1835.] Heat of Bodies to their Atomic Weights. 35 



The affinitary number is obtained by dividing the atomic 

 weight of a body by that of potassium, which is considered 

 unity ; thus, the affinitary number of gold will be ^f.5=2'5, 

 or, as Avogrado makes it, 2a:a6— 5-073. Then m = 5*073, 



£/=22-18and6Z=^ora=^ygivesa = ^f^^^ = '6115, 



the affinity of gold for heat. 



M. Avogrado, by his experiments on the specific heat of 

 bodies, has confirmed the accuracy of the law deduced by 

 Dulong and Petit, from their researches, that the specific 

 heat of the atom of a compound gas is expressed hy the square 

 root of the whole, or fractional number of the atoms of the 

 simple gases, hy whose combination the compound atom is formed. 

 He has, however, been more particular in his expression of 

 the law, which, according to him, is of the following import : 

 the specific heat of an atom of a compound body is equal to the 

 square root of the whole, or fractional number, expressing the 

 atoms or portions of atoms which, by their combination, form 

 the atom of the compound body, whether in the solid or liquid 

 state, adopting as unity the specific heat of some simple body 

 in the same state. This rule, however, is not easily applied 

 to solids and liquids, because the atoms and volumes of 

 gases are equivalent ; whereas, in the former classes, it is 

 a question requiring much investigation to resolve, what is 

 the composition of the compound atom in the solid or liquid 

 state. For the composition, according to theoretical con- 

 siderations, is often different from what it is in the gaseous 

 or vaporific state. Impressed with a desire of clearing up 

 this difficulty, Avogrado was led into the discussion of the 

 subject of the atomic weight of bodies, and has considered 

 it proper to reduce the numbers attached to them by the 

 Continental chemists to one-half. These new numbers being 

 deduced from the consideration of the specific heat, he has 

 termed them thermic atoms. The table of the specific heat 

 of bodies, which was the result of his researches, has been 

 already presented to the reader (Records of General Science, 

 vol. i. 108.) The numbers were ascertained by means of an 

 instrument of simple construction. The vessel in which 

 the substance to be experimented on was placed, consisted 

 of a cylinder of thin brass, with a flat, upper edge. To this 

 is applied a brass plate, pierced with three holes in its 

 circumference, to enable three screws to pass which rise 



D 2 



