378 SCIENCE IN SHORT CHAPTERS. 



inch of water at 212 as much heat as would raise it to a 

 temperature of 212 plus 966*6, or 1,178 -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 tempera- 

 ture, is otherwise occupied. Its energy ia partly devoted to 

 the work of increasing the bulk of the water to the above- 

 named extent, and partly in conferring on the steam its 

 gaseous specialty that is, in overcoming 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 func- 

 tions 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 chemi- 

 cal energy, which hold their elements together, are weaker 

 than the cohesion which binds and holds them in the con- 

 dition of solid or liquid, and are more easily broken by the 

 expansive energy of heat. 



To illustrate this, let us take two common and well- 

 known oils olive oil and turpentine. The first belongs to 

 the class of " fixed oils," and second to the "volatile oils." 

 If we apply heat to liquid turpentine, it boils, passes into 

 the state of gaseous turpentine, which is easily condensible 

 by cooling it. If the liquid result of this condensation is 

 examined, we find it to be turpentine as before. Not so 

 with the olive oil. Just as this reaches its boiling point, 



