1S13.] Specific Heat of the different Gases. 437 



of state, leads one to believe, if the opinion of Irvine on the 

 subject be adopted, that the capacity of vapours fur heat is much 

 greater than that of the corresponding liquids. The solution of 

 this question would probably be the most certain means of 

 throwing light on this important subject. Unfortunately, out 

 experiments are very few, owing to the great difficulty of this 

 kind of research. We have confined ourselves solely to the 

 vapour of water, nor have we determined its specific heat with 

 the utmost precision. Our experiments lead to the conclusion, 

 as will be seen in the preceding table, that the specific heat of 

 vapour is 0*847, that of water being 1-000. It would be neces- 

 sary to conclude from it, that the specific heat of water, so far 

 from increasing when it passes into vapour, undergoes a diminu- 

 tion. This would be sufficient to overturn the whole doctiineof 

 Irvine. This conclusion would be similar to that which we have 

 drawn in the following paragraph, with infinitely more certainty, 

 relative to the heat disengaged, or absorbed, during the combi- 

 nations of bodies We acknowledge, however, that though we 

 consider our determination of the specific heat of vapour as not 

 far from the truth, we have not such an entire confidence in it, 

 as to draw from it a conclusion of such importance without 

 hesitation. 



§ V. — Specific Heat of the Gases compared with that of the 

 Compounds into which they enter. 



When during the combination of two bodies there take place 

 a condensation and a disengagement of heat, the compound has 

 a smaller specific heat than that which we should obtain by a 

 calculation founded on the specific heats of the two constituents. 

 When, on the other hand, there is a production of cold, the 

 compound has a greater specific heat than is indicated by calcu- 

 lation.* This, at least, is the result of almost all the experi- 

 ments hitherto made on the subject. Two facts only are known 

 to constitute an exception to this general law : and we may very 

 well suppose, that both are owing to some error in the observa- 

 tion. They were both observed by Lavoisier and de Laplace; 

 the one on the combination of lime with water, the other in the 

 solution of nitre in water. 



Dr. Irvine, of Glasgow, the first discoverer of this law, and 

 who was unacquainted with the two facts above stated, deduced 

 from it a very ingenious hypothesis, by means of which lie 

 explained the disengagement of heat which takes place in com- 

 binations. He supposes that this disengagement is entirely due 



* Tbli calculation ii »en iimple< Let 1 ')•• the mats of in* compound, a 

 "in- of iii conalilaenUj I - «, the other; e, the specify heal of ibe Brit cou- 

 nitocnt) <l, that of Ibe second. The ipecific heat of the componnd is a i » 

 (I - a) d. 



