Reply of Dr. Dauheny 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 im['ly the exist- 

 ence near and about the focus of the volcano 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. Bat the amount of these vapors 

 must be undergoing continual oscillation. 1st, 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 caibonic acids upon ammonia, the fixed 

 alkalies and the earths. Hdly, 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. 



3(Z 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. — Hydrogen could hardly be expected to escape in 

 a free 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 

 so well calculated to promote its combination with them. 



Thus, sulphur and chlorine we know to be generally present 

 in volcanos, and oxygen and nitrogen, we may fairly assume to 

 be so. 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. 



