opinions respecting Volcanic Phenomena. 139 



tallic chlorurets of the two first sections, when placed in contact 

 with water at a high temperature, powerfully unite with it, but 

 do not decompose it. The chlorurel of iron alone presents this 

 fact; so that of all the oxides that occur in lavas, iron is the only 

 one that could be originally in the state of a chloruret. In the 

 neighbourhood of burning craters, there are found a considerable 

 number of metaUic chlorurets. These compounds, so far from 

 existing previous to the eruptions, are, on the contrary, formed 

 under our eyes by the reaction of the free hydrochloric acid upon 

 the volcanic rocks. It is true, that Sir H. Davy has discovered 

 that the white fumes which are disengaged from lavas in a state 

 of fusion, are in a great measure composed of chloruret of sodium, 

 and a little chloruret of potassium and iron ; but the quantity 

 of these chlorurets is so small in proportion to the mass of the 

 ejected matters, that they cannot be supposed to exist in very 

 large proportions in the interior of volcanoes. Besides, they 

 ought to form the greater part of the substance of lavas, in which, 

 however, only traces of them are found. From this discussion, 

 there results, that water has not been satisfactorily demonstrated 

 to perform the part in volcanic reactions which Sir H. Davy at- 

 tributes to it. 



Another consequence of the theory of the English chemist is, 

 that the internal parts of the globe would have a very small spe- 

 cific gravity, it being known that the earthy and alkaline metals 

 are generally lighter than water. Now, this great lightness is 

 contrary to all the opinions and all the experiments of natural 

 philosophers, who are generally agreed in attributing to the in- 

 ternal rocks of our planet, a density superior to that of the earth 

 and rocks which compose its surface. According to the calcula- 

 tions of Clairaut, Boscowich, Laplace, and Maskelyne, and the 

 experiments of Cavendish, it may be established that the mean 

 density of the internal nucleus of the earth, compared with that 

 of water, is as 5 to 1.. Consequently, it may be admitted that 

 this nucleus is formed by substances whose specific gravity is 

 inferior to that of water. 



From all these facts and reasonings, to which we could add 

 many others, it appears to us evident that Sir H. Davy's inge- 

 nious theory is insufficient for the explanation of those natural 

 phenomena, whose magnitude and periodical occurrence present 



