SOLIDS, LIQUIDS, AND OASES. 377 



eluded in the permanent list; but Faraday made a serious 

 inroad upon this classification when he liquefied chlorine 

 by cooling and compressing it. Long after this, the gase- 

 ous elements of water, and the chief constituents of air, 

 oxygen, hydrogen, and nitrogen, resisted all efforts to con- 

 dense them; but now they have succumbed to great pres- 

 sure and extreme cooling. 



We thus arrive at a very broad generalization, viz., that 

 all gases are physically similar to steam (I mean, of course, 

 " dry steam," i.e., true invisible steam, and not the cloudy 

 matter to which the name of steam is popularly given), 

 that they are all formed by raising liquids above their boil- 

 ing point, just as steam is formed when we boil water and 

 maintain the steam above the boiling-point of the water. 



But some liquids boil at temperatiires far below that at 

 which others freeze; liquid chlorine boils at a temperature 

 below that of freezing water, and liquid carbonic acid be- 

 low even that of freezing mercury, and liquid hydrogen far 

 lower still. These are cases of boiling, nevertheless, though 

 it seems a paradox according to the ideas we commonly 

 attach to this word. But such ideas are based on our com- 

 mon experience of the properties of our commonest of 

 liquids, viz., water. 



When water boils under the conditions of our ordinary 

 experience, the passage from the liquid to the gaseous state 

 is a sudden leap, with no intermediate state of existence 

 that we are able to perceive; and the conditions upon which 

 water is converted into steam the liquid into the gas 

 while both are at the bottom of our atmospheric ocean, are 

 such as to render an intermediate condition rationally, as 

 well as practically, impossible. 



We find that the expansive energy by which the steam is 

 enabled to resist atmospheric pressure is conferred upon it 

 by its taking into itself, and utilizing for its expansive ef- 

 forts a large amount of calorific energy. When any given 

 quantity of water is converted into steam, under ordinary 

 circumstances, its bulk sudden!}/ becomes above 1700 times 

 greater a cubic inch of water forms about a cubic foot of 

 steam, and nearly 1000 degrees of heat (966'6) disappears 

 as temperature. Otherwise stated, we must give to the cubic 



