Reply of Dr. Daubeny to Prof. Bischof. 79 
ing outwards to protrude the liquid lava to so great a height, and 
as this pressure continues for many years, during which time the 
phenomena by no means abate in activity, it is impossible that 
air should in any way contribute to it. 
Answer.—The very conditions of our theory imply the exist- 
ence near and about the focus of the voleano of vast caverns, 
caused originally by the heaving up of the softened rocks, owing 
to the elastic vapors disengaged, and consequently filled in the 
first instance by these matters. But the amount of these vapors 
must be undergoing continual oscillation. Ist, Owing to differ- 
ences of temperature caused by the constantly varying intensity 
of the volcanic action. 2dly, By the reaction of the gases upon 
each other, as for instance, sulphuretted hydrogen upon sulphu- 
rous acid, muriatic and ca:bonic acids upon ammonia, the fixed 
alkalies and the earths. 3dly, By the ever-varying proportion 
between the amount of water decomposed by the alkaline or 
earthy metals, and generated by the union of hydrogen to the 
oxygen present. Hence, unless the passages between these cav- 
erns and the external atmosphere were hermetically sealed (which 
nO one contends), air must at times enter the latter to fill the 
vacuum thus occasioned. 
3d Objection.—If the oxidation of the earthy and alkaline 
Metals were to take place at the expense of water, enormous 
quantities of hydrogen would be evolved, which has never been 
observed. 
Answer.—Hy drogen could hardly be expected to escape in 
afree state from a spot which contained so many elements for 
Which it possesses a strong affinity, and to which it would be 
Presented under the influence of the pressure and temperature 
80 well calculated to promote its combination with them. 
; Thus, sulphur and chlorine we know to be generally present 
iN voleanos, and oxygen and nitrogen, we may fairly assume to 
80. But, although hydrogen may not be disengaged alone, 
large quantities of it, in combination with sulphur, appear to be 
almost universally evolved from volcanos, and it is probable that 
the great beds of sulphur which exist in most volcanic districts 
(viz. Sicily) are the result of the decomposition of the sulphuret- 
ted hydrogen evolved. Nor, indeed, does it seem possible to ex- 
Plain the presence of this hydrogen, without having recourse to 
the chemical theory. 
