Dr. Woods on the Heat of Chemical Combination. 301 



of specific heat in the solid and liquid state, and L the latent 

 heat. Now as Dulong and Petit show that the atomic weight 

 is as the specific heat, we may substitute one for the other, 

 and in the formula call the specific heat a; and as the spe- 

 cific heat increases with the expansion, in different states of a 

 body it will be inversely as the specific gravity, or nearly so. 

 Therefore we may say that the specific heat of a body in the 



solid and liquid state may be called -j and -, where s and s' re- 

 present the specific gravity of the solid and liquid respectively. 



Then the S of Person's formula may be replaced by -j . But 



s 1 is s divided by the expansion of the body from the solid to the 

 liquid state ; and as we are taking L (or the latent heat) to re- 



ft Lrt 



present that quantity, therefore — = -, or — . Using this in 



the formula, we get L 



(160 + x ^ - a - =L, or (160 + /) x j = j^. 



But as the greater j — r- is, — and consequently - which re- 

 presents the atomic volume — the less L is ; therefore for a given 

 temperature connected with the fusing-point, the greater the expan- 

 sion from the solid to the liquid state the less is the atomic volume. 

 If in the change from a solid to a liquid state the amount of 

 expansion were only due to atomic movement, that is, if crystal- 

 lization or other structural arrangements did not cause masses to 

 change relative places, L or the latent heat, and the expansion 

 would be equal, as in the case of liquids becoming vapours ; but 

 on account of these arrangements, L and the expansion can be 

 only approximations. Therefore in the subjoined table, where 



L is calculated by means of the formula (160 + /) x — = j _, , 



it is not meant to give the latent heat accurately, but merely to 

 show that the principle of the substitution used above is correct. 

 The number;; representing the latent heat are taken from Per- 

 son's paper, as are also the fusiug-points j the atomic volumes 

 from 1'layl'air and Joule's memoir published in the Transactions 

 of the Chemical Society. 



