071 Sal Nitrtim and Nitro-Aerial Spirit 171 



earth, adheres almost everywhere to the bottom of 

 the channels by which the waters are carried off. 



From what has been said, it may be inferred that 

 the thermal waters of Bath are impregnated with a 

 certain acido-saline salt. And indeed this salt of the 

 thermal waters does not seem to be very unlike 

 vitriolated tartar or aluminous salt. But the reason 

 why these salts do not destroy each other, but that 

 each of them effervesces with a salt opposed to it, will 

 be to some extent intelligible from what was said in 

 the previous chapter. For the said salts are so 

 imperfect that they are not able to destroy each other 

 entirely when they combine together. But there will 

 be a fuller discussion of these salts afterwards. 



As for nitre and sulphur, with which it has been 

 hitherto supposed that the Bath thermal waters are 

 impregnated, I think that neither of them exists 

 dissolved in the water of these springs. 



That nitre does not exist in them is evident, 

 because if the salts which remain after evaporating 

 the water of the baths are placed on burning charcoal, 

 they in nowise deflagrate like nitre. However, I 

 will not deny that the immature salts of an alkaline 

 nature (with which the mud and sand of the baths are 

 imbued) may, perhaps, if exposed for some time to the 

 air, be changed by its influence into nitre. 



As to sulphur, which is so often said to be present 

 in nearly all thermal springs, my opinion is that it 

 does not exist dissolved in these waters. For if a 

 solution of alum, or of vitriol, or any other salt, 

 whether acid or fixed, is mixed with the water of 

 these thermal springs, the precipitation of sulphur is 

 not at all indicated either by a fetid odour or by any 

 other sign. And yet that always happens in solution 

 of sulphur made in the water in which quicklime has 



