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II. A Relation between the Melting-points of the Elements 

 and their Solid Binary Compounds and the Heats of Forma- 

 tion of the latter. By Thomas Carnelley, D.Sc., and 

 L. T. O'Shea, Firth College, Sheffield*. 



THE numerous determinations which have been made by 

 Berthelot and Thomsen of the heat evolved in various 

 chemical reactions have led us to compare the numbers so 

 obtained for the solid halogen compounds of the elements with 

 their melting-points and those of their constituent elements, 

 as it appeared not improbable that some interesting relations 

 might be detected between these physical constants. 



In the present paper are detailed the results which have 

 been obtained by such a comparison. 



(1) In any chemical reaction such as 



Ag 2 + Cl 2 = 2 AgCl + heat evolved, 



the sum of the energies on one side of the equation is equal to 

 the sum of the energies on the other side. The chemical 

 energy of a body is measured by the inverse of the heat ne- 

 cessary to separate the atoms constituting the molecule — or, 

 in the case where the molecule consists of but one atom, of 

 unlocking in that atom the affinities which mutually saturate 

 one another. Therefore the inverse of the heat necessary to 

 separate the two atoms of silver + the inverse of that required 

 to separate the two atoms of chlorine = twice the inverse of 

 the heat required to separate one atom of silver from one atom 

 of chlorine + the heat evolved. 



(2) After many attempts to obtain a numerical measure of 

 the chemical energy of a molecule of any substance, we finally 

 came to the conclusion that it might be approximately repre- 

 sented by the melting-point of the body in such a way that 

 the chemical energy of a molecule of any solid substance is 

 inversely as its melting-point measured from the absolute 

 zero (-273° C). 



Before proceeding further, we wish expressly to state that 

 the inverse of the melting-point of a substance is taken merely 

 as an empirical measure of its chemical energy, because as yet 

 a true measure of it has not been discovered ; and by using it 

 in this way we have been led to the relations given below. 



Assuming, then, tentatively that the inverse of the melting- 



* Communicated by the Authors. 



