258 .Rev. J. B. Emmet t on the [April, 



force greater than the other assisting forces. For example, in 

 solution, potash and soda separate all the metallic oxides from 

 most acids, because, by reason of cohesion, the oxides are inso- 

 luble. Barytes separates potash and soda from most of their 

 salts, and nearly all the resulting compounds of barytes are inso- 

 luble. Lime separates them from those acids with which it 

 forms insoluble compounds, but in no other cases. Although 

 the force does not become actual cohesion, until the compound 

 is formed, we here see the operation of the force which ulti- 

 mately produces cohesion, while the particles are yet separated. 

 These remarks need not be further extended, since they are 

 obvious to every reader. 



Electricity appears to be most intimately connected with this 

 subject. In all cases of electrical excitation, the opposite states 

 are always exhibited in such proportion as will mutually neu- 

 tralize each other, whether excited in the ordinary manner, or 

 by chemical agency, as in the galvanic series, if compound 

 bodies, as neutral salts, be exposed to the operation of the gal- 

 vanic battery, the principles are separated from each other ; oxy- 

 gen, chlorine, and acids appear at the positive pole, while hydro- 

 gen, azote, and inflammable matter, together with earths, alka- 

 lies, and metallic oxides, tend to the negative ; and those bodies 

 which unite with the greatest force differ most in their natural 

 electric energy. Electricity is excited by the contact of dissi- 

 milar bodies, when the same relation is observed, with this pecu- 

 liar difference, that bodies of the same class have different 

 degrees of electric energy, whereby, after contact, the two elec- 

 tricities are exhibited. Whether electricity be the cause of 

 chemical combination or a counteracting force, cannot yet be 

 determined ; and for the purposes of research, it is not material 

 that this should be decided. However, until the several electric 

 energies of bodies be determined, as well as the relation of the 

 electric energy to caloric, to the atomic weight, specific gravity, 

 8tc. nothing can be determined with certainty. I therefore 

 withhold further researches into the nature, &.C of chemical 

 combination for the present, except that all tables of capacities 

 of bodies for heat, expansion, &.c. should be computed for 

 weights proportional to the atomic weights, for then they repre- 

 sent the capacities, ike. of single atoms ; this is most conspicu- 

 ous in cases of combustion. Since heat is evolved during that 

 process, there must be a diminution of capacity ; if, therefore, 

 we add the atomic capacities of the bodies, and from the sum 

 subtract the atomic capacity of the product (that is, the capacity 

 of a weight of the product, equal to the sum of the weights of 

 the ingredients consumed), the remainder will be the proportion 

 of the diminution of capacity, or of the heat evolved ; for 

 example, the atomic capacity of hydrogen gas is 2'82 ; that of 

 oxygen is 4-75 ; the sum is 7*57 \ the capacity of an atom of 

 aqueous vapour is 1-75; therefore, 5'82 is the heat evolved. 





