1864.] Dr. Kopp on the Specific Heat of Solid Bodies. 231 



The atomic heats of many elements * are, in accordance with this law, 

 approximately equal ; they vary between 6 and 6*8, the average being 

 about 6*4. The explanations attempted why this law only approximately 

 holds good, he considers inadequate. In any case there are individual 

 elements which do not obey this law. The atomic heat of phosphorus, for 

 instance, as deduced from direct determinations of its specific heat in the 

 solid state, is considerably smaller (about 5 '4) ; and still more so are those 

 of silicium (about 4), of boron (about 2-7), and of carbon (1*8 for dia- 

 mond). 



A regularity, to which attention has been already drawn, is, that the 



quotient obtained by dividing the atomic heat of a compound by the 



number of elementary atoms in one molecule, is approximately equal to 



C*4 ; equal, that is, to the atomic heat of an element according to Dulong 



and Petit' s law. Thus the atomic heat of the chlorides R CI and E CI has 



been found to be 12*8 on the average, and of the chlorides R Cl2=18*5. 



12*8 18*5 

 Now ^ = 6*4, and _ = 6*2. The same regularity is met with in 



metallic bromides, iodides, and arsenides ; and, according to the author's 

 determinations, it is even found in the case of compounds which contain as 

 many as seven, and even of nine elementary atoms. The atomic heat of 



Zn CI, is 43*4, and that of ^t Cl^ is 55*2 ; now 1|^=6*2 and 



55*2 



-^^=6*1. But the author shows at the same time that this regularity 



is far from being general. For the oxides of the metals the quotient is less 



than six, and is smaller the greater the number of atoms of oxygen in the 



oxide. (From the average determinations of the atomic heats, it is for the 



11*1 27*2 

 metallic oxides RO^=-——= 5*6 ; for the oxides R2O3 and Rg^s — — - 



=5*4; for the oxides R 0^= =4*6.) The quotient is still smaller for 



o 



compounds which contain boron as well as oxygen (for instance, it is 



1^=4*2 for the borates, R B O3 ; it is i^=3*3 for boracic acid, B^Og), 

 4 5 



11*3 



or which contain siHcium (for silicic acid, SiOg, it is — ^ = 3*8),orhydro- 

 ^J 



8'6 



gen (for ice, HgO, it is — =2*9), or, finally, which contain carbon and hy- 



3 



36*9 



drogen as well as oxygen (for succinic acid, Hg O,, for instance, it is 



= 2*6). It maybe stated in a few words, in what cases this quotient 

 approximates to the atomic heat of most of the elements, and in what 



* In accordance with recent assumptions for the atomic weights, H==l; Cl=35-5; 

 = 16; S = 32; B=10-9;€=12; Si = 28. E, stands for a monequivalent atom, e. 5'. 

 As = 75; Na = 23; K = 39*l; Ag = 100; B signifies a polyequivalent atom, 5'. ^a= 40 ; 

 Pb=207; Fe=56j Go = 63*4; €r=52*2; i»t=184,&c. 



