80 Reply of Dr. Dauheny to Prof. Bischof. 



4th Objection. — The evolution of carbonic acid by volcanos is 

 not explained, and these disengagements 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, Eifel,&c.,) con- 

 tains but little atmos[ heric air. 



Ansiver. — 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 j^roduce 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 |)roportion 

 of common air, tliough, 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 volcanos 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 air 

 had been robbed of its oxygen, by the inflammable bodies pres- 

 ent, may reach the air either in a separate condition, or united 

 with hydrogen in the form of ammonia. The former I have 

 generally found to be the case in thermal springs connected with 

 volcanos in an extinct or languid condition — the latter in the cra- 

 ters or fumaroles of those still in a state of greater or less activ- 

 ity. I do not wonder, therefore, that Boussingault should have 

 rarely detected nitrogen in the volcanos of the equator,* but I 

 should expect that sal-ammoniac 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 

 volcano, so that the occasional absence of nitrogen seems less 

 difficult of explanation in accordance with the chemical theory, 



* In two instances it was present. 



