or WATER FOR ORGANIC MATTER. 45 



When azotized compounds decompose and form am- 

 monia, how long is this ammonia retained in the water ? 

 On examining a very putrid stream, I estimated the amount 

 of ammonia at the most putrid portion, where carburetted 

 hj^drogen was passing off in great volumes, and where a 

 cubic foot could be obtained in a very few minutes by 

 stirring. 



In the sewage-stream of which I have spoken, the 

 amount of ammonia was from 0*5 to 0*7 grain per gallon. 

 After going 14 miles, the amount was only 0*07, and after 

 20 miles none at all was found. 



The mud of the same stream was in a state of putrefac- 

 tion, and contained, per cent : — 



Ammonia 0'797 



J, a mile lower 0*420 



at second mile o* 1 7 1 



The ammonia rapidly disappeared, and the mud itself 

 diminished very greatly in amount. 



I estimated that one grain of ammonia evaporated in 

 some seasons from every square foot per hour. 



In taking sewage-water to the land, I think it very im- 

 portant that the movement should be as rapid as possible. 



The water in its passage of 20 miles has lost its valuable 

 ammonia, and that within two or three days. This is a 

 sufficient proof that we must not trust to the ammonia as 

 an indication of the amount of the organic matter which 

 has been, as it is as rapidly removed as the organic matter 

 is decomposed; that is to say, the length of time 

 necessary for complete putrefaction is, under favourable 

 circumstances, no greater than the time afterwards re- 

 quired for the removal of its products. In this water 

 there was no life to be observed ; but the estimation of the 

 organic matter would have shown no difference, whether 

 vitality had been present and the substance had been 



