CATARACTS, AND INUNDATIONS. 



Because chalk, or Spanish white, contains magnesia and river water: 

 lie divided this solution into two parts ? into the first he poured a 

 few drops of very pure sulphuric acid, recently made, and very 

 caustic; this he put into a well-closed bottle: at the end of twenty- 

 four and forty-eight hours it was clear and transparent, without any 

 precipitate, and therefore no decomposition had taken place. Tle 

 second portion was treated in the same manner with ammoniac, but 

 placed in a vessel which communicated with the air by a large aper- 

 ture : at the end of a few hours a cloud was formed near the upper 

 surface, which continually increased, and was at last precipitated to 

 the bottom. This deposition effervesced strongly with sulphuric 

 acid, and formed sulphat of lime. The carbonic acid contained In 

 this precipitate was therefore afforded by the ammoniac which had 

 attracted it from the atmosphere. This combination of carbonic 

 arid and ammoniac forms ammoniacal carbonat, capable of decom- 

 posing calcareous salts by double affinity, as Black, Jacquin, and 

 many other chemists have shown, and as may be easily proved 'bj 

 pouring a solution of ammoniacal carbonat into a solution of snU 

 phat of lime, which is not rendered turbid by caustic ammoniac* 

 Lastly, to render the theory of this second experiment clearer, 

 Fourcroy took the first portion to which the caustic ammoniac had 

 been added, and which, having been kept in a close vessel, had |^t 

 no part of its-transparency* He reversed the bottle which contained 

 it, over a funnel of a very small pueumato-chcmical apparatus, * 

 by the assistance of a syphon, passed into it carbonic acid 1 gas, drs- 

 engaged from the effervescent fixed alkali by sulphuric acid* In 

 proportion us the bubbles of tins acid passed through the mixture, 

 it became turbid in the same manner as lime-water;" by (^tttion a 

 precipitate was separated, which was found to be chai^j^pthe wa- 

 ter, by evaporation, afforded ammouiacal sulphat : gaseous water, 

 or the liquii! carbonic acid, produced Uie same composition in a i }0- . 

 ther mixture of sulphat of linie, and caustic 'ammoniac. This de- 

 cisive experiment clearly shows, that ammoniac decomposes sulphat 

 of lime by double affinity, and by means of the carbonic acid* 

 Hence we sre, that when it is required to preserve a mixture of the 

 mineral water with ammoniac for several hours (which is sometimes 

 necessary, because it does not decompose certain earthy salts, but 

 very slowly), the experiment must be made in a vessel which can be 

 Accurately closed, in order to prevent the contact of air, which 



