SECT. in. IN WEIGHT AND VOLUME. 103 



It follows from the atomic theory that the number of 

 atoms in equal weights of any two solid substances, is 

 in the inverse ratio to the weights of these atoms. 

 Now since the bodies that have the greatest specific 

 gravities are the heaviest, if the specific gravities and 

 atomic weights of equal bulks of two simple substances 

 be known, the relative number of atoms they contain 

 may be found. For the density divided by the atomic 

 weight of the one, is to the density divided by the 

 atomic weight of the other, as the number of atoms in 

 the first to the number of atoms in the second. By 

 the preceding law it is found that in equal bulks of the 

 three metals, sodium, platinum, and potassium, platinum 

 contains five times as many atoms as sodium, and ten 

 times as many as potassium. When substances which 

 have strong analogous qualities are compared in this 

 manner, the results are either equality, or a simple 

 ratio. 



It has already been mentioned that the protoxides 

 of iron, copper, zinc, nickel and manganese, have the 

 same form, and contain the same quantity of oxygen, 

 but differ in the respective metals that are combined 

 with it ; and by the preceding law it appears that equal 

 bulks of these isomorphous bodies contain also the same 

 number of atoms. 



Mr. Hermann Kopp has proved that the atomic weight 

 of a substance divided by the specific gravity, that is 

 to say, its atomic volume, is the same for all isomorphic 

 bodies simple and compound, and as a general law that 

 the atoms of isomorphous substances are not only the 

 same in form, but equal in dimensions. It follows, 

 therefore, that any one of the preceding metals might 

 be substituted for any other in the respective prot- 

 oxides, and on that account, according to the modern 

 theory, they are the chemical equivalents of each other, 

 for that expression is used now in a different sense from 



