American Heritage® Dictionary of the English Language, Fourth Edition
- n. An instrument used to measure thermal expansion and dilation in solids and liquids.
Century Dictionary and Cyclopedia
- n. An instrument for the determination of the changes of volume of a substance or for the measurement of its linear expansion. The form used for the determination of the relative expansion of liquids is essentially a thermometer with a greatly enlarged bulb. The bulb, including a portion of the neck, is filled with the liquid the expansion of which is to be measured, and the position of the end of the liquid column in the neck is noted at different temperatures. Fig. 1 shows such a dilatometer used in the determination of the coefficient of expansion of liquids containing gases in solution. The neck is bent vertically downward and the open end is submerged in a vessel of mercury. Upon cooling the liquid within the bulb the mercury column rises in the neck, and its position is noted upon a scale attached to the neck for that purpose. For the measurement of the expansion of gases an instrument similar to the air-thermometer is employed. The dilatometer in this case consists of a glass bulb (fig. 2) the neck of which is connected with a mercury manometer. The gas may thus be maintained at constant pressure and its change of volume observed, or the pressures may be varied in such a way as to keep the gas at constant volume. For the measurement of the cubic expansion of solids a modification of the dilatometer for iquids has been employed by Dulong and Petit, Regnault, Kopp, and others. In such determinations the solid is inclosed in a glass bulb or tube (fig. 3) the opening of which is then drawn out to form a capillary neck. The space within the bulb not occupied by the solid is completely filled with mercury. When the dilatometer is heated a certain amount of mercury is driven out by the combined expansion of the solid and of the liquid. This is weighed, and from its volume the expansion of the material is computed. The linear expansion of solids is measured in some cases by the direct observation, through microscopes, of parallel lines drawn upon the surface of the test-piece. This method, known as that of Roy and Ramsden, can be employed only when expansion to be measured is that of a long bar, and even for such purposes it has been superseded by more delicate methods. In one form of dilatometer for more refined measurements of the linear coefficient of expansion the bar is fixed at one end, while to the other end, which is free to move with the change of length of the bar, is attached a device for tipping a small mirror. By observing the movement of the image of a scale seen in this mirror, very minute changes in the length of the bar may be detected. The most refined form of dilatometer for the measurement of the linear expansion of solids, and that which is usually employed for this purpose (especially in cases where the size of the test-piece is small, as in crystals), depends upon the interference of light. This extremely sensitive method, in which expansion is measured in the terms of wave-length of light, was first employed by Jamin, whose device, further perfected and developed by Michelson, has become one of the most important of optical instruments, the *interferometer (which see). A special form of interferometer adapted for the rapid and accurate measurement of the linear expansion of solids is the Abbe dilatometer, the principle of which is indicated in fig. 4. In this instrument a glass plate, gg, is mounted above the specimen, S. Both surfaces are plane, but not parallel, so that a thin wedge of air lies between them. A ray of monochromatic light from above is in part reflected from the lower face of gg, and in part from the surface of the specimen. These two reflected rays interfere, and a system of straight parallel interference-bands is formed. Expansion of S diminishes the thickness of the layer of air and consequently the difference of path of the interfering light. From the resulting movement of the fringes the expansion is computed in terms of the wave-length of the light employed. Neither the observing telescope nor the devices for illumination are shown in the diagram. Various other forms of interferometer are employed as dilatometers.
- n. An instrument used to measure the expansion of solids and liquids when heated, or when subjected to some other physical process
GNU Webster's 1913
- n. (Physiol.) An instrument for measuring the dilatation or expansion of a substance, especially of a fluid.
- dilate + -meter. (American Heritage® Dictionary of the English Language, Fourth Edition)
“LEMON: To understand the problem with the current armor, Speyer built an instrument called the differential dilatometer.”
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