Water. . 259 



clrogen gas is, however, the chief ingredient in 

 those waters which are called sulphureous. 



3. The boracic acid has been observed in some 

 lakes in Italy. 



III. An alkaline salt is sometimes met with 

 in water. This is generally soda. Some expe- 

 riments of Margraff upon waters of particular 

 wells seem, indeed, to show that they contain 

 potass, either separate or combined. Some 

 writers mention a volatile alkali in mineral wa- 

 ters. It is true, that whenever a union of nitro- 

 gen with hydrogen can be effected, volatile 

 alkali may be produced, but from the volatile 

 nature of the compound the phenomenon must 

 be extremely rare. 



IV. Neutral salts. 



1. The sulphats are frequently found in mi- 

 neral waters, especially sulphat of soda, and still 

 more commonly, sulphat of lime and magnesia. 

 The latter, formerly known by the name of 

 Epsom salt, is almost always an ingredient in 

 those waters which have purgative qualities; in 

 truth, its old name was derived from its being so 

 abundant in the mineral springs near Epsom. 

 Sulphat of ammonia is found in the neighbour- 

 hood of volcanoes. Alum is a rare ingredient ; 

 sulphat of iron is not very common ; and sul- 

 phat of copper is only found in waters which 

 isue from copper-mines. 



2. Nitre is very uncommon; and, indeed, so 

 are all the nitrats : that of lime has been found 



