TIIF. VALKNCV AND sl'KCIFIC HEAT OF THE METALS 577 



metals. Thus, for instance, the specific heats of lithium, sodium, and 

 potassium convince one of the fact that their atomic weights are 

 indeed those which we took, because by multiplying the specific heats 

 found by experiment by the corresponding atomic weights we obtain 

 the following figures : Li, 6 -59, Na, 6 '75 and K, 6 '47. Of the 

 <dkaline earth metals the specific heats have been determined : of mag- 

 nesium = 0-245 (Regiiault and Kopp), of calcium=0'170 (Bunsen), and 

 of barium=0'05 (Mendeleeff). If the same composition be ascribed to 

 the compounds of magnesium as to the corresponding compounds of 

 potassium, then the equivalent of magnesium 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 

 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.j for example CaCl 2 , CaSO 4 , CaO (Ca=40) we obtain an atomic 

 heat=40x 0-17=6-8, and for barium it is equal to 137x0-05=6-8; 

 that is, they must be counted as bivalent, or that their atom replaces 

 H.>, Na 2 , or K 2 . This conclusion may be confirmed by a method of 

 analogy, as we shall afterwards see. A strict application of the prin- 

 ciple of specific heats to the determination of the magnitudes of the 

 atomic weights of those metals, the magnitude of whose atomic weights 



to 6 as with other elements. Thus with the diamond and charcoal, it is evident that the 

 specific heat tends towards 0'47, which multiplied by 12 gives 5 '6, the same as for mag- 

 nesium and aluminium. I may here turn the reader's attention to the fact that for 

 solid elements having a small atomic weight, the specific heat varies considerably if we 

 take the average figures for temperatures to 100 : 



Li = 7 Be = 9 B =11 C = 12 



Q = 0-94 0*42 0'24 0'20 



AQ = 6'6 8-8 2-6 2'4 



It is therefore clear that the specific heat of beryllium deteTmined at a low temperature 

 cannot serve for establishing its atomicity. On the other hand, the low atomic heat of 

 charcoal, graphite, and the diamond, boron, &c., may perhaps depend on the complexity 

 of the molecules of these elements. The necessity for acknowledging a great complexity 

 of the molecules of carbon was explained in Chapter VIII. In the case of sulphur the 

 molecule contains at least S 6 and its atomic heat = 82 x 0'168 = 5'22, which is distinctly 

 below the normal. If a great number of atoms of carbon are gathered together in the 

 molecule of charcoal, this would to a certain extent account for its comparatively small 

 atomic heat. With respect to the specific heat of compounds it will not be out of place 

 to here mention the conclusion arrived at by Kopp, that the molecular heat (that is, the 

 product of MQ) may be looked on as the sum of the atomic heats of its component 

 elements ; but as this rule is not a general one, and can only be applied to an approxi- 

 mate judgment of the specific heats of substances, I do not think it necessary to go into 

 the details of the conclusions described in Liebig's ' Annalen Supplement-Band,' 1864 ; 

 which includes a number of determinations made by Kopp. 



VOL. I. P P 



