SECT. m. AND ELECTRICITY. 101 



a given temperature, is inversely as the weight of its 

 atoms, so that the specific heat or repulsive force of 

 simple substances multiplied by their atomic weights is 

 a constant quantity. Such is the condition requisite 

 for the equilibrium or equality of force ; or the law may 

 be thus expressed : A given quantity of heat will raise 

 to the same number of degrees a portion of every simple 

 substance represented by its atomic weight. For in- 

 stance, the atomic weight of sulphur is 16, that of zinc 

 32 ; hence it requires twice as much heat to raise a 

 pound of sulphur ten degrees as it does a pound of zinc. 

 It has also been proved that the atoms of compound 

 bodies of analogous composition are endowed with the 

 same capacity for heat, so that there is a perfect cor- 

 respondence between the weight of atoms and their 

 specific heat. The numbers representing the atomic 

 weights derived from the specific heat of bodies are 

 connected with their equivalent atomic weights by the 

 simple ratios of equality, multiples or sub-multiples. 



Mr. J. Croll has made experiments showing that the 

 specific heat of compound gases and liquids is generally 

 less, and those of solids more, than that of their com- 

 ponent elements, which is contrary to the hitherto 

 received opinion. Moreover it appears that the changes 

 in the specific heat of bodies which occur during com- 

 bination are not only due to chemical action, but also 

 to molecular changes ; the real specific heat of a simple 

 atom probably remaining the same under all conditions. 



Mr. Faraday has proved that the specific electricity of 

 different substances is also in proportion to their atomic 

 weights, that is to say, a given quantity of electricity 

 will separate combined substances into parts represented 

 by their atomic weights. For example, 32 parts of 

 zinc will generate voltaic electricity enough to separate 

 nine parts of water into eight parts of oxygen and one 

 part of hydrogen gas. The weights thus derived from 



