Chap. 8.] Mineral Waters. 511 



upon mere accurate examination, are found to afford 

 it. The waters generally called fulphureous or hepa- 

 tic, are only impregnated with fulphureous or hepatic 

 gas, which is a folution of fulphur in inflammable: air. 

 This is the fame gas which riles from liver of fulphur, 

 and liver of fulphur itfelf has been detected in a very 

 minute quantity in mineral waters. Sometimes bitu- 

 mens are met with in mineral waters, and commonly 

 make their appearance on the furface. 



7. Metals. Of thefe iron is moft frequently found 

 in water, fometimes copper, and more rarely zinc. 

 Waters which contain iron are called chalybeates, and 

 are very common. 



It was formerly imagined that iron was fufpended 

 in mineral waters by means of the vitriolic acid ; but 

 M. Monnet has afcertained, that very few of them 

 contain vitriolic acid, and that the carbonic acid, or 

 fixed air, is almoft the only medium by which the iron 

 is fufpended. The carbonic acid is fometimes in 

 cxcefs, fo as to render the chalybeate water acidulous, 

 in other inftances it fufpends the iron without being 

 in excefs. Chalybeates may, in general, be. known 

 by the yellow ochry fediment depofited in their courfe, 

 and alfo by ftriking a purple colour with decoction of 

 galls. 



In examining any mineral waters, the firft object of 

 attention is, to have the water as frem as poflible, 

 fince, if it contains any volatile matters, they will foon 

 fly off. A great number of trials are therefore to be 

 made on the fpot. The contents of the neighbouring 

 flrata, particularly of any high ground, from which the 

 water feems to proceed, are alfo to be regarded, as 

 they often ferve to account for the properties of mi- 

 neral waters. 



One of the moft obvious circumftances to be at- 

 tended 



