338 



Dr. Kopp on the Specific Heat of Solid Bodies. [May 12, 



and the various metals as elements, chemistry has penetrated to the sam*e 

 depth in that range of inquiry, and has found at the same depth the hmit 

 to its advance. 



But with the proof that this law is not universally true, the conclusion 

 to which this result leads loses its authority. If we start from the ele- 

 ments at present assumed in chemistry, we must admit rather that the 

 magnitude of the atomic heat of a body does not depend on the number of 

 elementary atoms contained in a molecule, or on the complication of its 

 composition, but on the atomic heat of the elementary atoms which enter 

 into its composition. It is possible that a decomposable body may have 

 the same atomic heat as an element. Chlorine might certainly be the 

 peroxide of an unknown element which had the atomic heat of hydrogen ; 

 the atomic heat of peroxide of hydrogen, HO, in the solid state or in 

 solid compounds, must be =2-3 + 4=6'3, agreeing very nearly with the 

 atomic heats of iodine, chlorine, and the elements which follow Dalong and 

 Petit' s law. 



In a very great number of compounds the atomic heat gives more or 

 less accurately a measure for the complication of the composition. And 

 this is also the case with those compounds which, from their chemical 

 deportment, are comparable to the undecomposed bodies. If ammonium 

 or cyanogen had not been decomposed, or could not be by the chemical 

 means at present available, the greater atomic heats of the compounds of 

 these bodies, as compared with analogous potassium or chlorine com- 

 pounds, and the greater atomic heats of ammonium and cyanogen ob- 

 tained by indirect determination, as compared with those of potassium and 

 chlorine, would indicate the compound nature of those so-called compound 

 radicals. The conclusion appears legitimate, that, for the so-called ele- 

 ments, the directly or indirectly determined atomic heats are a measure for 

 the complication of their composition. Carbon and hydrogen, for exam- 

 ple, if not themselves actually simple bodies, are yet simpler compounds 

 of unknown elements than sihcium or oxygen ; and still more complex are 

 the elements which may be considered as following Dulong and Petit' s law. 



It may appear surprising, and even improbable, that so-called elements, 

 which can replace each other in compounds, as for instance hydrogen and 

 the metals, or which enter into isomorphous compounds as corresponding 

 elements, like silicium and tin, should possess unequal atomic heats and 

 unequal complication of composition. But this really is not more sur- 

 prising than that undecomposable bodies and obviously compound bodies, 

 hydrogen and hyponitric acid, or potassium and ammonium, should, with- 

 out altering the chemical character of the compound, replace one another, 

 or even be present in isomorphous compounds as corresponding con- 

 stituents. 



The author concludes his memoir with the following words : — " I have 

 here expressed opinions, in reference to the nature of the so-called ele- 

 ments, which appear to depend upon allowable conclusions from well- 



