CATARACTS, AND INUNDATIONS. 



'be referred, and direct the method or* analysis. 3. The deposi. 

 tions formed at the bottom of the basons, the substances which 

 float on the water, and the matters which rise by sublimation, 

 form likewise an object of important research, which must not be 

 neglected. After this preliminary examination, the proper analysis 

 may be proceeded on, which is made after three methods, by re- 

 agents, by distillation, and by evaporation. 



Ike Examination of Mineral Waters, by Re-agents. Those 

 substances, which are mixed with waters, in order to discover the 

 nature of the bodies, held in solution by such waters, from the phe- 

 nomena they present, are culled re-agents. 



The best chemists have always considered the use of re-agents 



J O 



as a very uncertain method of discovering the principles of mineral 

 "v liters. This opinion is founded on t):e considerations that their 

 effects do not determine, in an accurate manner, the nature of the 

 substances held in solution in waters; that the cause of the changes 

 which happen in fluids by their addition is often unknown : and that 

 in fact, the saline matters usually applied in tins analysis are capable 

 of producing a great number of phenomena, respecting which it is 

 often difficult to form any decision. For these reasons, most che- 

 mists who have undertaken tin's analysis, have placed little depend- 

 ence on the application of re-agents. They have concluded, that. 

 evaporation aiibrds a much surer method of ascertaining the nature 

 and quantity of the principles of mineral waters ; and it is taken for 

 granted, in the best works on the analysis of the^ fluids, that re- 

 agents are only to he used as secondary means, which at most sevve 

 Jo indicate or afford a probable guess of the nature of the princi- 

 ples contained in waters; and for this reason, modern analysis 

 have admitted no more than a certain number of re. agents, and 

 have greatly diminished the list of those used by t/ke eaviier che- 

 mists. 



But it cannot be doubted at present, that the heat required tn 

 evaporate the water, however gentle it r.iay be, must produce sen- 

 sible alterations in its principles, and change them in such a manner, 

 as that their residues, e.xaiyined by the' different methods of chc 

 mistrv, shall y fiord compounds differing from those which were 

 originally held in solution in the water. The loss of the gaseous 

 Mibst;mces, which frequently are the principal agents in mineral wa- 

 ters, sir.^-jlarly diangts llieir nature, and besides causing a prtcij>j- 



