reaching the point at which they might certain conditions mat tor has been assumed to be capable of existing in other states besides the above three. Thus. Routigny thought that liquids, when thrown upon glowing hot sur face:, pas: into what he called the spheroidal state. Crookes thought that, at the instant of the electrie discharge, the gases inclosed Within a Crooke: tulle pass into a radiant state. which is eharaeteriZcd Ly certain properties not f01111(1 it the ()thee states of ar7regation. When under
the critical pressure aml temperature (see CRIT I('AL POI NT ) , substances are sometime: said to be in the critical state. In this article, however, only the three states of aggregation that are generally recognized may be briefly character ized.
1. A gas (or vapor) oceupies the volume and assume: the shape of the vessel within which it is inclosed, and its resistance to a change of shape is very small. The amount of work which must ordinarily be expended in diminishing the volume of a gas is also insignificant compared to that required in the case of liquids or solids. An other characteristic property of gases is their capacity of mixing with one another in all pro portions. Gases may be said to be matter in a highly rarefied state, their specific gravity being ordinarily very small compared to that of liquids or of solids. According to the molecular theory, the distances between their particles are very great, and therefore the particles exert very little action upon one another. See AlaEEcULEs-1\T0