Reply of Dr. Dauheny to Prof, Bischof 81 



than the frequent associations of it with volcanos is, if we do not 

 have recourse to this hypothesis. 



Wi Objection, — The metals of the earths are not sufficiently 

 oxidizable to kindle on the access of water, and to produce the 

 intense heat which would be necessary for producing and Hque- 

 fying lavas. 



Ajiswer. — Sihcon, though when pure it is incapable of decom- 

 posing water, and is incombustible in oxygen, yet kindles readily 

 when united either with a little hydrogen or with alkaline car- 

 bonates. Aluminium, even by itself, burns brilliantly when 

 heated above redness, and dissolves with the evolution of hydro- 

 gen in very dilute sokitions of potassa. 



Calcium and magnesium appear to be still more inflammable, 

 and the bases of the alkalies, present along, and perhaps in com- 

 bination with them, might, whenever water obtained access, 

 generate heat sufficient to cause the other bases to enter into 

 combination with oxygen. Besides, we know that aluminium 

 and magnesium enter readily, with an evolution of heat and 

 hght, into combination with chlorine, a body which (as we shall 

 see) there is good reason for supposing present in volcanos. 



7th Objection. — Tfie slight specific gravity of the metals of 

 the alkalies proves fatal to Davy's hypothesis, for, if the mean 

 density of the earth surpass that of all kinds of rocks, these 

 metals cannot exist, at least not in great quantities, in the inte- 

 rior of the earth- 

 In reply to this I cannot do better than extract the remarks 

 which I made in reply to the self same objection in my article 

 on volcanos, published in the Encyclopaedia Metropolitana in the 

 year 1833. 



'* An objection against our hypothesis has also been somellmRS dednced from 

 the mean density of the Earth, which is calculated at five times that of water j 

 and hence it has been concluded, that bodies so light as potassium and sodium are, 

 cannot make a part of its nucleus. 



But we are not obliged to imagine a larger proportion of these alkaline bases to 

 be present, than would be implied by the composition of the lava emitted, and 

 probably we shall find not more than four or fire per cent, of potassa or soda to 

 exist, in the average of volcanic productions. 



On the other hand, the specific gravity of the basis of silica, and probably, also, 

 of that of the other earths wliich predominate in lava, is sufficiently con=;iderable 

 to warrant the conclusion, that a mass of matter, containing these principles in the 

 proportions indicated, and united with as much metallic iron as we know to exist 

 in the state of an oxide in the generality of lavas, would form an aggregate pos- 



Vol. XXXVII, No. 1.— July, 18A bis. H 



