130 THE CHEMISTRY OF CREATION. 



decompositions possess interest. It appears more 

 than probable that the true source of this gas, 

 in the first case, in volcanic districts, is that 

 simple decomposition which heat effects upon 

 limestone, whereby a portion of its carbonic 

 acid is discharged, a decomposition precisely 

 similar to that we effect in burning limestone, 

 the gas of which has so often proved fatal to 

 the incautious traveller. The intense heat of an 

 eruption must affect all adjoining rocks ; and it 

 is presumed that the calcareous or limestone 

 rocks, heated by this means, expel their carbonic 

 acid, and produce the phenomenon in question. 

 We have the authority of Dr. Daubeny for this 

 supposition. There is less difficulty in disco- 

 vering the source and mode of production of 

 the gas in the latter case. In the chemical de- 

 compositions which accompany the formation 

 of brown coal, carbonic acid is extracted from 

 the substance of the wood. The same process 

 appears to be continually taking place at great 

 depths in all the layers of wood coal, sometimes 

 rendering mines unavailable from its abundance 

 in the form of what miners call "choke-damp." 

 Water percolating through the soil to these 

 strata, and meeting with the gas, dissolves it, 

 and rises to the surface as an acidulous carbon- 

 ated spring. 



But, from whatsoever source proceeding, this 



