HEAT. 



460 grains of the substance, heated to 

 about 12 of Fahrenheit above the sur- 

 rounding air, was suspended in the cen- 

 tre of a vessel which was blackened on 

 the inside, and exhausted of air, to make 

 the cooling slower; the time required 

 being generally about 15 minutes, al 

 though the exhausted vessel was sur- 

 rounded with melting ice. 



The specific heats of metals thus 

 obtained are as under, that of water 

 being considered 100 : 



Bismuth 0.0288 



Lead 0.0293 



Gold 0.0298 



Platinum 0314 



Tin 0.0514 



Silver 0.0557 



Zinc 0.0927 



Tellurium 0.0912 



Copper 0.0949 



Nickel 0.1035 



Iron 0.1100 



Cobalt 0.1498 



Sulphur 0.1880 



From the statements which have been 

 made respecting the capacities of bodies 

 for heat, and the specific heat of bodies, 

 it will be evident that a very close con- 

 nection exists between these, so close, 

 that one of the terms is frequently used 

 for the other without occasioning con- 

 fusion: the former means the relative 

 powers of bodies in receiving and retain- 

 ing heat in being raised to any given 

 temperature, some bodies receiving and 

 retaining much more than others ; the 

 latter term applies to the actual quanti- 

 ties of heat so received and retained. 



Whatever may be the cause of the 

 different capacities of bodies for heat, 

 it appears to be greatly influenced by 

 the state of density in which bodies 

 exist ; although not so regularly as to 

 admit of being considered as an inva- 

 riable relation: hydrogen, the lightest 

 of all bodies, having the greatest capa- 

 city, and metals, the heaviest of bodies, 

 having the least. The same body may 

 have its capacity enlarged by the de- 

 crease of its density ; thus, the intense 

 cold existing in the higher regions of 

 the atmosphere has been accounted for 

 on the supposition of the increased ca- 

 pacity of the ah- for heat. On the contra- 

 ry, by increasing the density of a body, its 

 capacity for heat is diminished ; a quan- 

 tity of heat is therefore set free, and pro- 

 duces sensible effects ; as in the sudden 

 condensation of air, the rapid reduction 

 of which to one-fifth of its volume occa- 

 sions the evolution of heat in sufficient 



quantity to inflame tinder ; and if the 

 condensation be effected in a glass tube 

 in a dark place, a flash of light may be 

 seen at the same time. 



Supposing caloric to consist of mate- 

 rial particles, the tendency of which is 

 to diffuse themselves equally over space, 

 it seems natural that they should be 

 introduced in largest quantity into 

 those bodies, the particles of which 

 are at the greatest distance from 

 each other. On this account, bodies 

 which have the least density may have 

 the greatest capacity for heat ; and, as 

 the particles of different bodies probably 

 attract heat with different degrees of 

 force, which, it is imagined, may ac- 

 count for the different quantities of 

 heat retained by different bodies at any* 

 given temperature; although by this 

 attraction no intimate union be occa- 

 sioned as if chemical attraction were 

 exerted, the particles of heat still retain- 

 ing all their properties unaltered. 



CHAPTER VIII. 



Of the absolute quantity of Heat which 

 any Body contains at any given Tem- 

 perature. 



ALL bodies, it is obvious, must contain 

 limited quantities of heat ; but since it is 

 not in our power to deprive them of it 

 entirely, it is exceedingly difficult to de- 

 termine how much any body continues 

 to possess after we have reduced its 

 temperature as much as possible. While 

 Dr. Irvine was engaged in the investi- 

 gation of the capacities of bodies for 

 heat, it occurred to him, that, if the 

 quantities of heat contained in bodies 

 be in proportion to their capacities, a 

 knowledge of the capacity of a body in 

 its different states, together with the 

 quantities of heat which it absorbs or 

 gives out when it undergoes a change 

 of form, may enable us to infer the 

 amount of the whole quantity existing 

 in the body : as for example, the capa- 

 city of water to that of ice being as 

 1 to 9. Water at the temperature of 

 32 will contain one-tenth more heat 

 than ice at the same temperature. Be- 

 fore ice can assume the state of water, 

 it must give out this tenth part, which 

 may then be measured. Dr. Black esti- 

 mated the quantity at 140 of Fahren- 

 heit, that is to say, ice requires as much 

 heat to liquefy it as would raise the 

 temperature of the same weight of wa- 



