Elements of chemistry : including the recent discoveries and doctrines of the science / by Edward Turner.

  • Turner, Edward, 1798-1837.
Date:
1829
Catalogue details

Licence: Public Domain Mark

Credit: Elements of chemistry : including the recent discoveries and doctrines of the science / by Edward Turner. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    and cold, which we experience, are owing to a like cause. On touch- ing a hot body, caloric passes from it into the hand, and excites the feeling of warmth; when we touch a cold body, caloric is communi- cated to it from the hand, and thus produces the sensation of cold. As the transportation of caloric is constantly going forward, it is important to determine by what means, and according to what laws, the equilibrium is established. When any substance is brought into contact with another, which differs from it in temperature,—if, for example, a cold bar of iron be thrust among glowing embers, or a hot ball of the same metal be plunged into a basin of cold water,—the excess of caloric in the hot body passes rapidly to the particles on the surface of the other; from them it is transferred to those situated more internally, and so forth, till the bar in the one case, and the ball in the other arrive at the same temperature as the embers or the water with which they are in contact. In such instances, caloric is said to pass by communication, or to be communicated from one body to another; and in its passage through any one of those bodies, it is said to be con- ducted by them. But when a heated substance is placed under such circumstances as to preclude the possibility of its caloric being communicated,—for instance, when a glass globe full of hot water is suspended in the vacuum of an air-pump,—the excess of its caloric still passes away, and in a very short time it will have acquired the temperature of the surrounding objects. It must then be capable of passing from one body to another situated at a sensible distance; it is projected as it were from one to the other. In order that its passage should take place in this manner, it is not necessary that the body should be in vacuo ; it passes with equal facility through the air as through a vacuum. It follows, therefore, that in establishing an equilibrium of tempera- ture, caloric is distributed among the surrounding objects in two ways; partly thiough the means of intermediate bodies, or by communica- tion, partly in consequence of an interchange established from a distance, or by radiation. Communication of Caloric. Caloric passes through bodies with different degrees of velocity. Some substances oppose very little impediment to its passage, while it is transmitted slowly by others. Daily experience teaches, that though we cannot leave one end of a rod of iron for some time in the fire, and then touch its free extremity, without danger of being burnt; yet this may be done with perfect safety with a rod of glass or of wood. The caloric will speedily traverse the iron bar, so that at the distance of a foot from the fire, it is impossible to support its heat; while we may hold a piece of red hot glass two or threje inches from its extremity, or keep a piece of burning charcoal in the hand, though the part in combustion is only a few lines removed from the skin. The observation of these and similar facts has led to a division of bodies into conductors and non-conductors of caloric. The former division, of course, includes those bodies which allow caloric to pass freely through their substance, such as metals; and the latter com- prises those which do not give an easy passage to it, such as stones, glass, wood and charcoal. Various methods have been adopted for determining the ^relative conducting power of different substances. The most convenient is