82 
PEOFESSOE KOPP ON THE SPECIFIC HEAT OF SOLID BODIES. 
salts, that their specific heats may be calculated in close approximation with those found 
experimentally on the assumption that the constituents, anhydrous salt and water con- 
sidered as ice, have the same specific heats in them as in the free state. By the same 
method, Alluard* (in 1859) determined the specific heat of napthalene. ScHAFARixf, 
lastly, has executed by the method of mixtures a series of experiments on the determi- 
nation of the specific heats of vanadic, molybdic, and arsenious acids. 
Quite recently (1863), PapeJ has published investigations on the specific heat of anhy- 
drous and hydrated sulphates. He worked by the method of mixture, which he mo- 
dified in the case of salts rich in water, by placing them in turpentine, and observing 
the increase of temperature produced in the salt and in the liquid by immersing heated 
copper. As a more general result, Pape finds that for hydrated sulphates of analogous 
formulse, the products of the specific heats and the equivalents are approximately 
equal; and further, that with sulphates containing different quantities of water, the 
product of the specific heat and the equivalent increases with the quantity of water, 
in sueh a manner, that to an increase of each one equivalent there is a corresponding 
increase in the product. 
15. In the preceding paragraphs I have collated, as far as I know them, the investiga- 
tions on the specific heat of solid bodies, on the relations of this property to the atomic 
weight, and on the connexion with the chemical composition of a substance. The views 
which have been expressed relative to the validity of Dulong and Petit’s § and of 
Neumann’s laws, and also as to the question whether the elements enter into chemical 
compounds with the same specific heats which they have in the free state or with modi- 
fied ones, have been various and often discordant. In this respect it may be difficult to 
express an opinion which has not been already either stated or hinted at, or which at 
any rate cannot be naturally deduced from a view previously expressed. 
The results to which my investigations on the specific heats of solid bodies have led 
me are the following : — Each solid substance, at a sufficient distance from its melting- 
point, has a specific heat, which may vary somewhat Avith physical conditions (tempe- 
rature, greater or less density, amorphous or crystalline conditions, &c) ; yet the variations 
are never so great as must be the case if a variation in the specific heat of a body is to 
the specific heat of crystallized borax and of ordinary phosphate of soda. He has subsequently published the results 
of his experiments for the latter salt (Ann. de Chim. et de Phys. [3] vol. xxvii. p. 253), hut I cannot find the 
number which he found for crystallized borax. * Ann. de Chim. et de Phys. [3] vol. lvii. p. 438. 
t Berichte der Wiener Akademie der Wissenschaften, vol. xlvii. p. 248. 
X Poggendorff’s ‘ Annalen,’ vol. cxx. pp. 337 & 579. 
§ The universal validity of this law was also defended by Brehow, “ On the relation of the Specific Heat to 
the Chemical Combining Weight.” Berlin, 1838. I only know this paper from the mention of it in the new 
edition of Gehler’s * Physicalisches Worterbuch,’ vol. x. p. 818. It is also admitted by Manx, in his attempt to 
deduce this law from the undulatory theory of heat. (1857 : Schxomixch and Witzschel’s 4 Zeitschrift fur 
Mathematik und Physik,’ II. Jahrgang, p. 280) ; and by Stefan, in his investigation on the bearing of this 
law on the mechanical theory of heat (1859 : Berichte der Wiener Akademie, vol. xxxvi. p. 85). 
