CATARACTS, AND INUNDATIONS. 2O3 



has been done by Messrs. Bergman and Gioanetti. The products 

 which the nitric solutions of silver or mercury afford when mixed 

 with mineral waters, deserve particular attention. It is more par. 

 ticularly necessary to operate with laro;e quantities of water, when 

 these re-agents are used, in order to determine the nature of the 

 acids contained in the waters. The analysis of these fluids will be 

 complete when their acids are known, because tiiese are often com- 

 bined with the basis exhibited by the re-agents before-mentioned. 

 The colours, the form, and the abundance of the precipitates af- 

 forded by the nitric solutions of mercury and silver, have hitherto 

 exhibited to chemists the nature of the acids which caused them. 

 A tiiick and ponderous deposition immediately formed by tiie.se 

 solutions, denotes the muriatic acid : if it i small in quantity, 

 white, and crystallized with the nitrat of silver, or yellowish, and 

 yellow and irregular when formed with that of mercury, and if it 

 subside but slowly, it is attributed to the sulphuric acid. But as 

 these two acids are often met with in the same water, and as 

 alkali and chalk likewise decompose the solutions, the results or 

 deductions made from the physical properties of the precipitates 

 must be uncertain. It is therefore necessary to exanvne them more 

 effectually : for this purpose, solutions of silver or of mercury may 

 be mixed with five or six pounds of the water intended to be ana- 

 lysed. The mixtures being filtered, twenty four hours after the 

 precipitates must be dried, and treated according to the methods 

 of chemistry. If the precipitate afforded by tiie nitric solution of 

 mercury be heated in a retorr, the portion of metal umied with 

 the muriatic acid of the waters will be volatilized into mercurius 

 duicis, and that which is combined with the sulphuric acid will re- 

 main at the bottom of the vessel, and exhibit a reddish colour. 

 These tno salts may likewise be distinguished by putting them on a 

 hot coal ; the sulphat of mercury, if present, emits a sulphureous 

 acid, and assumes a red colour; the mercurial muriat remains 

 white, and is volatilized without exhibiting any smell of sulphur. 

 These phenomena likewise serve to distinguish the precipitates 

 which may be formed by the alkaline substances contained in water, 

 since the latter do not emit the sulphureous smell, and are not 

 volatile without decomposition. 



The precipitates produced by the combination of mineral 

 waters with the nitric solution of silver, may be as easily examined 



