224 Analyses of Books. [Sept. 



. " But under the sea, where the pressure of an enormous 

 column of water assists in forcing that fluid through the minutest 

 crevices of the rock, the action must go on more rapidly, and 

 the effects consequently be of a more striking nature. 



" These effects, however, will take place in the middle of the 

 sea less generally than on the coast, because the pressure of 

 the ocean itself opposes an impediment ; and it will in general 

 not be constant, but intermittent, because the heat generated by 

 the process itself, will have a tendency to close the aperture by 

 which the water entered, first, by injecting the fluid lava into 

 the fissure ; and, secondly, by causing a general expansion of 

 the rock ; nor will the water again find admission, until, owing 

 to the cessation of the process, the rock becomes cool, and 

 consequently again contracts to its original dimensions." 



*' Now the first effect of the action of water upon the alkaline 

 and earthy metalloids, will be the production of a large volume 

 of hydrogen gas, which, if air be present, will combine with 

 oxygen and return to the state of water ; if it be absent, will 

 probably combine with the sulphur, both being at the high 

 temperature favourable to their union. In the former case, 

 nitrogen gas will be given off; in the latter, sulphuretted 

 hydrogen. 



"But in case of the presence of oxygen, the sulphur will also 

 become inflamed, and give rise to the production of sulphurous 

 acid, which will predominate among the gaseous exhalations 

 emitted from the mouth of the volcano, provided a sufficient 

 quantity of air be present to combine with the hydrogen, and 

 re-convert it into water. So soon, however, as the oxygen is 

 consumed, the hydrogen, no longer entering into combustion, 

 unites with the heated sulphur, and escapes m the form of sul- 

 phuretted hydrogen, which, towards the latter period of the 

 eruption, will predominate over the sulphurous acid, because it 

 continues to be formed, long after the want of oxygen has put a 

 stop to the production of sulphurous acid. Now it is well 

 known, that these two gases mutually decompose each other, 

 and, therefore, cannot exist at the same time, so that the appear- 

 ance of sulphuretted hydrogen from the mouth of the volcano, 

 may indicate, if not the entire absence of sulphurous acid, at the 

 place at which the process takes place, at least that its forma- 

 tion is stopped by the consumption of oxygen, or is going on 

 with less energy than heretofore. 



" The very circumstance of the reproduction of water by the 

 mutual decomposition of these two gases, might be the means 

 of keeping up the action, in a languid manner, for an indefinite 

 period. The slowness with which lava cools, would cause it to 

 give out, for a considerable time, sufficient heat to the adjoining 

 strata, to place the sulphur at the temperature necessary to 

 cause its combination with oxygen ; hence a certain portion of 



