THE EFFECTS OF HEAT. 247 



raise a ton of water from 32° to 174° ; and, on the other hand, when a riso 

 of temperature takes place, the thawing of the ice absorbs a like quantity of 

 heat: thus, in the one case, supplying heat to the atmosphere when the tem- 

 perature falls ; and, in the other, absorbing heat from it when the temperattiro 

 rises. 



In the winter, the weather generally moderates on the fall of snow ; snow 

 is frozen water, and in its formation heat is imparted to the atmosphere, and 

 its temperature increased. 



Steam, on account of the latent heat it contains, is well 

 Why is steam adapted for the warming of buildings, or for cooking. la 

 adapted for passing through a line of pipes, or through meat and vegeta- 

 cookiDgf '""^ ^^^^^ ^* ^ condensed, and imparts to the adjoining surfaces 

 nearly 1000° of the latent heat which it contained before 

 condensation. 



Steam bums much more severely than boiling water, for the reason that 

 the heat it imparts to any surface upon which it is condensed is much greater 

 than that of boiling water. 



Is the quantity ^68. All bodles coiitam incorporated with 

 bod^ief the^'^ them more or less of heat ; but equal weights 

 Bamo? of dissimilar substances, having the same sen- 



sible temperature, contain unequal quantities of heat. 



Thus if we place a pound of water and a pound of mercury 

 be demon- over a fire, it will be found that the mercury will attain to any 

 Btrated? given temperature much quicker than the water. Or if we 



perform the converse of this experiment, and take two equal quantities of 

 mercury and water, and having heated them to the same degree of tempera- 

 ture, allow them to cool freely in the air, it will be found that the water will 

 require much more time to cool down to a common temperature than the 

 mercury. The water obviously contains more heat at the elevated tempera- 

 ture than the mercury, and therefore requires a longer time to cooL 



. . 569. Dissimilar substances require, respectively, different 



meaning of the quantities of heat to raise their temperatures one degree ; and 



term specific ^j^g quantity of heat necessary to produce this effect upon a 



body is termed its specific heat. In like manner, the weight 



which a body includes under a given volume, is termed its specific gravity. 



_ , 570. A substance is said to have a greater 



What IS under- • n ^ t 



stood bycapac- Or Icss capacitv for heat, according as a greater 



ityforheatr .-f r X, J - • A 4- A 



or less quantity of heat is required to produce 

 a definite change of temperature, or an elevation of tem- 

 perature of one degree. 



n d the ^^ general, the capacity of bodies for heat decreases with 



capacity for heat their density. Thus mercury has a less tapacity for heat than 



itanfte vary"?''" '^^tsr, because its density is greater. Air that is rarefied, or 



thin, has a greater capacity for heat than dense air. This 



