360 PROFESSOR CONNELL ON THE REACTION 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 
potash 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 their 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 effer- 
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 
waters, 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 Curistison informs me that moss-water is not precipitated by acetate of lead. This, I have 
no 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 
the precipitate. Dr Witson mentions that fluoride of barium is less soluble in acids than carbonate or 
phosphate of barytes. 

