514 Transactions. 



approximately, the specific heat of gases under constant pressure 

 is inversely proportional to their densities, any dissociation should 

 proportionately increase the specific heat. 



Reasoning similar to the foregoing can be applied to liquids, 

 though with less certainty, and perhaps also to solids. Assum- 

 ing it to be thus applicable, and neglecting the internal-energy 

 factor, the following relations should hold : — 



1. Whenever, in a given mass undergoing chemical change, 

 there is an increase or decrease in the number of molecules, there 

 is a proportionate decrease or increase of the absolute tempera- 

 ture. 



2. The temperature of a given mass may be altered apart 

 from external conditions, thus : (a) by conversion of potential 

 energy of chemical affinity into kinetic energy, and vice versa ; 

 (b) by conversion of internal energy of a molecule into external 

 energy, or vice versa ; (c) by association or dissociation of mole- 

 cules, including ionization ; (d) by dissociation of atoms, as in 

 radium. 



3. The temperature of a given mass remains proportional to 

 the sum total of the kinetic energy of translation of its particles 

 only so long as the number of particles remains constant. 



4. Evolution of heat in a chemical reaction is not necessarily 

 synonymous with production of energy, but may be due merely 

 to the distribution of the original energy amongst a greater or 

 smaller number of molecules. 



The displays of light and heat so familiar in cases of chemical 

 combination suggest the idea that chemical actions take place 

 only when heat is evolved by them. This idea was given definite 

 expression by Thomsen, and later by Berthelot, thus : " Sub- 

 stances which can act chemically upon one another tend, when 

 left freely to their mutual action, to produce that system which 

 is formed with the greatest evolution of heat." This statement, 

 however, has been found to be much too general, and is no longer 

 defended in its entirety, many cases being known in which heat- 

 absorbing reactions occur spontaneously. On examining some 

 of these endothermic reactions, however, it will be found that 

 there is quite a possibility that they are really exothermic after 

 all, so far as the chemical reactions are concerned. Some, if not 

 all, of the apparent loss of heat is obviously due to increase in 

 the number of molecules — e.g., solid Glauber's salt mixed with 

 concentrated hydrochloric acid liquefies spontaneously, and cools 

 down many degrees. On writing the equation a large increase 

 in the number of particles becomes evident — Na 2 S0 4 . 10 H 9 

 + 2 HC1 = 2 NaCl+ H 2 S0 4 + 10 H 2 0. Allowing for ionization, 

 there is an increase of particles in the ratio of about 17 to 5. 

 Hence, even though the transformation be far from complete, 



