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I. AERIAL MATTERS. 



1. Mephitic, fixable, or fixed air^ is 

 heavier than common, or vital air, and fre- 

 quently mixed with water; by which union, 

 common water is capable of diffolving iron, and 

 thereby forming a chalybeate fpring, as in Pyr- 

 mont, Spa, and many other celebrated mineral 

 waters (y). 



This mephitic air is detected by lime-water, 

 the former precipitating the calcareous earth of 

 the latter in a white powder. To difcover the 

 quantity of this aerial matter, a bottle filled 

 with the mineral water mould be tied over the 

 mouth with a loofe bladder : the bottle is then 

 to be placed in boiling water, the heat whereof 

 will extricate the mephitic air, which riling into 

 the bladder, may be collected by tying the blad- 

 der clofe to the neck of the bottle, and after- 

 wards meafured by a proportionable bulk of 

 water. (See Sect. V.) 



II. SALINE BODIES. 



1. An acid is fometimes found in the com- 

 pofition of mineral waters, which is always the 

 vitriolic. 



a. In its fixed ftate, which is fuppofed to be fe- 

 parated from pyrites : this is however very rare, 

 and probably never occurs, as it cannot remain 

 long in this ftate, without being neutralized by 

 earths, falts, or metals. 



(a/) This was noticed many years ago by Dr. Black in 

 his ledtures, and has fince been adopted by feveral ingeni- 

 ous writers. 



Many 



