OF ARTS AND SCIENCES. 



73 



" Variation in some of the properties of the Cochituate water might 

 be expected to take place. First, in the percentage of organic matter. 

 Second, in temperature. Third, in percentage of salts. 



" The effect of increasing the percentage of organic matter is ex- 

 hibited in the following table. 



" Table XIII. — Experiments with Lead in graduated Solutions 

 of Organic Matter ( Tannin) in Cochituate Water. 



" The bars of the third and fourth columns became more or less 

 coated with a loose reddish-brown coat of organic matter and lead. 

 The influence of increased organic matter of this form (which is as 

 nearly allied to the vegetable matters that might be expected to occur 

 in lake water as could be readily found) was to lessen the action on 

 lead. The organic matters of lake and river waters consist of living 

 and deceased organisms, animal and vegetable, and of soluble substan- 

 ces derived from decaying vegetation. When exposed a sufficient 

 length of time, these matters become thoroughly inorganic. The car- 

 bon becomes carbonic acid, and the hydrogen becomes water, by the 

 consumption of oxygen in solution in the water. 



" My experiments have shown, that, if the quantity of organic mat- 

 ter, such as the extract of bark, be more than yij^^j^y of the weight of 

 the water, precipitates of the organic matter in combination with oxide 

 of lead, if any is in solution, will take place. This is one of the meth- 

 ods frequently resorted to for separating organic bodies from solutions.! 



* A kind of fungous or flocculent mass fell with the lead, augmenting the vol- 

 ume of the precipitate. 



t This precipitate is visible in Croton service-pipes five years in use. It occurs 

 in the Jamaica service-pipes in Boston, and, I have been informed, in those of 

 Fairmount water in Philadelphia. 



VOT,. II. 10 



