and the Constitue?its of Well- and River-waters. 51 



iron, the quantity of iron-oxide, alumina, and phosphates (pre- 

 cipitated by ammonia) amounted to 0-95 gr. per gallon. In 

 the four other analyses of the water, after it had passed through 

 twenty miles of iron pipes, the quantities were reduced in the 

 severa'l determinations to 009 gr., O'O? gr., 007 gr., and in the 

 fourth sample to an unweighable trace, nius, instead of taking 

 up an additional quantity of iron-oxide from the mains, the water 

 was found actually to have lost nearly the whole of that whicli it 

 previously held in solution. But notwithstanding the almost 

 entire precipitation of the iron actually in solution from the water 

 which had passed through iron pipes, this water formed the objec- 

 tionable red deposit on standing ; while the water from the works 

 holding in solution nearly half a grain of iron-oxide per gallon 

 formed no such deposit. Therefore it was a priori to be assumed 

 that the red deposit could not consist of oxide of iron, and con- 

 sequently it appeared necessary to examine this deposit very care- 

 fully. The precipitate from ten gallons of water was collected 

 in a porcelain capsule, evaporated to dryness in a water-bath, 

 and heated subsequently in an air-bath to 24-8° F. (120° C.) 

 until it ceased to lose weight. On ignition, the precipitate 

 charred and was almost entirely consumed, leaving only a minute 

 quantity of ash, consisting of silica, alumina, iron-oxide, and 

 carbonates of lime and magnesia. The small quantity of this 

 deposit at my command did not permit rae to make a quantita- 

 tive analysis thereof; but having found that the deposit con- 

 sisted almost entirely of organic matter, a portion of it separated 

 from one gallon of water was submitted to a microscopic exami- 

 nation, and found to consist of the filaments of dead and decay- 

 ing alga?, confervae, and other microscopic plants, in various 

 stages of decay, and varying in colour from green through pale 

 yellow, orange, red, brown, dark brown to black. INIany of the 

 iibres retained a perfectly organized structure, and in some the 

 sjjores were distinctly visible. Amongst these plant-remains 

 wvYv numerous siliceous tubes, which had probably invested the 

 delicate filaments of the alga;. 



It a])peared important to determine the cause of the prcci])ita- 

 tiou of the organic matter from the water which had been in 

 ccuitaet with iron ; and in the hope of elucidating this interesting 

 question, the Directors of the Conqjaiiy recjuested me to pro- 

 ce(;d to Amsterdam to insi)ect their works. As anticipated, the 

 Duin canals were found to be choked up with atiuatic plants; 

 and at the sides, and wherever the current was sluggish, were 

 larg«! masses of dead alg;e floating on the surface. Tiic sand at 

 the bottom, originally very white and i)ure, was blackened to 

 some dc])th ijy decaying vegitaljlc matter, and when disturljcd, 

 numerous bubbhis of feti<l marsh -gas escaped. 



E2 



