5^8 BUNSEN ON THE FORMATION OF 



tions of volcanoes. The objections which are supposed to be 

 fatal to the old volcanic theory of Davy entirely lose their value 

 after these results. For if, in the spirit of this theory, it is 

 assumed that the lavas, and the pha3nomena of ignition accom- 

 panying them, result from an oxidation of alkaline and earthy 

 metals determined by a decomposition of water, it admits of 

 being proved, quite in contradiction of the views which have 

 hitherto been entertained, that the quantity of the hydrogen 

 evolved from volcanoes bears a perfect relation to the magnitude 

 of the streams of lava formed. A. single one of the vapour 

 springs of Krisuvik yields, according to the measurement quoted 

 above, about 12 cubic metres of hydrogen in twenty-four hours. 

 Assuming, then, that the remaining innumerable springs, toge- 

 ther with the large fumaroles occurring there, yield together ^ 

 quantity only one hundred times as great — which may safely bq 

 regarded as far less than the quantity of this gas which is ac- 

 tually evolved — we may by means of this assumption and simple 

 calculation show, that the formation of lava which would be 

 equivalent to such an evolution of gas within the period which 

 elapses between two great eruptions, is sufficient to produce im- 

 mense streams of lava. Nor is it any longer possible to attach 

 any importance to the second of the principal objections which 

 have been made to Davy's hypothesis, namely, that it is unusual 

 to observe any sensible appearance of flames during great vol- 

 canic eruptions. For if, from the known composition of the 

 first-mentioned fumarole gas, we estimate the temperature of its 

 flame, we find it to be 305°*6 ; consequently a temperature 

 which is far below the point of ignition of hydrogen. 



These gases are therefore combustible only at a red heat, and 

 even under the most favourable circumstances can only produce 

 by such a combustion an increase of temperature amounting to 

 305°*6, which in a red heat must necessarily escape altogether 

 observation by the eye. 



Since, as I have already pointed out, the palagonitic meta- 

 morphism is likewise accompanied by a disengagement of hydro- 

 gen, it would appear almost impossible that there should be any 

 doubt as to the source of this gas. However, the constitution 

 of the mixture of gas examined affords in itself a direct proof that 

 neither the formation of palagonite nor a decomposition of water 



