Mineral Waters. 263 



learn the proportion of common air and of car- 

 bonic acid gas contained in any water what- 

 ever. 



Carbonic acid, when uncombined in any water, 

 will turn the infusion of litmus red. The red- 

 ness will gradually disappear, but may be restored 

 by adding more of the mineral water. 



Some doubts have been entertained whether 

 the sulphuric acid is ever found in a perfectly 

 separate state in mineral waters, for the waters 

 called acidulated derive their pungency chiefly 

 from carbonic acid. One reason that these waters 

 seldom contain this acid is, that it cannot run far 

 without meeting with some substance with which 

 it will combine. The only manner in which we 

 can imagine the sulphuric acid can be present 

 in mineral waters is, by the decomposition of 

 the pyrites, which melts into a very acid liquor, 

 containing sulphat of iron, with more acid than 

 is necessary for constituting a true sulphat: a 

 part of this will probably be separated and mixed 

 as an unsaturated acid in mineral waters ; but 

 still it will be more or less accompanied with 

 iron or alum. 



Sulphuric acid exists in waters which form 

 precipitates with the following saline solutions : 



Muriat, nitrat, or acetat of barytes, 

 Do. strontian, 



Do. lime, 



Nitrat or acetat of lead. 

 Of these the most powerful test is muriatof ba- 



