Matter

gas, solid, liquid, gases, properties and theory

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Matter exists in three (or perhaps four) physical states. All ordinary bodies, for exam ple, may be classified, roughly, either as solids or fluids; fluids being further subdivided into liquids and gases. This classification is not all that could be desired, since there are certain bodies (such as wax) which have certain char acteristics of the solids and certain others of the liquids. A more complete and systematic classification is hardly practicable, however, in the present article. A solid body may be de fined as a body capable of resisting a consider able shearing stress. (See ELASTICITY). Solid bodies usually have a considerable tensile strength also. A solid does not yield continuously to a small deforming force; It resists deformation; and its resistance increases as the deformation increases. A fluid, on the other hand, is a sub stance having almost no shearing strength, and offering very little resistance to forces that tend to change its shape. A fluid yields continuously to a deforming force, and a force that will deform it at all will deform it indefinitely, so long as it is allowed to act. Considering the subdivision of fluids into gases and liquids, we may say that a gas is a fluid that presses con tinuously and in direction upon the walls of the vessel containing it and which follows them indefinitely if they retreat. A gas, if left to itself, tends to expand infinaelv in all direc tions. A liquid is a fluid does not follow the walls of the containing vessel if they retreat and which has no tendency to expand indefi nitely if left to itself. (For the prevalent theories regarding the constitution of matter, See GASES, KINETIC THEORY OF; MOLECULAR THEORY).

When a gas is rarefied very highly by a mer cury vacuum pump, it exhibits properties which i are different in many respects from those mani fested by gases in the ordinary state of density.

The pressure in such a rarefied gas, for exam ple, may be different in different directions; so that in this respect, at least, the rarefied medium resembles a solid rather than a gas or liquid. Mechanical and electrical properties are also ob served at high exhaustions which cannot be re produced at ordinary pressures; and for these and other reasons Crookes considered that a gas, when under only (say) the millionth or ten millionth of an atmosphere of pressure, may be fairly said to constitute a "fourth state of matter," which he considered to be as different from the gaseous state as the gaseous state is from the liquid state. At first thought this ap pears to be an extreme and hardly a justifiable view ; but it must be remembered that Andrews showed that the distinction between a liquid and the gas or vapor obtained from it by evapora tion ceases to exist at temperatures higher than a certain critical value peculiar to each sub stance. (See CRITICAL POINT). This tempera ture is about 88° F. for carbon dioxide, and at temperatures progressively higher than this the isothermals of carbon dioxide approximate with increasing closeness to the hyperbolas of a per fect gas. It might be thought that a critical state exists with reference to the solid and liquid states; but this is still somewhat doubtful. It appears probable that no such state exists between a solid and its liquid, unless the solid is crystalline; and its existence has not been established even for thiS case.

See MOLECULAR THEORY; LIQUEFIED AND COMPRESSED GASES; ELECTRON THEORY', SOLU TIONS; ETHER; VACUUM, etc. Consult, also, Tait, 'Properties of Matter' ; Kimball, 'Physical Properties of Gases' ; Poynting and Thomson, 'Properties of Matter' ; Risteen, 'Molecules and the Molecular Theory of Matter); Leh mann, (Molelcularphysik.)

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