134 HELMllOLTZ ON THE CONSERVATION OP FORCE. 



itself; this description of motion seems to be similar to the con- 

 duction of heat. It is also clear, that such motions in the atoms 

 may cause changes in the molecular forces, and consequently give 

 rise to expansion or an alteration of the state of aggregation. Of 

 what nature the motion is, we have no means whatever of ascer- 

 taining ; the possibility of conceiving the phsenomena of heat as 

 being due to motion is, however, sufficient for our present object. 

 The conservation of force in the case of these motions will hold 

 good in all cases where hitherto the conservation of caloric has 

 been assumed ; for example, in all phaenomena of radiation and 

 conduction of heat from one body to another, and in the case of 

 the appearance and disappearance of heat during changes of 

 aggregation. 



Of the different modes in which heat manifests itself, we have 

 considered the cases where one body radiates into another, and 

 where it is produced by mechanical force ; further on we will 

 examine the heat generated by electricity. It remains to con- 

 sider the development of heat in chemical processes. It has 

 been heretofore referred to the setting free of caloric which was 

 previously latent in the combining bodies. According to this, 

 we must ascribe to every simple body, and every chemical com- 

 bination which is capable of entering into still further combi- 

 nations of a higher order, a definite quantity of latent heat which 

 is necessary to its chemical constitution. From this we derive 

 the law, which has been also partially verified by experience, 

 that when several bodies unite together to a chemical com- 

 pound, the same quantity of heat is developed, no matter in what 

 order the combination may have been effected*. According to 

 our way of viewing the subject, the quantity of heat developed 

 by chemical processes would be the quantity of vis viva produced 

 by the chemical attractions, and the above law would be the 

 expression for the principle of the conservation of force in 

 this case. 



As little as the conditions and laws of the generation of heat 

 have been investigated, although such a generation undoubtedly 

 occurs, this has been done with reference to the disappearance 

 of heat. . Hitherto we are only acquainted with cases in which 

 chemical combinations have been decomposed, or less dense 



* Hess, in Pogg. .^ww. vol. 1. 392 ; Ivi. 598. 



