138 Mr J. Girardin's Remarks on Sir H. Davy's 



metals, would be the production of an enormous quantity of 

 hydrogen, and, in consequence of the combustion of that gas on 

 coming into contact with the air, the disengagement by the vol- 

 canic crater of a prodigious mass of aqueous vapour. Abun- 

 dance of such vapour is, in fact, observed during all eruptions ; 

 but it is difficult to conceive that all the hydrogen rendered free 

 is burnt ; for, however large the subterranean cavities may be 

 which Sir H. Davy admits under the ignivomous mountains, it is 

 more than probable that there does not exist in them a quantity 

 of air sufficient to produce the combustion of the enormous vo- 

 lume of hydrogen which must be disengaged. Besides, it is 

 impossible, supposing the two gases to be in suitable proportions, 

 that a part of the hydrogen should not escape ignition, being 

 carried away by the aqueous vapours, the acid gases and the 

 saline sublimations, which are formed at the same moment. From 

 these circumstances, there ought to be found a pretty large 

 quantity of hydrogen among the aeriform products which issue 

 from the craters. Now, observation proves that the disengage- 

 ment of this gas is very rare in eruptions. It might then be 

 supposed that this gas, at the moment when it is about to issue 

 from the volcanic caverns, combines with some other combustible 

 body. Of all the hydrogenous compounds with which we are 

 acquainted, the only ones observed in volcanic places are ammo- 

 niacal salts, sometimes sulphuretted hydrogen, and always hydro- 

 chloric acid. The ammoniacal salts, whose base would be de- 

 rived from the combination of hydrogen with the azote of the 

 decomposed air, and the sulphuretted hydrogen, are in too small 

 quantity for us to calculate upon a great absorption of hydrogen 

 by these compounds. It would, therefore, be with the chlorine 

 that nearly the whole of the hydrogen would unite; but then it 

 would be necessary to admit that the metals are partly in the 

 state of chlorurets in the interior of the earth, as has also been 

 advanced by some chemists. In the first place, according to 

 this supposition, the quantity of hydrochloric acid produced 

 ought to be considerable. This is not the case, however. All 

 the naturalists who have observed the phenomena of volcanoes 

 on the spot, have been sensible, that, at the moment of the erup- 

 tions, this acid was produced, but none of them have stated it 

 to have been in extraordinary proportions. Moreover, the me- 



