{ 357 ) 



XXIII. — On the Reaction of Natural Waters with Soluble Lead Salts. By Arthur 

 CoNNELL, Esq., F.R.S.E., Professor of Chemistry in the University of St Andrews. 



(Read 19th January 1846.) 



In a former communication to the Society, I noticed a reaction presented 

 by all spring, well, and river waters which I had examined, that, even after 

 being boiled, they yielded, with acetate of lead, a precipitate readily soluble, in 

 whole or in great part, in acetic acid. This easy solubility in acetic acid shewed 

 that the precipitate was neither a sulphate nor a phosphate, and the comparative!}^ 

 slight action of nitrate of silver proved that it was not a chloride. There seemed, 

 therefore, to remain only the conclusion that it was either a carbonate, or was due to 

 organic matter. The former alternative, of course, depended on whether the solu- 

 tion in acetic acid was attended with effervescence or not; and as this seemed usually 

 not to be the case, and as, on decomposing some of the precipitate by sulphuret- 

 ted hydrogen, some organic matter in solution was obtained, the conclusion seemed 

 to be, that the appearance was caused by organic matter, probably of the nature 

 of the crenic and apocrenic acids of Berzelius. I have since, however, found that 

 by very careful observation, effervescence may be noticed during the solution of 

 the precipitate more frequently than I at first supposed. It is not so easy as 

 might be imagined to determine this point. If acetic acid is added before the 

 precipitate has subsided, no effervescence can be noticed, in almost any case, from 

 the water dissolving the carbonic acid evolved and diffused through the whole 

 liquid. And even when allowed to subside, and the greater part of the liquid is 

 decanted, the addition of acetic acid not unfrequently causes solution without 

 apparent effervescence. The cautious addition, however, of a heavier acid, such 

 as the nitric or even the muriatic, after allowing the lead precipitate to collect at 

 the bottom, and decanting the greater part of the liquid, seldom fails to shew the 

 effervescence where a carbonate is really present. 



In so far, then, as the precipitate is dissolved by acids with effervescence, we 

 may conclude that it has been caused by some carbonate remaining dissolved 

 after boiling the water ; and in so far as the solution may not exhibit efferves- 

 cence, we may conclude that it is due to organic matter, provided silver salts do 

 not indicate the presence of a sufficient quantity of chlorides, and provided acetic 

 acid instantly causes solution in whole or great part. In some instances I have 

 found that acetate of lead does not yield a precipitate, unless the water has been 

 previously boiled, a circumstance obviously due to excess of carbonic acid retain- 

 ing the carbonate of lead in solution. In regard to chlorides, I have never met 



VOL. XVI. PART III. 4 X 



