80 
PEOFESSOE KOPP ON THE SPECIFIC HEAT OF SOLID BODIES. 
12. Wcestyn was also of opinion * that the specific heats of the elements remain 
unchanged when they enter into chemical compounds. In 1848 he stated as a general 
proposition ; “ The quantity of heat necessary to raise the temperature of the atomic 
weight of a body through 1° is equal to the sum of the quantities of heat necessary to 
raise the temperature of the atoms, and fractions of atoms, through 1°”. If A is the 
atomic weight and C the specific heat of a compound, a lf a 2 , a 3 ... . the atomic 
weights f, and c z , c 2 , c 3 ... . the specific heats of the elements contained in it, and 
w z , n 2 , n z . . . . the numbers which express how many atoms of each element are con- 
tained in an atom of the compound, then 
AC =n 1 a l c l -\-n 2 a 2 c 2 -\-n z a 3 c z 
As a proof of this law, he compared the calculated values of AC of several compounds 
(metallic iodides and sulphides) and alloys with the observed values, taking Regnault’s 
determinations of the specific heats of the elements and of the compounds. It follows, 
further, from that proposition, that if the formula and the values for several compounds 
are compared with each other, there must be the same differences of the values AC for the 
same differences of formulae. WtESTYN showed by a number of examples that this is so 
approximately. By means of this law, the product of the specific heat and the atomic 
weight for one constituent of a compound may be found, if this is known for the compound 
and the other constituents. Wcestyn deduced in this way the product for oxygen (by 
subtracting from the product for different metallic oxides that found for the metals, 
and from chlorate of potass that for chloride of potassium) to be 2*4 to 2T (0. = 8), 
and for chlorine 3 - 0 to 3’5 (Cl. = 17‘75). Wcestyn finally expressed a doubt 
whether Neumann’s law is universally applicable. He laid stress on the circumstance 
that when two elements give different products, the difference is also met with in the 
products for their analogous compounds ; and, for instance, the greater products which 
mercury and bismuth have in comparison with other elements, are also met with in the 
compounds of these metals. 
13. Garnier (in 1852) developed the viewj, that not only in the case of elements are 
the atomic weights A § inversely proportional to the specific heats C, but that the same 
is the case with water || and solid compounds in whose atom n elementary atoms are 
A 
contained, if the so-called mean atomic weight — be compared with the specific heat C ; 
for elements AxC=3, and for compound bodies ^xC= 3 (if 0=8). He endeavoured 
to prove this from Regnault’s determinations of specific heats. From the latter equa- 
tion he calculated the specific heat for several compounds. In the case of the basic 
oxides, sulphides, chlorides, bromides, and iodides, his calculated results agree tolerably 
* Ann. de Chim. et de Phys. [3] vol. xxiii. p. 295. 
t Wcestyx based bis considerations on Regnatjlt’s thermal atomic weights. 
X Comptes Eendus, vol. xxxy. p. 278. § If Begxault’s thermal atomic weights are taken. 
|| I shall in § 93 return specially to the question how often the specific heat of liquid water was compared 
with that of solid bodies. 
