76 
PROFESSOR KOPP ON THE SPECIFIC HEAT OF SOLID BODIES. 
tellurium, cadmium, and silver for instance) atomic weights are taken which differ from 
those of Berzelius. In the case of the sulphides, the specific heats may be calculated 
from those of the constituents, assuming that the specific heats of the elements in these 
compounds are the same as in the free state. The same holds good for several 
chlorides and for basic metallic oxides, if the specific heats of chlorine and of oxygen, 
as given by the above formula, are taken as basis. But in acids a smaller specific heat 
must be taken for oxygen (one half in several acids and null in phosphoric acid) ; and 
there are even compounds (cassiterite, e. g., or arsenious acid), in which the same element 
is contained partly with the normal and partly with the modified specific heat* * * § . For 
oxygen salts it is to be assumed that both the acid and the base have the same specific 
heat as in the free state, and hence the specific heat of one constituent (of the acid, for 
instance) may be calculated, if that of the salt and that of the other constituent (the 
base) is known ; and it is also found that the specific heat of chromic acid in the neu- 
tral and in acid chromate of lead is the same. 
This memoir of Hermann’s did not become much known. Unacquainted with it, 
other philosophers have subsequently developed independently similar opinions. 
7. In 1835 Rudberg described a method j*, which, by ascertaining the heat developed 
when salts are dissolved in water, in experiments in which the proportion of the salt 
to the water was constant, but the temperature of the salt varied, should give a means of 
at once determining the specific heat of the salt, and of the heat which was either absorbed 
or became free. Yet the numbers which he obtained from his experiments for the 
specific heat of solid salts are undoubtedly erroneous. 
Dumas $ (in 1838) discussed the possibility of determining the specific heat of organic 
bodies by the following process. A platinum vessel containing the substance in ques- 
tion, along with a thermometer, is to be heated to 30° or 40°, and then brought into a 
vessel provided with a second thermometer, and containing water, the temperature 
being about 5° or 6° lower than that of the surrounding room. When the temperature 
has risen to the same extent above that of the room, both thermometers are to be 
observed. I know no determinations made by this method. 
8. In 1840 Regnault commenced the publication of a series of important investiga- 
tions on specific heat which he had made. As they are generally known, I may be 
more brief in enumerating the contents of the individual publications. In the first 
which he published, Regnault developed § the reasons which led him to prefer the 
method of mixture to other processes for determining the specific heats of solid bodies ; 
* Hermann designates such compounds as hermaphrodites. He thinks that an acid and a base may have the 
same composition, and that they may form salts with each other. Cassiterite, for instance, he considers to be 
stannate of binoxide of tin. 
f Berzelius’s ‘ Jahresbericht,’ vol. xv. p. 63. Poggendorff’s ‘Annalen’, vol. xxxv. p. 474. 
J Dumas’s “ These sur la question de Faction du calorique sur les corps organiques” (Paris, 1838) Ann. 
der Pharm. und Chem. vol. xxviii. p. 151. 
§ Ann. de Chim. et de Phys. [2] vol. lxxiii. p. 5. 
