1864.] Dr. Kopp on the Specific Heat of Solid Bodies, 233 



And it is not less surprising that arseniate of potass, K As O3, and chlorate 

 of potass have the same atomic heat as sesquioxide of iron, Fe^ O3, or ar- 

 senious acid, ASg O3 : with very different characters these compounds have 

 approximately equal atomic heat. 



But comparability of chemical compounds, as regards the atomic heat, 

 is not limited to the cases in which, as far as can be judged, the individual 

 atoms have analogous construction. We do not regard the atom of binoxide 

 of tin or of titanic acid as analogous in construction to the atom of tung- 

 state of lime or of chromate of lead ; nor to nitrate of baryta, or metaphos- 

 phate of lime. But if the formulae of those binoxides are doubled or 

 tripled, they may be compared with these salts, and their atomic heats are 

 then approximately equal, as is^the case for compounds of analogous 

 chemical character. The atomic heats are for — 



Binoxide of tin 



2SnO, 



= Sn,0, 



27-6 



Titanic acid 



2TiO. 





27-3 



Tungstate of lime .... 





.€a=^0. 



27-9 







Pb€rO, 



29-0 



Permanganate of potass . 





KMnO, 



28-3 



Perchlorate of potass . . . 





. KCIO, 



26-3 





. ,3SnO, 



= Sn3 0e 



41-4 





..3TiO, 



= ^13^6 



41-0 



Nitrate of baryta 





■ BaN.O, 



38-9 



Metaphosphate of lime 





..€a?,0. 



39-4 



These results seem to give to Neumann's law a validity far beyond the 

 limits to which it had hitherto been considered to apply. But, on the 

 other hand, the author's comparisons go to show that neither Neumann's 

 nor Dulong and Petit' s law is universally valid. 



Neumann's law is only approximate, as is well known. For such analo- 

 gous compounds as, from what we know at present, are quite comparable 

 and, in accordance with this law, ought to have equal atomic heats, Kegnault 

 found the atomic heats differing from each other by to ^. In a few 

 such cases there are even greater differences in the atomic heats, for which 

 an adequate explanation is still wanting. 



But there are other differences in the atomic heats of some compounds 

 which might have been expected to have equality of atomic heat in accord- 

 ance with Neumann's law — differences which occur with regularity, and 

 for which an explanation is possible. Certain elements impress upon all 

 their compounds the common character that their atomic heats are smaller 

 than those of analogous compounds of other elements. This is the case, for 

 instance, with the compounds of boron : the atomic heat of boracic acid is 

 much less than that of the metalHc oxides O3 and ^3 5 atomic heat 

 of the borates R B is much less than that of the oxides R^ 0^= (2 R O) ; 

 and the atomic heat of borate of lead, Pb B^ O^, is far less than that of mag- 

 netic oxide of iron, J^Cg O^. The same is the case with compounds of carbon, 

 if the alkaline carbonates, Rg € O3, are compared with the metallic oxides 

 R3 O, = (3 R O), or the carbonates R € O, with the metalUc oxides R^ O3 and 



