CALORIC. 



Hfith which a stratum is capable of com- 

 bining, it is clear that caloric cannot pos- 

 sibly be conducted through the body ; 

 that is to say, the strata farthest distant 

 from the source of heat cannot receive 

 any increase of temperature. This limit 

 depends, in all cases, upon the quantity 

 of caloric with which a body is capable 

 of combining before it changes its state. 

 All bodies, as far as we know at present, 

 are capable of combining indefinitely with 

 caloric ; but the greater number, after 

 the addition of a certain number of doses, 

 change their state. Thus ice, after com- 

 bining with a certain quantity of caloric, 

 is changed into water, which is convert- 

 ed in its turn to steam, by the addition of 

 more caloric. Metals, also, when heated 

 to a certain degree, melt, are volatilized, 

 and oxydated; wood and most other com- 

 bustibles catch fire, and are dissipated. 

 As to the rate at which bodies conduct 

 caloric, that depends upon the specific 

 nature of each particular body, the best 

 conductors conducting most rapidly, and 

 to the greatest distance. When bodies 

 are arranged into sets, we may lay it 

 down as a general rule, that the densest 

 set conduct at the greatest rate. Thus 

 the metals conduct at a greater rate than 

 any other bodies. But in considering 

 the individuals of a set, it is not always 

 the densest that conducts best : as bo- 

 dies conduct caloric in consequence of 

 their affinity for it, and as all bodies have 

 an affinity for caloric, it follows as a con- 

 sequence, that all bodies must be con- 

 ductors, unless their conducting power 

 be counteracted by some other pro- 

 perty. 



All solids are conductors ; because all 

 solids are capable of combining with va- 

 rious doses of caloric before they change 

 their state. This is the case in a very re- 

 markable degree with all earthy and 

 Stony bodies : it is the case also with me- 

 tals, with vegetables, and with animal 

 matters. This, however, must be under- 

 stood with certain limitations. All bo- 

 dies are indeed conductors; but they are 

 not conductors in all situations. Most so- 

 lids are conductors at the common tem- 

 perature of the atmosphere ; but when 

 heated to the temperature at which they 

 change their state, they are no longer 

 conductors. Thus, at the temperature 

 of 60, sulphur is a conductor; but when 

 heated to 214, or the point at which it 

 melts or is volatilized, it is no longer a 

 conductor. In the same manner ice con- 

 ducts caloric when at the temperature of 

 20, or any other degree below the freez- 

 ing point; but ice at 32 is not a conduc- 



tor, because the addition of caloric causes 

 it to change its state. 



With respect to liquids and gaseous bo- 

 dies, it would appear at first sight that 

 they also are all conductors ; for they can 

 be heated as well as solids, and heated 

 too considerably without sensibly chang- 

 ing their state. But fluids differ from 

 solids in one essential particular : their 

 particles are at full liberty to jmove 

 among themelves, and they obey the 

 smallest impulse ; while the particles of 

 solids, from the very nature of these bo- 

 dies, are fixed and stationary. One of 

 the changes which caloric produces on 

 bodies is expansion, or increase of bulk ; 

 and this increase is attended with a pro- 

 portional diminution of specific gravity. 

 Therefore, whenever caloric combines 

 with a stratum of particles, the whole 

 stratum becomes specifically lighter than 

 the other particles. This produces no 

 change of situation in solids; but in fluids, 

 if the heated stratum happens to be be- 

 low the other strata, it is pressed up- 

 wards by them, and being at liberty to 

 move, it changes its place, and is buoy- 

 ed up to the surface of the fluid. In 

 fluids, then, it makes a very great dif- 

 ference to what part of the body the 

 source of heat is applied. If it be applied 

 to the kighest stratum of all, or to the 

 surface of the liquid, the caloric can only 

 make its way downwards, as through so- 

 15ds,by the conducting power of the fluid; 

 but if it be applied to the lowest stratum, 

 it makes its way upwards, independently 

 of that conducting power, in consequence 

 of the fluidity of the body, and the ex- 

 pansion of the heated particles. The 

 lowest stratum, as soon as it combines 

 with a dose of caloric, becomes specifical- 

 ly lighter and ascends. New particles 

 approach the source of heat, combine 

 with caloric in their turn, and are displac- 

 ed. In this manner all the particles 

 come, one after another, to the source of 

 heat ; of course the whole of them are 

 heated in a very short time, and the ca- 

 loric is carried almost at once to much 

 greater distances in fluids than in any so- 

 lid whatever. Fluids, therefore, have the 

 property of carrying or transporting ca- 

 loric ; in consequence of which they ac- 

 quire heat independently altogether of 

 any conducting power. 



If we take a bar of iron and a piece 

 of stone of equal dimensions, and put- 

 ting one end of each into the fire, apply 

 either thermometers or our hands to the 

 other, we shall find the extremity of the 

 iron sensibly hot long before that of the 

 stone. Caloric, therefore, is not conduct- 



