1835.] Heat of Bodies to their Atomic Weights, 37 



According to the law of Dulong and Petit, the specific 

 heat of simple bodies, taking for unity that of an equal 

 weight of water, multiplied by their atomic weights, gives 

 us the constant number -375, (or -376*) In other words, 

 the specific heat of an atom of these bodies is '375, adopting 

 as unity the specific heat of a body of water, equal in weight 

 to that of an atom of oxygen. From which it follows that 

 if the same law applies to oxygen, and if the relation 

 adopted between the atoms of different bodies and that of 

 oxygen, is really that which exists between the atoms, to 

 which the law refers, and which maybe called their thermic 

 atoms, the specific heat of oxygen in the solid state, ought to 

 be 0*375, taking as unity that of an equal weight of water. 

 This, however, cannot be verified by experiment, because we 

 are unacquainted with any method of operating upon oxygen 

 in the solid state. It is obvious, therefore, that to fix the 

 atoms of bodies relative to oxygen, is somewhat arbitrary ; 

 for the rule of the equality of the specific heat of atoms, 

 would be verified by doubling or trebling all the atoms in 

 relation to that of oxygen, or in taking a half or third, pro- 

 vided that we changed at the same time the constant number. 



Let us turn our attention to various bodies with this object 

 in view. 1. The specific heat of carbon appears to indicate 

 that we may reduce the atoms of sulphur, and the metals, to 

 one-half of the numbers attributed to them at present. The 

 atom of carbon is really 0-764 (or rather -75, as will be pre- 

 sently seen) of the atom of oxygen. The same relation ought 

 then to subsist between the atoms of carbon and oxygen, 

 both in the solid state, in order that the law of Dulong and 

 Petit may be applicable. The specific heat of carbon, 

 according to the determination of Crawford and Avogrado, 

 is -25, or one fourth of that of water. Now, '75, the true 

 atom of carbon (and not -764, the number adopted on the 

 Continent) + '25 = -1875, or the half of -376, and exactly 

 the half of -375, the co-efficient adopted by Avogrado. 

 From this fact Avogrado argues that the co-efficient of the 

 law of Dulong and Petit ought to be reduced to this half 

 number, -1875, and for the same reason that the atoms of 



* Thomson on Heat and Electricity, 97.. 



