186 
PROFESSOR KOPP ON THE SPECIFIC HEAT OF SOLID BODIES. 
milarity of chemical character. That that, which may be supposed and expressed by the 
so-called rational formula in reference to the internal constitution of compounds, does 
not affect the atomic heat, becomes more probable from the fact that chemically similar, 
and even isomorphous compounds, one of which contains an atomic group in the place 
of an individual atom in the other, exhibit dissimilar atomic heats. This is seen, for 
instance, in comparing analogous chlorine and cyanogen compounds (Cy=CN); the 
latter have far greater atomic heats. Thus the atomic heat 
Of chloride of mercury, HgCl 2 , § 84, is 18'0 
„ cyanide of mercury, Hg Cy 2 , § 89 25'2 
„ chloride of zinc and potassium, Zn K 2 Cl 4 , § 84 43’4 
„ cyanide of zinc and potassium, Zn K 2 Cy 4 , §89 . . . . . . . 59 '6 
In like manner ammonium compounds (Am=N H 4 ) have atomic heats considerably 
greater than the corresponding potassium compounds. This is seen from the following 
Table : — 
Chloride of potassium, K Cl, § 84 M 12’9 
„ ammonium, Am Cl, § 84 20-0 
Nitrate of potass, KN 0 3 , § 88 M 23*5 
„ ammonia, Am N 0 3 , § 88 36*4 
Sulphate of potass, K 2 Sq 4 , §87 M 336 
„ ammonia, Am 2 Sq 4 , § 87 46-2 
97. That undecomposable atoms and atomic groups are contained in compounds with 
the atomic heats they have in the free state is further probable from the fact that the 
sum of the atomic heats of such atoms, or atomic groups, as when united form a certain 
compound, is equal or approximately equal to the atomic heat of this compound. For 
many compounds whose elements obey Dulong and Petit’s law, what has been stated 
in § 93 contains the proof that the atomic heat of these compounds is equal to the sum 
of the atomic heats of the elementary atoms contained in one atom of the compounds. 
That this is also observed when atomic groups are supposed to be united, forming 
more complicated compounds, will be seen by bringing forward a few examples. The 
atomic heat has been found 
For the oxides, BO, enumerated in § 85 M 11T 
„ sesquioxide of iron, Fe 2 0 3 , § 85 M 26*8 
Sum for Fe 2 R0 4 . . . 37-9 
„ magnetic iron ore, Fe 3 0 4 , § 85 M 37*7 
„ the oxides, B0, in § 85 M 11T 
„ the acids, R 0 3 , in § 85, according to Regnault .... M 18 - 8 
Sum for R R 0 4 . . . 29-9 
„ chromate of lead, Pb0r0 4 , §87 29’0 
