On Sal Nitrum and Nitro- Aerial Spirit i8i 



penetrated in some places by pores of a kind 

 suitable for the passage in dense numbers of aerial 

 particles, and for sucking them in, as it were. For 

 since the aerial particles, carried to the saline-sul- 

 phureous mineral and effervescing with it, are swept 

 away by the streams of water flowing thence, the 

 result is that the nearest pvarticles of air are forced by 

 atmospheric pressure into the place of those carried 

 away, while these also are soon absorbed and followed 

 by others ; and thus aerial particles come to the 

 effervescing mineral in a continual stream. 



Perhaps the lofty hills, with deep and abrupt 

 valleys between, which engirdle Bath on all sides, 

 contribute somewhat to the entrance of aerial particles 

 into the ground and to the maintenance of the heat 

 of the thermal waters. For, in consequence of this, 

 the air thrown back from the hills, and reflected in 

 various directions in the valleys, strikes forcibly 

 against the ground and is thrust into it. 



It is a further proof of the views set forth, that the 

 Bath waters contain a saline-sulphureous mineral, 

 which seems not very unlike those marchasites from 

 which vitriol is made ; and indeed the sand of the baths, 

 if exposed for some time to the air, will effervesce and 

 turn into vitriol. But the reason that the salts of the 

 said thermal waters are of an acido-saline nature 

 seems to be, that when the saline-sulphureous mineral 

 effervesces in the manner already described, some of 

 the saline particles are brought to a certain fluidity, 

 as was previously remarked. But these salts, when 

 thus liquefied, unite with the other salts which are of 

 an alkaline nature, and from these, combined with 

 one another, a certain acido-saline salt is composed. It 

 is, however, only an immature salt, since it is swept 

 away, while not yet duly fermented nor brought to 



