THE VALENCY AND SPECIFIC HEAT O.F THE METALS 687 



multiplying the specific heats found by experiment by the correspond- 

 ing atomic weights we obtain the following figures : Li, 6-59, Na, 6*75 

 and K, 6 '47. Of the alkaline earth metals the specific heats have been 

 determined : of magnesium = 0-245 (Regnault and Kopp), of calcium 

 = 0-170 (Bunsen), and of barium = 0-05 (Mendele*eff;. If the same 

 composition be ascribed to the compounds of magnesium as to the 

 corresponding compounds of potassium, then the equivalent of mag^ 

 nesium will be equal to 12. On multiplying this atomic weight by the 

 specific heat of magnesium, we obtain a figure 2-94, which is half that 

 which is given by the other solid elements and therefore the atomic 

 weight of magnesium must be taken as equal to 24 and not to 12. 

 Then the atomic heat of magnesium = 24 x 0*245 5*9 ; for calcium, 

 giving its compounds a composition CaX 2 for example CaCl 2 , CaSO 4 , 

 CaO (Ca = 40) we obtain an atomic heat = 40 x 0-17 = 6-8, and for 

 barium it is equal to 137 x 0-05 = 6 -8 ; that is, they must be counted 

 as bivalent, or that their atom replaces H 2 , Na 2 , or K 2 . This con- 

 clusion may be confirmed by a method of analogy, as we shall afterwards 

 see. The application of the principle of specific heats to the determi- 

 nation of the magnitudes of the atomic weights of those metals, the 

 magnitude of whose atomic weights could not be determined by 

 Avogadro-Gerhardt's law, was made about 1860 by the Italian pro- 

 .fessor Cannizzaro. 



Exactly the same conclusions respecting the bi valence of magnesium 

 and its analogues are obtained by comparing the specific heats of their 

 compounds, especially of the halogen compounds as the most simple, 

 with the specific heats of the corresponding alkali compounds. Thus, 

 for instance, the specific heats of magnesium and Qalcium chlorides, 

 MgCl 2 and CaCl 2 , are 0-194 and 0-164, and of sodium and potassium 

 chlorides, NaCl and KC1, 0-214 and 0-172, and therefore their molecular 

 heats (or the products QM, where M is the weight of the molecule) are 

 18-4 and 18-2, 12-5 and 12-8, and hence the atomic heats (or the 

 quotient of QM by the number of atoms) are all nearly 6, as with the 

 elements. Whilst if, instead of the actual atomic weights Mg = 24 

 and Ca = 40, their equivalents 12 and 20 be taken, then the atomic 

 heats of the chlorides of magnesium and calcium would be about 4-6, 

 whilst those of potassium and sodium chlorides are about 6-3. 5 We 



It must be remarked that in the case of oxygen (and also hydrogen and carbon) 

 compounds the quotient of MQ/w, where n is the number of atoms in the molecule, is 

 always less than 6 for solids; for example, for MgO = 5'0, CuO = 5'l, MnO 2 = 4-6, ice 

 (Q = 0-504) = 3, Si0 2 = 8'5, &c. At present it is impossible to say whether this depends 

 on the smaller specific heat of the atom of oxygen in its solid compounds (Kopp, Note 4) 

 or on some other cause ; but, nevertheless, taking into account this decrease depending 

 on the presence of oxygen, a reflection of the atomicity of the elements may to a certain 



