CALORIC. 



ed through all bodies with the same ce- 

 lerity and ease. Those that allow it to 

 pass' with facility are called good con- 

 ductors ; those through which it passes 

 with difficulty are called bad conductors. 



Metals are the best conductors of calo- 

 ric of all the solids hitherto tried. The 

 conducting powers of all, however, are 

 Ho^ equal. Dr. Ingenhousz procured 

 cylinders of several metals exactly of the 

 same size, and having coated them with 

 wax, he plunged their ends into hot water, 

 and judged of the conducting power of 

 each by the length of wax-coating melt- 

 ed. From these experiments he conclud- 

 ed, that the conducting power of the 

 metals which he examined were in the 

 following order : 



Silver, 



Gold, 



Platinum," 



>much inferior to the others, 

 steel, 



Lead, J 



Next to metals, stones seem to be the 

 best conductors ; but this property varies 

 considerably in different stones. Bricks 

 are much worse conductors than most 

 stones. 



Glass seems not to differ much from 

 stones in its conducting power : like 

 them, it is a bad conductor. This is the 

 reason that it is so apt to crack on being 

 suddenly heated or cooled. One part of 

 it, receiving or parting with its caloric be- 

 fore the rest, expands or contracts, and 

 destroys the cohesion. Next to these 

 some dried woods. 



Charcoal is also a bad conductor ; ac- 

 cording to the experiments of Morveau, 

 its conducting power is to that of fine 

 sand -2:3. Feathers, silk, wool, and 

 hair, are still worse conductors than any 

 of the substances yet mentioned. This is 

 the reason that they answer well for arti- 

 cles of clothing. They do not allow the 

 heat of the body to be carried off by the 

 cold external air. Count Rumford has 

 made a very ingenious set of experiments 

 on the conducting power of these substan- 

 ces. He ascertained that their conduct- 

 ing power is inversely as the fineness of 

 their texture. 



Having in the preceding sections con- 

 sidered the nature of caloric, the manner 

 which it moves through other bodies and 

 distributes itself among them, let us now 

 examine, in the next place, the effects 

 which it produces on other bodies, either 

 by entering into them or separating from 



them. The effects which caloric produces 

 on bodies may be arranged under three 

 heads ; namely, changes in bulk ; changes 

 in state ; and changes in combination. 



It may be laid down as a general rule, 

 to which there is no known exception, 

 that every addition or abstraction of calo- 

 ric makes a corresponding change in the 

 bulk of the body which has been subject- 

 ed to this alteration in the quantity of its 

 heat. 



In general the addition of heat increases 

 the bulk of a body, and the abstraction of 

 it diminishes its bulk ; but this is not uni- 

 formly the case, though the exceptions 

 are not numerous. 



Indeed, these exceptions are not only 

 confined to a very small number of bodies, 

 but even in them they do not hold, except 

 at certain particular temperatures ; while 

 at all other temperatures these bodies 

 are increased in bulk when heated, and 

 diminished in bulk by being cooled. We 

 may therefore consider expansion as one 

 of the most general effects of heat. It is 

 certainly one of the most important, as it 

 has furnished us with the means of Mea- 

 suring all the others. See PTKOMETER. 



Though all bodies are expanded by 

 heat, and contracted by cold, and this 

 expansion in the same body is always 

 proportional to some function of the 

 quantity of caloric added or abstracted, 

 yet the absolute expansion or contraction, 

 has been found to differ exceedingly in 

 different bodies. In general, the expan- 

 sion of gaseous bodies is greatest of all ; 

 that of liquids is much smaller ; and that 

 of solids the smallest of all. Thus, 100 

 cubic inches of atmospheric air, by being- 

 heated from the temperature of 32" to 

 that of 212, are increased to 137.5 cubic 

 inches : while the same augmentation of 

 temperature only makes 100 cubic inches 

 of water assume the bulk of 104.5 cubic 

 inches : and 100 cubic inches of iron, 

 when heated from 32 to 212, assume 

 a bulk scarcely exceeding 100.1 cubic 

 inches. From this example, we see that 

 the expansion of air is more than eight 

 times greater than that of water ; and 

 the expansion of water about 45 times 

 greater than that of iron. See EXPAN- 

 SION. 



All substances in nature, as far as we 

 are acquainted with them, occur in one 

 or other of the three following states ; 

 namely, the state of solids, of liquids, or 

 of elastic fluids or vapours. It has been 

 ascertained, that in a vast number of cases, 

 the same substance is capable of exist- 

 ing successively in each of these states. 



