The Relations between Marine Animai and Vegetable Life. 



379 



the rate of a litre in lOmÌDutes, only .075 mgm. free, and .125 mgm. 

 organic ammonia, or respectively 54^ and ?>1% less. In anotber 

 instance the water was drawn from the tap at varving- rates, in order 

 to determine the effect of the rapidity of flow on the amount of 

 ammonia removed. The following results were obtained. 



Here we see that when the water was allowed to run at its 

 maximum rate from the tap, 26^ of the free, and 25^ of the organic 

 ammonia was removed. When however the water was allowed to 

 drip slowly from the tap, no less than 82^ of the free ammonia 

 was in one case removed. The rate of flow in these cases was really 

 much faster than that given, as from the same pipe another stream 

 of water was rimning at the rate of a litre in 36 seconds. The exit 

 tube of this jet was situated about 16metres from the reservoir, hence 

 the water analysed only flowed at the very slow rate given above 

 through a length of four metres of pipe. The total internai area of 

 the whole pipe was calculated to be roughly about one and a third 

 Square metres, and hence it follows that exposure of a litre of water 

 to this area of the bacterial slime which coats the inside of the pipes, 

 was able, in ten seconds, to remove a quarter of the free and organic 

 ammonia present. This seems an extremely rapid rate of purification, 

 yet it should be remembered that in the previously described ex- 

 periments with sand kept in darkness, it was found that water could 

 be filtered at the rate of a litre in ten minutes, and yet bave ^1 % 

 of the free, and 20^ of the organic ammonia removed. 



In stili another determination, water running from the tap at 

 the rate of a litre in 47 minutes, was found to contain 30 X le^s free, 

 and "0% less organic ammonia than the water flowing at a litre in 

 12 seconds. 



As the bacterial slirae which covers the pipes is so efifectual a 

 purifying agent, it was thought that the brown vegetable matter 

 which is deposited from the water ou standing in the reservoirs 



