Mineral Waters. 271 



earth will be re-dissolved. If a considerable 

 quantity of earth is obtained by precipitation, 

 it will be easy to learn of what sort it is, by 

 allowing it to settle in a tall vessel, pouring off 

 the water, and then adding to it the sulphuric 

 acid. If it is lime, it will effervesce, and form 

 an insoluble gypsum, or selenitic compound. 

 If it is magnesia, it will effervesce, and unite 

 with the acid into sulphate of magnesia, which 

 we may know by its dissolving in the sulphuric 

 acid, and its bitter taste. If it is alumina, it 

 will effervesce, and unite with the acid into an 

 astringent and sweetish solution, in fact, into 

 alum. 



Sulphur must be combined with an alkali or 

 calcareous earth to keep it dissolved in water: 

 when combined with fixed alkali, or quick-lime, 

 it is easily separable by an acid ; for the sulphur, 

 being suspended by the alkali, subsides when the 

 acid unites to the alkali. Many sulphureous 

 waters are either muddy at first, or very soon 

 become so. 



Metallic substances are very common in mi- 

 neral waters in a state of combination with acids. 

 Macquer has given an experiment to discover 

 this ; he found that the prussiate of potass, or 

 prussian alkali, as it has been called, if saturated 

 with the matter it receives in its operation, has 

 no attraction for acids, and consequently pro- 

 duces no disturbance in a solution of lime and 

 acid ; it is only the solutions of metals which are 



