72 On Mineral Waters, 



employ in the production of carbonic acid gas, would exceed the 

 limits of this paper. We shall content ourselves with observing, 

 that, for chemical reasons, its creation out of its elements is 

 far from probable ; as it must, in that case, necessarily come 

 forth, adulterated with azote, carbonic oxide, or even with em- 

 pyreumatic oil. Hence, in the volcanic laboratory, it can only 

 be produced by a decomposition of the carbonates — ^which may 

 be effected by a variety of processes, conformable with the laws 

 both of geology and chemistry, but which we have not here 

 room to specify. 



The probability, however, is, that these processes vary, ac- 

 cording to the different features of the soil ; but that the deve- 

 lopment most commonly results from the ignition of carbonate 

 of lime — the decomposition of which requires less heat, when 

 it is brought into contact with steam or silica. 



It might perhaps be expected, that where carbonic acid gas 

 is thus produced in large quantity, its temperature should ne- 

 cessarily be elevated ; and the Vesuvian grottos receiving this 

 gas have been ascertained, by Messrs. Monticelli and Covelli, to 

 exceed in temperature, by 4i degrees, the grottos which con- 

 tained it not. 



The very general occurrence of carbonic acid gas throughout 

 the globe, proves that Nature has other means for its production 

 in smaller quantities. Dr. Struve has found that carbonic acid 

 gas is disengaged by bringing carbonate of lime in contact with 

 silicate of alumina and water, at common temperatures, though 

 more readily if the latter be heated. To this process of de- 

 velopment, common spring water is perhaps indebted for its 

 small portion of this gas. 



With regard to the acids in the sulphates and muriates of 

 mineral waters, where the surrounding rocks yield only the 

 respective bases, volcanic action seems to be the principal 

 agent in their production. To notice all the facts, however, 

 which appear to favour this or other hypotheses, would spin 

 out the present paper to far too great a length. They have 

 been collected and revised in an elaborate work, by Professor 

 G. Bischoff, of Bonn*. 



* Die Yulkanischen Mineralquellen Deulschlands und Frankreichs, deren 

 UrspruBg, Mischung; und Verbfleltnisse zu den Gebirgsquellen, 1826. 



