80 Reply of Dr. Daubeny to Prof. Bischof. 
Ath Objection.—The evolution of carbonic acid by volcanos is 
not explained, and these diseugagements of carbonic acid gas 
could not take place in the presence of atmospheric air in those 
vast subterranean cavities without their mixing together. Now, 
the carbonic acid evolved by volcanos (Vesuvius, Bifel, &c.,) con- 
tains but little atmospheric air. 
nswer.—The evolution of carbonic acid in countries exposed 
to the influence of volcanic heat, would seem to be a necessary 
result of the existence of calcareous matter in the rock forma- 
tions. Its continuance for so long a period after the volcano has 
ceased to be in activity, seems to show, that it is not derived di- 
rectly from the chemical processes which produce the phenomena 
in question, but is only caused by the heat which these processes 
tend to diffuse through the adjacent rocks. Hence there seems 
no reason why it should be intermixed with any large proportion 
of common air, though, as I have shown, this ingredient is rarely 
altogether absent in any samples which it has fallen to my lot to 
examine. 
5th Objection.—No nitrogen, according to Boussingault, is 
evolved from the voleanos under the equator, as would be the 
case if any process of oxydation were going on in which atmos 
pheric air co-operated. 
Answer.—The nitrogen remaining after the atmospheric aif 
had been robbed of its oxygeu, by the inflammable bodies pres- 
ent, may reach the air either in a separate condition, or unite 
with hydrogen in the form of ammonia. The former I have 
generally found to be the case in thermal spriugs connected with 
volcanos in an extinct or langnid condition—the latter in the era- 
ters or fumaroles of those still in a state of greater or less activ- 
ity. Ido not wonder, therefore, that Boussingault should have 
rarely detected nitrogen in the volcanos of the equator,* but I 
should expect that sal-ammouiac may, nevertheless, be exhaled 
from some of them. If this be not the case, it is still possible 
that the sal-ammoniac sublimed may have been accumulated 
within some of the vast cavities existing in ‘the interior of the 
voleano, so that the occasional absence of nitrogen seems less 
difficult of explanation in accordance with the chemical theory, 
Ai ee rial 
* In two instances it was present. 
| 
