fl80 Mr. T. S. Hunt on the Theory of Chemical Changes, 



phosis, while in its production with the hydrocarbons we observe 

 the intermediate stage. 



If an equivalent of four volumes of hydrochloric gas were to 

 undergo a change like the chloride of naphthaline, and yield four 

 volumes of chlorine and four of hydrogen, these species would 

 appear with one -half their observed densities ; hence we con- 

 clude that they are actually condensed to one-half their theore- 

 tical volumes, so that four volumes of hydrogen gas represent 

 not H, but H*. In the same way, if we conceive the quantity 

 of oxygen produced from four volumes of water-vapour to re- 

 present two equivalents, it should equal eight volumes instead of 

 two, so that it is condensed to one-fourth, precisely as the vapour 

 of sulphur is condensed to one-twelfth of its theoretical volume. 

 As there are no bodies which are known to yield for four volumes 

 a less quantity than two volumes of oxygen, this may be taken 

 to represent its equivalent, and the condensation of the theore- 

 tical volume is like that of hydrogen and chlorine, one-half. 

 Water with an equivalent of four volumes is then H^ 0, and its 

 weight 2 + 16 = 18; the same formula is deduced by those 

 chemists who take two volumes for the equivalent, and dividing 

 the weight of hydrogen, write water H^ O, with an equivalent 

 weight of 9. The condensation of these elements is that mode 

 of metamorphosis which constitutes polyraerism, and evidently 

 offers no exception to the law of equivalent volumes. 



The law of Laurent, " that the number of atoms of hydrogen, 

 or of hydrogen, chlorine, nitrogen, metals, &c., in any formula, 

 corresponding to four volumes of vapour, is always a sum divi- 

 sible by two," clearly follows from the principles already laid 

 down, and from the fact that nitrogen and the metals are sub- 

 ject to the same conditions as hydrogen and chlorine ; the atoms 

 have the value which has been assigned to H and to CI in the 

 formulas given above. The same rule of divisibility, as Laurent 

 has already shown, necessarily holds in regard to the number of 

 atoms of carbon, as well as to the oxygen and sulphur, if we 

 take for their equivalent weights the numbers 6, 8 and 16 

 respectively*. 



It is to be remarked that while the coefficients of H, CI or N, 

 ill formulas where these are associated, may be odd numbers, 

 those of O, S, and C are always even ; this seems a conclusive 

 reason for doubling the equivalents of the latter, or dividing 

 those of hydrogen, chlorine, the metals, &c., according as four 

 or two volumes are taken for the equivalent. 



I have elsewhej-e pointed out that carbon and oxygen sustain 



* See Laurent's Recherches sur les combinaisons azot^es, Ann. de Chimie 

 €t die Physique, Nov. 1846, and the American Journal of Science for Sept. 

 1848, p. 174, 



