Intermediate physics / by W. Watson.

  • William Watson
Date:
1912
Catalogue details

Licence: In copyright

Credit: Intermediate physics / by W. Watson. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

    95/588 page 75
    38. States of Matter.—For the purposes of subdivision we may- say that matter exists in three distinct states, the solid, the liquid, and the gaseous. In addition, however, to states which fulfil the definitions of a solid, a liquid, or a gas, which we shall give later on, it will be found that there are intermediate states which bridge over the intervals between the solid and the liquid, and the liquid and the gas. As an example of the kind of gradation which exists, we may take the following: steel, lead, wax, cobbler's-wax (which will flow like a liquid if allowed sufficient time), treacle, water, ether, liquefied carbon dioxide, steam, sulphur dioxide, air, hydrogen. In addition there is the critical state when a substance is to all intents and purposes both a liquid and a gas. We may define a solid as a portion of matter which is able to support a steady longitudinal stress without lateral support. In contradistinction, a portion of matter which is unable to support a steady longitudinal stress without lateral support is called a fluid. If we take a solid body, say a lead-pencil, then we may apply a de- forming force, either of compression or extension, in any direction to the pencil, and there will be a certain amount of strain, either elongation, compression, or bending, produced, which will call into play a stress that, so long as the deforming force is not too great, will be in equilibrium with this force^ and this stress will be produced without the body being supported in any way in a direction at right angles to that along which the stress acts. In the case of a fluid, such as water or air, we are unable to exert a stress on it, and hence produce a corresponding strain, unless we supply some constraining boundary which shall prevent the fluid swelling out at right angles to the line of action of the stress. Thus if we have a fluid enclosed in a cylindrical tube between two pistons, then we may apply a deforming force to the fluid either by forcing the pistons towards one another, or by pulling them apart, in one case producing a compression, and in the other a tension in the direction of the axis of the tube, and a stress will in both cases be produced in an opposite direction to the applied force. If, however, part of the wall of the tube between the pistons is removed, and we then attempt to apply stress to the liquid, we shall not succeed, for either the liquid will flow out through the gap in the tube, or air will be sucked into the tube through this opening, and the fluid will remain unstrained. It is only, therefore, when the column of fluid is laterally supported by the walls of the tube that it is capable of exerting a longitudinal stress. Fluids are divided into liquids and gases. A liquid is a fluid such that when a certain volume is introduced into a vessel of greater volume it only occupies a portion of the vessel equal to its own volume. A gas is a fluid such that if a certain volume is introduced into a vessel, then,
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