50 Mr. H. iMedlock on the Reciprocal Action of Metals 



poses water, and forms again quadribasic nitrite of lead and am- 

 monia. 



In the decomposition of the quadribasic nitrite of lead, much 

 of the )nonobasic nitrite is carried down with the precipitated 

 carbonate of lead*. As there is a constant daily accession of 

 new organic matter in a state of decomposition to our cisterns, 

 and as similar changes to those above described are constantly 

 going on, and may under special circumstances be suddenly in- 

 creased, it will be evident that tlie use of leaden cisterns exposes 

 us to the danger of having lead dissolved in our water in doses 

 which may sometimes rise to poisonous proportions. 



Having established, as I believe by most conclusive experi- 

 ments, the remarkable reaction which takes })Iacc between lead 

 and the organic matters contained in water, I was induced to 

 study more fully some singular phjenomeua I had previously 

 noticed, which become apparent when water remains for a few 

 hours in contact with a large surface of iron. 



In September 1856, I was requested by the Directoi-s of the 

 Amsterdam Water Company to analyse several samples of water 

 from the city of Amsterdam. Complaints of the water had been 

 made by many of the inhabitants. The water possessed a peculiar 

 fish-like odour ; and altliough perfectly transparent and colour- 

 less,and free from the slightest chalybeate taste, it was found, after 

 standing, to deposit a reddish-brown sediment, which coated every 

 vessel in which the water was allowed to remain for a few hours. 



The service-pipes being of iron, the deposit was assumed to 

 consist of the sesquioxide, resulting cither from the decomposi- 

 tion of a protosalt of iron in solution, or from the attrition of the 

 iron pipes through which the water is conveyed. 



I may here observe that Amsterdam is supjdied with water 

 from the "Duins" (sand-hills) in the neighbourhood of Haarlem. 

 Trenches five miles in length have been dug on the sides of the 

 hills to intercept the rain-fall. The water is conveyed to a large 

 reservoir, whence it flows to the filter-beds at the works, and 

 there filtered through 4 feet of filtering medium, consisting of 

 pebbles, shells, and fine sand. After filtration it is pumped up 

 an iron stand-pipe, 150 feet high, and conveyed thence by iron 

 mains to Amsterdam, a distance of eighteen miles. 



Five sanqjlcs of the water were sent to mc for analysis; one 

 from tli(! works before the water came in contact with iron, the 

 other four from various stand-pipes in the city. 



In the water from the works, before it came into contact with 



* In investigatiiifj the nitrites iind hyponitrates of lead, I found the car- 

 bonate of lead precipitated by riirlionic acid from any of the basic salts, to 

 require long-continued wasiiing to remove every trace of the soluble neu- 

 tral salt. 



