CATARACTS, AND INUNDATIONS. 09 



gges the muriatic gas, known by* its smell and white vapour, when 

 the salt under examination contains that acid. This may likewise 

 be known by dissolving the whole residue in water, and adding a 

 few drops of the nitric solution of silver. The nature of the base, 

 which, as we have observed, is either lime, magnesia, or both toge- 

 ther, is known by the name of the sulphuric acid, by a similar pro. 

 cess with that already explained respecting the acetous solution. 



3. The water used in washing the first residue of the mineral wa- 

 ter, performed, as before directed, with eight times its weight of 

 cold distilled water, contains neutral alkaline salts, such as sulphat 

 of soda, muriats, or marine salts, carbonat of potash, and of soda, 

 and sulphat of magnesia : a small quantity of sulphat of iron is 

 sometimes found. These salts never exist altogether in waters: 

 the sulphat of soda, and the carbonat of potash, are very seldom 

 found ; but marine salt is frequently met with, together with car- 

 bonat of soda. The sulphat of magnesia is likewise frequently met 

 with, and some waters even contain it in considerable quantities. 

 When the first washing of the residue of a mineral water contains 



o 



only one kind of neutral salt, it may easily be obtained by crystal- 

 lization, and its nature ascertained from its form, taste, and the 

 action of fire, as well as that of the re-agents: but this case is very 

 rare, for it is much more usual to find many salts united in this lixi. 

 vium. They must therefore be separated, if practicable, by slow 

 evaporation ; but as this method does not always perfectly succeed, 

 however carefully this evaporation be conducted, it will be neces- 

 sary to re-examine the salts obtained at the different periods of the 

 evaporation. Carbonat of soda is usually deposited confusedly 

 with the muriatic salts, but they may be separated by a process, 

 pointed out by M. Gioanetti. It consists in washing this mixed 

 salt with distilled vinegar; for this acid dissolves the carbonat of 

 soda. The mixture must then be dried and washed a second time 

 with alkohol, which takes up the acetit of soda, without acting on 

 marine salt. The spirituous solution being evaporated to dryness, 

 and the residue calcined, the vinegar becomes decomposed and 

 burns. Soda alone remains, whose quantity may be then accurately 

 determined. 



4. The water used in the quantity of four or five hundred times 

 the weight of the residuum of the mineral water contains only sul- 

 phat of lime. This may be ascertained by pure caustic ammoniac, 



VOL. HI. P 



