430 ON THE THEORY OF CHEMICAL CHANGES. [XVI. 



apparent exceptions to the general law of condensation and 

 equivalency of volumes. When four volumes of chlorine unite 

 with four of olefiant gas, or of naphthaline, the product is con- 

 densed into four volumes ; but if the chlorine unite with the 

 same volume of hydrogen gas, there is no condensation, and 

 eight volumes or two equivalents of hydrochloric gas are pro- 

 duced. This, however, is explained when we find that four 

 volumes of the chloro-hydrocarbon, MH,C1 2 , may break up 

 into four of a new species MCI, and four of HC1 ; a change 

 which with the chloride of olefiant gas is effected by the aid of 

 hydrate of potash, and with the chloride of naphthaline takes 

 place spontaneously at an elevated temperature. In the pro- 

 duction of hydrochloric gas from chlorine and hydrogen, union 

 takes place followed by immediate expansion without specific 

 difference, or metamorphosis, while in the production of this 

 acid 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 theo- 

 retical volumes, so that four volumes of hydrogen gas represent 

 not H, but H 2 . In the same way, if we conceive the quantity 

 of oxygen produced from four volumes of water- vapor to repre- 

 sent two equivalents, it should equal eight volumes instead of 

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

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

 As there are no bodies wliich are known to yield for four vol- 

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

 taken to represent its equivalent, and the condensation of the 

 theoretical volume is, like that of hydrogen and chlorine, one 

 half. Water with an equivalent of four volumes is then H 2 O, 

 and its weight 2 + 16 = 18; the same formula is deduced l>y 

 those chemists who take two volumes for the equivalent, and, 

 dividing the weight of hydrogen, write water H 2 0, with ;ui 

 equivalent weight of 9. The condensation of these elements 

 is that mode of metamorphosis which constitutes polymerism, 



