1835.] Heat of Bodies to their Atomic Weights. 39 



4. Iodine. — For the specific heat of this substance in the 

 solid state, Avogrado obtained the number -089. 



Now, to procure an approximation to this number tJieore- 

 tically, we must divide the atom 15*75 by '8, and we have 

 1-967. Now, ^1^ = -095. Hence arsenic is analogous to 

 phosphorus. 



We may, perhaps, extend the same analogies to bromine, 

 and chlorine. Avogrado infers that the combining atom of 

 azote is formed of 2 thermic atoms; those of chlorine, 

 iodine, bromine and phosphorus, of 8 thermic atoms, and 

 that of arsenic of 4 true or thermic atoms, each multiple 

 atom requiring 5 atoms of oxygen to form nitric, chloric, 

 iodic, bromic, phosphoric, and arsenic acids. 



Now, with regard to compound bodies, Avogrado consi- 

 ders that the law deduced from the experiments of Dulong 

 for the specific heat of compound gases applies equally to 

 the specific heat of compound bodies in the solid state, viz. 

 that the specific heat of the compound atom of a solid body, 

 taking as unity that of a simple atom, given by the law of 

 Dulong and Petit, is represented by the square root of the 

 whole or fractional number, which expresses the atoms or 

 portions of simple atoms of different kinds, entering into 

 the formation of this compound, a number, which, for brevi- 

 ty's sake, may be termed the constituent number of the com- 

 pound atom. Consequently, to obtain the constant number, 

 •1875, it is necessary to multiply the specific heat of com- 

 pound bodies (taking that of an equal weight of water as 

 unity) first by the weight of the compound atom, taking 

 that of oxygen as unity, as for simple bodies, and to divide 

 by the square root of the constituent number ; and recipro- 

 cally to obtain the specific heat of a solid body, taking as 

 unity that of an equal weight of water, we must multiply 

 the square root of the constituent number by '1875, and 

 divide by the weight of the compound atom. It will now 

 be proper to consider the application of this law to the 

 difi'erent kinds of compound bodies. 



1 . Water. — If we suppose that the atom of water in the 

 solid, liquid and vaporific state is the same, and represent- 

 ing its composition to be 1 atom hydrogen .-}- J atom 

 oxygen, its constituent number will be 1*5 of which the 

 square root is 1*225. Now, let us multiply the square root 



