— i cs 
ay 
Reply of Dr. Daubeny to Prof. Bischof. «81 
than the frequent associations of it with volcanos is, if we do not 
have recourse to this hypothesis. : 
6th 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 lique- 
fying lavas. 
_Answer.—Silicon, 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- 
hates. Aluminium, even by itself, burns brilliantly when 
heated above redness, and dissolves with the evolution of hydro- 
gen in very dilute solutions of potassa. 
Calcium and magnesinm 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 
light, into combination with chlorine, a body which (as we shall 
See) there is good reason for supposing present in volcanos. 
-Tth Objection.—The 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- 
tor-of the earth. 
In reply to this T cannot do better than extract the remarks 
Which [ made in reply to the self same objection in my article 
on vdleanos, published in the Encyclopeedia Metropolitana in the 
Year 1833, 
“An objection against our hypothesis has also been sometimes deduced “— 
the mean density of the Earth, which is calculated at five times that of water 5 
and hence it has been concluded, that bodies so light as potassium and sodium are, 
*amnot make a part of its nucleus. 
exist, in the a 
On the other hand, the specific gravity of the basis of silica, and probably, also, 
of that of the other earths which predominate in lava, is sufficiently considerable 
to Warrant the’ ‘ containing these principles in the 
Proportions indicated, and united with as much metallic iron as we know to exist 
: State of an oxide in the generality of lavas, would form an aggregate pos- 
ol, Xixvur, No, 1.—July, 1839, bis. li 
