1864.] Dr. Kopp on the Specific Heat of Solid Bodies. 237 



It might here appear doubtful whether calculation was not refuted by- 

 experiment. The discrepancy was removed by the observation that the 

 substance is distinctly more viscous at 50° than it is at lower temperatures, 

 and by the suspicion that it might at 50° (that is, 100° below its melting- 

 point) already absorb some of its latent heat of vitreous fusion. This was 

 found to be the case ; two concordant series of experiments gave as the 

 mean of the specific heat the numbers : 



Between 18° and 37° 0*178 



Between 18° and 43° 0*194 



Between 18° and 50° 0*277 



The first two numbers differ so little that it may be supposed the number 

 found for temperatures below 37° is very near the true specific heat of this 

 compound ; it also agrees well with the calculated number. 



In the sixth part the author enters into considerations on the nature of 

 the chemical elements. 



He calls to mind the discrepancy which has prevailed, and still prevails, 

 in reference to certain bodies, between their actual indecomposability, and 

 the considerations, based on analogy, according to which they were held to 

 be compound. Even after Davy had long proclaimed the elementary 

 nature of chlorine, it was maintained that it contained oxygen. In regard 

 both to that substance and to bromine and iodine, the view that they are 

 peroxides of unknown elements still finds defenders. That iodine, by a 

 direct determination of specific heat, and chlorine, by indirect deduction, 

 are found to have an atomic heat in accordance with Dulong and Petit's 

 law, puts out of doubt that iodine and chlorine, if compound at all, are 

 not more so than the other elements to which this law is considered to 

 apply. 



According to Dulong and Petit' s law, compounds of analogous atomic 

 composition have approximately equal atomic heats. In general, com- 

 pounds whose atom consists of a larger number of undecomposable atoms, 

 or is of more complex constitution, have greater atomic heat. Especially 

 in those compounds all of whose elements follow Dulong and Petit's law, 

 is the magnitude of the atomic heat a measure of the complication, or of 

 the degree of complication. If Dulong and Petit's law were universally 

 valid, it might be concluded with great certainty that the so-called ele- 

 ments, if they are really compounds of unknown simpler substances, are 

 compounds of the same order. It would be a remarkable result, if the 

 art of chemical decomposition had everywhere reached its limits at such 

 bodies as, if at all compound, have the same degree of composition. 

 Let us imagine the simplest bodies, perhaps as yet unknown to us, the true 

 chemical elements, to form a horizontal layer, and above them to be 

 arranged the more simple and then the more complicated compounds ; the 

 general^validity of Dulong and Petit's law would include the proof that 

 all the elements at present assumed to be such by chemists lay in the 

 same layer, and that, in admitting hydrogen, oxygen, sulphur, chlorine. 



