532 Mr. T. S. Hunt on the Theory of Chemical Changes , 



species from the density of its vapour, the inquiry arises whether 

 a definite and constant relation may not be discovered between 

 its vapour-density and the specific gravity of a species in the 

 soUd state. Such a relation being established, and the value of 

 the condensation in passing £i-om a gaseous to a solid state being 

 known, the equivalents of solids, like those of vapours^ mieht be 

 determined from their specific gravities. .' ^,<4v.^u«^'> A\ntt?. ^^^ 

 "A connexion between equivalent weight and denfiky is evident 

 in some allied and isomorphous species. H. Kopp, in dividing 

 the assumed equivalent weights of sucb bodies by their specific 

 gravities, obtained quantities which were found to be equal for 

 some of these related species. These numbers evidently repre-* 

 sent the volumes of equivalents, and in accordance with the 

 atomic hypothesis, are said to denote the atomic volumes. The 

 inquiry of Kopp has been pursued by many investigators, amon^ 

 whom are Schrceder, Filhol, Playfair and Joule, and more re- 

 cently, Dana. Their results show that the volumes thus calculated 

 for related species of similar crystallization are generally identicaly 

 or sustain to each other some simple ratio j while Mr. Dana, who 

 has compared isomorphous species of unhke chemical constitu- 

 tion, finds that the calculated volumes are often to each other as 

 the number of equivalents of elements in theforaiulas represent- 

 ing the species; thus leading to the conclusion that the real 

 equivalent weight is either a mean of that of all the elements, or 

 some multiple of it. The reason of this appears in the fact that 

 the formulas of those species in which this relation is apparent, 

 generally difier in the proportions of Al* 0^, SiO^, MgO, CaOy. 

 &c., and the quantities obtained in dividing the equivalents 

 weights of these by the number of elements are nearly equal. » 

 K we divide by the number of elements the equivalents calcu* 

 lated from the formulas of those species, it will be seen that the 

 mean equivalents vary with the specific gravity. 



These investigations have been principally confined to native 

 and artificial mineral species, and the equivalents have been cal- 

 culated from the formulas of Berzelius and Rammelsberg, which 

 express the simplest ratios deducible from analysis. While in 

 conformity with the dualistic notions, a mineral like calcite or 

 magnesite was regarded as a compound of one equivalent of car- 

 bonic acid and one of lime or magnesia, dolomite was said to be 

 composed of one equivalent of each of these carbonates, or of 

 two to three, as the case might be, while its density was the 

 mean of those of its constituents ; thus implying that this union, 

 unlike that observed in gases, is juxtaposition, and not interpenc-' 

 tration. This system of formulas has introduced such difficulties 

 into the study of the relations before us, that we find Mr. Dana 

 led to the conclusion that '' the elemental molecules are not com- 



