186 On the Specific Weight of Chemical Compounds. 



Dr. Kopp then goes on to disprove the assumption of 

 Schroder, viz that the atomic volume with which an element 

 is contained in a compound, bears a simple relation (|, ^ — i; 

 •y, § — ^; f, f, § — f) to its primitive atomic volume. 



Sesquioxide of ii'on, sesquioxide of cobalt, ilmenite, and 

 oxide of chromium are all nearly isomorphous. Their atomic 

 volumes are nearly equal. 



Calculated from the different 

 > densities as given by differ- 

 ent observers. 



The atomic volumes obtained from the formulae given above, 

 are — 



Fe^O^ = 184^ 



Co^O^ =184 I which agree tolerably well with the 



Ilmenite = 197 f preceding values. 



Cv^O" = 186 J 



According to the atomic theory, in regard to the composi- 

 tion in equivalents, the four above-mentioned oxides are per- 

 fectly similar in their composition ; but according to the theory 

 of atomic volumes, as regards the manner in which the atomic 

 volumes of the compounds are composed, there is a total dis- 

 similarity. 



In the oxides of iron and cobalt, and in ilmenite, the atomic 

 volume of oxygen is 32 ; in that of chromium it is 16. Oxide 

 of iron and oxide of chromium are isomorplious ; they have 

 however not the same constitution in atomic volumes. The 

 sums of the atomic volumes of the elements in both compounds 

 are equal; the atomic volume of oxide of iron is equal to that 

 of oxide of chromium. In the oxide of iron each atom of iron 

 occupies a space = 44 ; each atom of oxygen a space = 32 ; 

 in oxide of chromium an atom of metal occupies a space = 69y 

 and an atom of oxygen a space =16. How can this be ex- 

 plained if these compounds are formed by simple juxtaposition 

 of their elements ? The same form can never be obtained by 

 laying together two balls, each of which contains 44 cubic 

 unities (inches, feet, &c.), and three balls of 32 cubic unities 

 contents, as by putting together two balls, containing each 

 69 cubic unities, with three balls of 16 cubic unities, although 

 2-44 +• 3-32 is nearly equal to 2-69 + 3'16. Other similar 

 cases might be adduced, and they are altogether contrary to 

 the idea of juxtaposition. Dr. Kopp is almost inclined to 

 assume a penetrability of matter. 



It appears tlial there are cases in which an element, com- 



