^•%, 



I -^ 



been 



pa- 



e 



^ 



Atl^, 



C 



use 

 savs 



c; 



siTe 



ered, 

 a?es. 



uliai" 



lities 



me 

 jreat 



'e at 

 mo); 



rra- 



kor 



the 

 the 



.^ter 

 ■be 



r 



(Til' 



the 



* 



I 



I 



Ch. XXXIIL] 



CHEMICAL ACTION. 



233 



geologist : for silica, alumina, lime, soda, and oxide of iron 



substances of wliicli lavas are principally composed 

 would all result from the contact of tlie inflammable metals 

 "'alluded to with water. But Avhen Davy failed to detect, 

 dinging an eruption of Vesuvius, any hydrogen among the 

 gaseous products ev^olved from the crater, he was disposed to 

 renounce or to attach but little importance to his theory. 



We have seen (p. 225) that it is now ascertained that hydro- 

 gen is disengaged during eruptions in large quantities ; but, 

 according to M. Fouque, there is always much more proto- 

 carbonate of hydrogen than free hydrogen, w^hereas the 



reverse ought to be the case, if these combustible gases 

 resulted from the contact of alkaline metals with w^ater."^ 

 The same chemist remarks, that to explain the disengagement 

 of heat during the last eruption of Etna, we should require 

 a mass of sodium of at least 7,000,000 cubic metres, and 

 therefore the quantity of alkalinq metals beneath all the 

 active volcanos, which has given rise in each to a long series 

 of eruptions, would be incredibly great. 



M. Fouque is satisfied with the hypothesis of a subterranean 

 sheet of fluid lava, to w^hich water occasionally may gain 

 access, central heat being invoked as the power by which 

 the lower parts of the earth's crust are retained in a melted 

 state, and no explanation being attempted by him of the 



om 



envelope to another. 



In former editions, I have suggested that if the accumu- 

 lation of heat be granted as successively developed in 

 different parts of the earth's shell, we may readily conceive 

 that the waters of lakes and seas misrht P^ain access to the 





fluid lava during earthquakes, large bodies of water bein^ 

 occasionally engulfed, and then, when the sides of the 

 fissures closed again with violence (see page 125), the steam 

 generated bj contact of the water with the heated subterra- 

 nean fluid, would not escape by the same rents, but might 

 rush out with lava from some distinct and perhaps habitual 



* Fouqu6, Rapport sur les Phenomenos Chimiques de rEruption de I'Etna 

 enl865, p. 80. 



M 



