CATARACTS, AND INUNDATIONS.. 



a mixed neutral salt, similar to the ammoniaco-mercurial muriat, 

 or sal alembrotk. The ammoniac does not, therefore, precipitate 

 tiie whole of the magnesia, and consequently does not accurately 

 exhibit the quantity of Epsom sail, of which that earth is the base. 

 For this reason lime-water is preferable for ascertaining the nature 

 and quantity of salts with base of magnesia contained in mineral 

 waters. It has likewise the property of precipitating the salts with 

 aluminous base much more abundantly and readily than ammoniacal 

 gas. 



The concentrated sulphuric acid precipitates a white powder 

 from water which contains barytes, according to Bergman ; but, a* 

 the same chemist observes, that this earth is seldom found in mine- 

 ral waters, it will not be necessary to enlarge on the effects of this 

 re-agent. When it produces an effervescence, or bubbles in water, 

 it indicates the presence of chalk, carbonat of soda, or pure carbonic 

 acid ; each of these substances may be distinguished by certain pe- 

 'culiar phenomena. If water containing chalk be heated after the 

 addition of sulphuric acid, a pellicle and deposition of sulphat of 

 Jime are soon formed, which does not happen with waters which 

 are simply alkaline. At first consideration it may seem that the 

 sulphat of lime ought to be precipitated as often as the sulphuric 

 acid is poured into water containing chalk ; this, however, very sel- 

 dom happens without the assistance of heat, because these waters 

 most commonly contain a superabundance of carbonic acid, which 

 favours the solution of the sulphat of lime, and of which it is ne- 

 cessary to deprive them before the salt can be precipitated. This 

 fact may be shown 4ii.lhe clearest manner, by pouring a few drops*; 

 of concentrated sulphuric acid into a certain quantity of if! me water 

 which has been precipitated, and afterwards rendered clear by tiie 

 addition of carbonic arid : if the lime-water be highly charged with 

 regenerated calcareous earth, a precipitate of sulphat of lime is 

 thrown down in a ft\v minutes, or more slowly in proportion as 

 the carbonic acid is set at liberty: Jf no precipitate he afforded by 

 standing, as will be the case when the quantity of sulphat of lime 

 is very small, and the superabundant carbonic acid considerable, the 

 application of a slight degree of heat will cause a pellicle o cal- 

 careous sulphat, and a precipitate of the same nature to be formed. 



The nitrous acid is recommended by Bergman to precipitate sul- 

 phur from hepalized waters. The experiment may be made by 



VOL. III. U 



