403 Prof. R. Clausius on the Second Fundamental 



chemical compounds into their elements. In all these cases the 

 effect of the heat consists in loosening- or completely dissolving 

 the connexion which exists between the molecules or atoms, and 

 in separating to the greatest possible distance such molecules as 

 are already completely disconnected from each other. 



In order to be able to express this action shortly, I have in- 

 troduced a magnitude which denotes the extent to which this 

 separation and parting of its smallest particles, which it is the 

 tendency of heat to effect, has already been carried in the case 

 of any body. This magnitude I call the Disgrcgation of the body. 

 The disgrcgation of a body is consequently, among the three states 

 of aggregation, least in the solid state, greater in the liquid state, 

 and greatest of all in the gaseous state. In the last condition 

 it can still be increased by the molecules separating further from 

 each other — that is, by the gas expanding to a larger volume. 

 In like manner, the decomposition of a chemically compound 

 body into its elements is in general accompanied by an increase 

 of disgrcgation. 



By help of this conception the. effect of heat can be simply ex- 

 pressed by saying that heat tends to increase the disgregation of 

 bodies. 



But in order that the disgregation of a body may be increased, 

 resistances must in most cases be] overcome, and resistances of 

 two different lands. In the first place, in order partially or 

 completely to destroy the connexion between the molecules, the 

 forces with which the molecules mutually attract each other must 

 be overcome ; and in the second place, there are commonly, in 

 addition to these internal forces, other external forces which act 

 upon the body from without. Thus, for example, in order that 

 a body subject to external pressure may expand, this pressure, 

 which opposes an increase of volume, must be overcome. Ac- 

 cordingly heat, when it causes increase of disgregation, must 

 perform internal and external ergon in overcoming the opposing 

 forces. In the performance of this ergon, heat is used up ; and 

 thus the increase of disgregation invoices conversion of heat into 

 ergon. Conversely, in order to diminish disgregation, ergon (and 

 in general both internal and external ergon) must be expended; 

 since the forces which in the former case were overcome by heat 

 must now in their turn overcome it. In this process heat is pro- 

 duced ; and we consequently arrive at the result that, when dis- 

 gregation is diminished, ergon is transformed into heat. 



For a reason which shall be discussed further on, we will as- 

 sume provisionally that all the changes we are considering take 

 place in such a way that the inverse changes can take place under 

 exactly the same circumstauces. Such changes as these we will, 

 for shortness, call reversible changes. This limitation being pre- 



