Relations of Air, Heat, and Cold. 447 



as concentrated sulphuric acid ; sulphuric arid, again, twice 

 as much as glass; and glass itself, tvvic^ as much as silver, 

 and five times as much as mercury. If a pound of water 

 heated 30 degrees be poured into another poinid of water 

 at the temperature of the apartment, the surplus heat will 

 become equally shared between the two masses, the infused 

 portion losing 16^ of its heat, and the recipient gaining 

 15°. But if a pound of mercury heated 30 degrees above 

 the standard be poured into a pound of water; while both, 

 of these now acquire the same temperature, the mercury 

 will lose 29 degrees, and the water gain only one degree. 

 Hence, in the state ot quiescence, mercury contains 29 

 times less heal than vvater, and has its temperature -29 times 

 more attected by equal accessions of that elementary fluid. 

 But even ihe same substance, if its form be mmable, will 

 exhibit similar differences, according to the aspect which it 

 assumes. TIuh, ice is more easily heated than vater, and 

 wafer than steam. The same additioii of heat which would 

 raise the teii.perature of ice lO degrees, would only raise 

 that of watt r 9 degrees, and that of steam 6 degrees. At 

 each stage of iransiti^n, there is hence an apparent pause, 

 attended with a corresponding absorption or evolution of 

 heat. 



"Thus, if a vessel filled with ice be suspended over a steady 

 fire, the ice will continue at the freezing point, till, per- 

 haps in an interval of half an hour, it be entirely melted ; 

 it will then grow regularly warmer, till, after 40 minutes, 

 the water begins to boil : nor will the temperature of the 

 liquid now receive anv further increase, the subsequent ac- 

 cessions of heat being wholly expended in the format'on 

 of the expelled steam, and which would require the space 

 of three hours and a half. In the act of thawing, there- 

 fore, and again in the process of ebullition, there is a suc- 

 cessive absorption of heat, amounting respectively to a dif- 

 ference of temperature in the water of about 73 and 525 

 of the centigrade degrees, or 133 and 943 on Fahrenheit's 

 scale. But the heat thus absorbed is nowise distinguished 

 from the rest, or fitted to perform any different function ; 

 it blends its action and its expansive energies with the ge- 

 neral fluid, and merely serves to restore the equilibrium that 

 had been disturbed by the enlarged capacity, or rather the 

 increased attraction, of ihe mass with which it com- 

 bines." 



'• The gaseous substances are so loosely constituted, that 

 a difference iu their composition is sufficient to alter ma- 

 terially 



