196 Proceedings of the Boyal Society of Edinburgh. 



of lead is added to the transparent and colourless water of springs, 

 wells, and rivers, a more or less dense white cloud is almost inva- 

 riably produced. This reaction has been usually attributed to the 

 presence of inorganic salts, such as carbonates, sulphates, aud mu- 

 riates ; but it will be found that, generally speaking, this precipi- 

 tate is formed even after the water has been boiled ; that it is usually 

 dissolved by the speedy addition of a drop or two either of acetic or 

 of nitric acid, without visible effervescence; and that the agency of 

 the water with nitrate of silver is commonly too small to admit of 

 its being caused by any muriate. These facts exclude the idea that 

 it is due in the general case to carbonates, sulphates, phosphates, or 

 muriates ; although, of course, in those particular cases where the 

 water has enough of such constituents to affect acetate of lead, the 

 reactions will be modified accordingly.. Thus, in some cases, where 

 the first action is as above stated, a deposition takes place after a 

 certain interval, of sulphate of lead, no longer soluble in weak 

 acids. 



It occurred to the author that the true cause of the reaction was 

 to be found in the presence of organic matter in the water, derived 

 from the decomposition of vegetable matter in the strata or soil 

 through which it had passed. To ascertain whether this view was 

 correct, the precipitate by acetate of lead from several quarts of the 

 town w^ater of St Andrews was decomposed by sulphuretted hydro- 

 gen. After filtration, a liquid was obtainel, which, besides sul- 

 phuric acid derived from precipitated sulphate of lead, was found 

 to contain some organic matter apparently of an azotised nature ; 

 but its amount was too small to characterise its properties with ac- 

 curacy. The salt obtained by saturating the liquid with potash, 

 yielded by distillation empyreumatic vapour, and left a black coaly 

 mass behind. The liquid itself, when neutralized and sufficiently 

 diluted, had still a marked action on lead salts; and it or its potash 

 salt produced more or less precipitate after the interval of a day or 

 two, in acetate of copper and neutralized persulphate of iron. 



The author has found this matter in the town waters of Edin- 

 burgh and Glasgow, but to a less extent than in that of St Andrews. 

 The Glasgow water shewed the least of the three. He has also 

 found it more or less in every instance he has hitherto tried of 

 transparent and colourless well, spring, or river water. In rain- 

 water it does not exist, and probably could not be found in springs 

 above the limits of vegetation, or in snow or glacier water. It 

 would seem that it ought to perform functions of some importance 

 in the economy of nature, as contributing in a certain degree to 

 the nourishment of plants and even of animals. 



