SOLIDS, LIQUIDS, AND GASES. 301 



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 boiling-point, just as steam is formed when we 

 boil water and maintain the steam above the boiling-point o the 

 water. 



But some liquids boil at temperatures far below that at which 

 others freeze ; liquid chlorine boils at a temperature below that of 

 freezing water, liquid carbonic acid below even that of freezing mer- 

 cury, and liquid hydrogen far lower still. These are cases of boil- 

 ing, nevertheless, though it seems a paradox according to the ideas 

 we commonly attach to this word. But such ideas are based on 

 our common 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 efforts, a large amount of calor- 

 ific energy. When any given quantity of water is converted into 

 steam, under ordinary circumstances, its bulk suddenly 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 tempera- 

 ture. Otherwise stated, we must give to the cubic inch of water at 

 212 as much heat as would raise it to a temperature of 212 plus 

 966-6 or 1178-6 if it remained liquid. This is about the temperature 

 of the glowing coals of a common fire ; but the steam that has thus 

 taken enough heat to make the water red hot is still at 212 no hotter 

 than the water was while boiling. 



This heat, which thus ceases to exhibit itself as temperature, is 

 otherwise occupied. Its energy is partly devoted to the work of in- 

 creasing the bulk of the water to the above-named extent, and partly 

 in conferring on the steam its gaseous speciality that is, in over- 

 coming liquid cohesion, and substituting for it the opposite property 

 of internal repulsive energy which is characteristic of gases. My 

 reasons for thus defining and separating these two functions of the 

 so-called " latent' ' heat will be seen when we come to the philosophy 

 of the interesting researches of Dr. Andrews. 



As already explained, all gases are now proved to be analogous to 

 steam ; they are matter expanded and rendered self-repulsive by 

 heat. All elementary matter may exist in either of the three forms 

 solid, liquid, or gas, according to the amount of heat and pressure to 

 which it is subjected. I limit this wide generalization to elementary 

 substances for the following reasons. 



Many compounds are made up of elements so feebly held together 

 that they become " dissociated " when heated to a temperature below 

 their boiling-point. Or their condition may be otherwise defined by 

 stating that the bonds of chemical energy, which hold their elements 

 together, are weaker than the cohesion which binds and holds them 



