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



the specific gravity increasing. Monoclinic and triclinic crystals 

 may be calculated as if derivative^ of the trimetric system, with 

 which they will be found to correspond in volume. 



It is now necessary to determine what equivalent corresponds 

 to a given specific gravity in any crystalline solid, or in other 

 words, what is the value of the condensation which takes place 

 in the change from the gaseous to the solid state ; and here a 

 degree of uncertainty is met with, because the equivalent of a 

 crystallized species may often be a multiple of that deduced from 

 those chemical changes which only commence with the destruc- 

 tion of its crystalline individuality. The simplest formula de- 

 ducible for alum is KO SO^ AFO^SSO^, 24H0, or S^Kal* 

 O^^, 12H*0^, and hydrogen being unity, its equivalent is at 

 least 4;74'6, which with a specific gravity of 1*75, gives a volume 

 of about 270. Again, grape-sugar is not less than C^ H^'* 0^'*, 

 if we regard its combination with common salt as corresponding 

 to one equivalent of each, and the ferrocyanides in the same way 

 are represented by C^^, &c. ; there are reasons for believing that 

 the equivalents of these species in the crystalline state coiTespond 

 to some multiple of the above formulas, a question to be decided 

 by an examination of the crystallization and specific gravity of 

 species whose equivalents are admitted to be higher. 



Favre and Silbermann, from their researches upon the heat 

 evolved in fusion and solution, have been led to conclude, first, 

 that crystallized salts are polymeric of these same salts in solu- 

 tion, i. e. are represented by formulas which are multiples of 

 those deduced from analysis; secondly, that double salts and 

 acid salts do not exist in solution, being produced only during 

 crystallization ; and thirdly, that water in crystallizing changes 

 from HO to nHO, n being some whole number*. These con- 

 clusions are seen to be in accordance with these deduced from a 

 consideration of the relations of density and equivalent volume ; 

 a polymerism is evident in such salts as sulphate of potash and 

 cyanide of potassium, when their specific gravities are compared 

 with those of alum and the ferrocyanide. 



In the liquid state, the relation between specific gravity and 

 equivalent is not so apparent in solid species. The condensation 

 often varies greatly, even in allied and homologous species, but 

 still exhibits a relation of volumes. The alcohols C* H'* 0^ C^ 

 H«02, C10H12O2, and Ci^H^sQa^ jj^ve very nearly the same 

 specific gravity, so that the condensation is inversely as their 

 vapour-equivalents. The densities of wine-alcohol, acetic acid 

 and aldehyd in the liquid state, vary as their equivalents, so that 



• Comptes Rendus, xxii. 823-1140, andxxiii. 199-411 ; cited in Liebig 

 and Kopp's Annual Report for 1847-48, vol. i. p. 40, 



