410 On Thermodynamic and Metamorphic Functions, &;c. 



peratures have distinct smells by which they can be recognized ; 

 therefore they exist at low temperatures in the gaseous condition : 

 and why, then, not in the perfectly gaseous condition ? And if 

 those metals exist in the perfectly gaseous condition at low tem- 

 peratures, may not other substances chiefly known to us as solids 

 do so, although we cannot smell them ? 



8. Professor Clausius dissents from a statement of mine, that 

 the real specific heat of a substance can be different in the three 

 different states of aggregation — solid, liquid, and gaseous. 

 When differences occur between the apparent values of the spe- 

 cific heat at constant volume of the same substance in those three 

 conditions, he ascribes them to internal work. 



I admit that it is difficult to conceive how the same substance 

 can alter its real specific heat in changing its state of aggregation. 

 But it is also difficult to conceive how the elevation of tempera- 

 ture of liquid water, for example, can be accompanied by internal 

 work to an amount sufficient to account for the excess of the 

 specific heat of liquid water at constant volume above that of 

 steam and above that of ice, those three quantities being nearly 

 as follows : — 



Specific heat at constant volume of ice, about . . . 0*5 

 „ „ liquid water, about 1*0 



„ „ steam .... 0*37 



It appears to me that both difficulties are diminished, if not 

 removed, by supposing that in some cases the same substance, 

 when in different states of aggregation, is not absolutely identical, 

 but isomeric, and may so have different values for its real specific 

 heat. For example, we may suppose that one atom of ice or of 

 steam is composed of two atoms of liquid water ; just as it has 

 been conjectured that an atom of common oxygen may consist of 

 two atoms of ozone; and then a change in the real specific heat 

 becomes a natural result. 



I do not, however, propose that supposition as more than a 

 conjecture ; and for the present I am content to regard as cer- 

 tain merely the fact that the minimum specific heat of the same 

 substance in different states of aggregation is in many cases 

 different, leaving the relation between that minimum specific heat 

 and the real specific heat to be ascertained by further investi- 

 gation. 



Glasgow University, 

 November 15,1865. 



