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XXIV. On the Precipitate produced in Spring and River Waters 

 by Acetate of Lead, By A. Connell, Esq., Professor of 

 Chemistry in the University of St. Andrews*. 



^V^YLYj white precipitate which it is well known is usually 

 JL produced in spring and river waters by acetate of lead, 

 has been commonly attributed to the presence of sulphates, 

 chlorides and carbonates. The comparatively trifling action 

 of silver salts, however, shows that it is very rarely, unless in 

 the case of what are called mineral waters, due to chlorides ; 

 and the ready solubility of the precipitate in acetic acid in 

 whole or in great part, proves that it is not due to sulphates 

 or phosphates, except in so far as it may be insoluble in acetic 

 acid. Carbonates therefore remain as the probable cause ; 

 and this is established by the circumstance, that although 

 effervescence cannot be noticed on the immediate addition of 

 acetic acid, effervescence will be observed if the precipitate is 

 allowed to subside, and the greater part of the solution de- 

 canted, and an acid then added. 1 have found on investiga- 

 tion that carbonate of lime is the usual source of the reaction. 

 The remarkable fact however on this view is, that the reaction 

 is scarcely diminished by boiling and filtering the water; and 

 indeed in some instances does not take place unless these steps 

 are had recourse to, and acetic acid still dissolves the whole 

 or great part. If the waters referred to are boiled and filtered 

 and then largely concentrated by evaporation, they usually 

 deposit carbonate of lime, and do not indicate any such alka- 

 line reaction as shows an alkaline carbonate. The carbonate 

 of lime causing the reaction is therefore evidently held dis- 

 solved in the water independently of the presence of free 

 carbonic acid ; and I do not think that chemists, generally 

 speaking, are aware that common water may still retain enough 

 of carbonate of lime to give, with acetate of lead, a consider- 

 able precipitate of carbonate of lead, although they may have 

 been boiled and filtered. If in any such case the precipitate 

 should be found to dissolve in acetic acid truly mthout effer- 

 vescence, the probable cause would be the presence of a suffi- 

 cient quantity of some organic matter, such as crenic or apo- 

 crenic acid, which precipitates lead salts ; for it is not the least 

 likely that fluorine, which has been found in some spring 

 waters, should ever be present in sufficient quantity to affect 

 lead salts, and fluoride of lead would very likely not be so- 

 luble in acetic acid. 



The question then arises, whence proceeds this carbonate 



* Communicated by the Author. 



