318 



Water and its Impurities, with 



The order of growth and decay of the organisms whose 

 death makes the offensive gases, depends upon the relations 

 of animal and vegetable life in the water. First usually 

 there is in stagnant places, the confervoid growth already 

 described which increases with great rapidity and is found 

 largely at the lower part of Rensselaer lake where it is 

 carried by the slight drift of the water towards the con- 

 duit. It passes through this into the reservoir (see p. 314), 

 and when carried into the pipes supplying the city, dies ; 

 this is probably due to the effect of the iron 1 and as it occurs 

 out of the reach of the atmosphere, aeration is prevented, 

 and the gases resulting from decay are drawn with the 

 water at the hydrants : when these gases are in the water 

 animalcula are again found and the smell of sulphuretted 

 and phosphuretted hydrogen appears. This order of 

 change may be varied by several influences. When the 

 plaut is in full growth in the lake, there is a varying amount 

 of it dying from natural causes, and the conditions produced 

 by its decay are unfavorable to the remaining crop which 

 dies rapidly, until the whole mass, buoyed up by adherent 



1 It has been supposed that the plant is killed by the pressure to which 

 it is subjected in these last pipes ; this cannot be so for the smell which is 

 the indication of its death, was as offensive, or more so, on the hill where 

 there was not enough pressure to draw it all the time, as it was in any 

 part of the city. 



During the discussion, the question arose as to whether all of the plant 

 was killed by the time it was drawn, and it was stated by Prof. Howard 

 Townsend that he had found the plant in microscopic examinations of 

 water which had been drawn from his hydrant in town. This fact is fatal 

 to the theory that the plant is killed by pressure, if the fact already stated 

 is not so; if it were, all would be killed, since all portions are subjected 

 to a pressure that is uniform; if, however, it results from the action of iron, 

 many of the confervoid stems might not meet with sufficient contact 

 during their short passage to cause their destruction. 



During the ensuing summer, after reading this paper, the proof of this 

 effect of iron upon this organic matter in the water of Rensselaer lake 

 was experimentally shown to the members of the Institute at one of its 

 meetings. 



