EFFECTS OP HEAT. 45 



condensed into the liquid form again, we shall obtain 

 a gallon of boiling hot water, and heat enough will 

 be given out during its condensation to raise seven 

 gallons more of cold water to the boiling point. 



51. The very large proportion of heat which steam 

 therefore contains in this latent state, shows why 

 steam is such an excellent means of conveying heat 

 about from place to place, as in the arrangements 

 for warming buildings, heating coppers, &c. It is 

 quite as hot as so much boiling water, and, in addi- 

 tion, has nearly seven times as much heat thus stored 

 up in the latent form, which becomes sensible, how- 

 ever, as soon as it is condensed. 



52. The general effect of heat upon substances, 

 whether solid, liquid, or gaseous, is to expand or make 

 them larger ; thus whenever we heat a portion of water 

 or any other fluid, it increases in size : upon this fact 

 the construction of the common thermometer depends, 

 which consists of a bulb and tube containing a certain 

 bulk of mercury, or qtiicksilver ; when this is heated 

 it becomes larger, and when cooled, the mercury 

 shrinks, or occupies less space than it did before. 



53. When a substance expands, or becomes larger, 

 it of course becomes lighter. If ten measures are 

 expanded by heat to eleven, it follows that ten mea- 

 sures of the heated substance must weigh one eleventh 

 less than ten measures of it when cold. For example, 

 air, when heated, becomes lighter, and consequently 

 rises, because, becoming larger, it weighs compara- 

 tively, bulk for bulk, less than the cool air around. 



