:36() PROFESSOR COXXELL OX THE REACTIOX OF NATURAL WATERS 



alkaline matters. This was, accordingly, done in numerous instances by ordi- 

 nary methods. Although the potash or soda present may have been originally 

 dissolved as a carbonate ; yet we, of course, ultimately obtain it on evaporation, 

 as a chloride or sulphate, through double decomposition with the lime or magne- 

 sian salts present ; or through the stronger affinity of the acids of these salts, if 

 their earths have been previously removed by chemical means. In no instance of 

 a natural water which gave the reaction with lead salts, did I fail to detect either 

 jjotash or soda, or both ; and it ought to be recollected that a very minute quan- 

 tity of either is sufficient. It will be found that one drop each of solutions of car- 

 bonate of potash, of sulphate of magnesia, and of chloride of calcium, added to 

 several ounces of distilled water, will produce the reactions referred to with lead 

 salts and acetic acid. 



If these views are well-founded, it is evident that lead salts become a pro- 

 bable indication, at least where then- effect is considerable, of the presence of 

 alkalies in natural waters. And, in general, we may conclude, that if after boil- 

 ing, and filtration if necessary, any water yields a considerable cloud with acetate 

 of lead, readily soluble by adding a drop or two of acetic acid, the cause will be 

 either carbonate of lime, probably due to double decomposition, or it will be 

 organic matter, if any such matter precipitable by lead salts is present in suffi- 

 cient quantity.* In so far as it is dissolved by an acid, after subsidence, with 

 effervescence, it will be due to the former cause ; in so far as, without effei"- 

 vescence, to the latter. 



It seems, at all events, evident from the experiments which have been de- 

 tailed, that the carbonate of lime present has not owed its presence to the solvent 

 agency of carbonic acid, even when first taken up. 



It is plain, that the carbonate of lime thus held dissolved by spring waters, 

 from whatever source it may be obtained, must be of considerable importance in 

 the economy of nature in furnishing a supply, through the intervention of these 

 w^aters, of that lime which is so essential a constituent, in its various states of 

 combination, of the inorganic portion of plants. This will hold whether such 

 waters are applied to the land in the way of irrigation, or by the more slow pro- 

 cesses of natural infiltration. 



* Dr Christison informs me that moss-water is not precipitated by acetate of lead. This, I have 

 110 doubt is a correct observation ; but still other states of organic matter may occasion a precipitate. 

 The crenic and apocrenic acids are both known to precipitate lead salts. 



Although fluorine is now known to be occasionally present in ordinary natural waters, and although 

 fluoride of lead is sparingly soluble in water, yet I am not aware that fluorine is ever present in such 

 quantity in such waters as to affect lead salts ; and, if it were, acetic acid might very likely not dissolve 

 till' precipitate. Dr Wilson mentions that fluoride of barium is less soluble in acids than carbonate or 

 l>hosphate of barytes. 



