120 HEAT OR CALORIC. 



The experiments are commonly made by comparing fluids* or com- 

 minuted solids, after they have been mingled at different tempera- 

 tures. That body which, in a given short time, has lost the greatest 

 number of degrees, has the smallest capacity, and the smallest spe- 

 cific heat, and vice versa. 



The resulting temperature is always nearest to that body, whose 

 capacity or specific heat is the greatest, and therefore the greater the 

 capacity the less the changes of temperature. Boerhaave first dis- 

 covered this remarkable fact, with respect to quicksilver, and water, 

 but Dr. Black first established the law ; many other able men have 

 investigated it, among whom are Wilcke, Irvine, Crawford, Lavoisier, 

 Berard, and Delaroche, Petit, and Dulong, Clement and Des- 

 ormes, &c. 



(c.) Different bodies, whether taken in equal weights, or volumes., 

 contain different quantities of heat or caloric. 



This could never have been known by reasoning a priori; the 

 conclusions are founded entirely upon experiment. 



(d.) Different bodies exposed to the same heating or cooling cause, 

 undergo different changes of temperature, in equal short times, and 

 the capacities are inversely as the change of temperature. Thus fifty 

 spheres, or cubes, equal either in weight or diameter, of as many dif- 

 ferent kinds of matter, if plunged into boiling water, and examined after 

 an interval of five minutes, would be found very differently heated ; or, 

 if already arrived at the temperature of 212, if they were exposed 

 to a freezing air, and examined as above, they would be found very 

 unequally cooled, although in the end, they would in both cases ac- 

 quire a common temperature. 



(e.) In homogeneous bodies, mingled at different temperatures, the 

 resulting temperature is always the arithmetical mean. A pint of 

 water at 100, and a pint at 200, would on being mingled, give 

 150 as the resulting temperature, and the same would be true of 

 any other fluids, or minutely divided solids. 



(/.) In heterogenous bodies, the resulting temperature is never the 

 mean. The capacity of water is 23 that of mercury 1, for the 

 changes which they undergo, when mingled at different temperatures, 

 and in equal weights or volumes, are inversely as the changes the) 

 suffer. 



One pint of mercury at 100 Fahr.+one pint of water at 40,= 

 not 70, the arithmetical mean, but only 60 ; the metal loses 40, 

 which raises the water only 20 ; hence, in equal volumes, water has 

 the greater capacity. If the pint of water be 100, and the mercury 

 at 40, the temperature will be about 80, because the water con- 

 tains more heat than is necessary to raise the mercury to the mean. 



* Always taking it for granted that they do not act chemically on each other. 



