210 Scientific Proceedings, Royal Dublin Society. 
Confining our attention for the present to the results of the 
analyses of the fresh samples, one of the first points which will 
strike us is the decided quantity of free ammonia present in the 
unfiltered water, and the interesting fact that practically the whole 
of it becomes nitrified to nitric acid during the passage of the 
water through the filter-beds. This nitrification we may take 
in the light of recent research to be the result of the activities 
of the gelatinous layer of living matter gradually deposited on 
the surfaces of the material composing the upper portions of the 
filter-bed. 
Other evidence of the activity of the nitrifying organisms in 
the filter-bed, besides the oxidation of ammonia here shown, is 
afforded by the decrease in the quantity of dissolved atmospheric 
oxygen, and in the increase of the carbon dioxide, which the water 
suffers on passing through the filter-beds. The figures in the 
table giving the weights of these gases in the unfiltered and 
filtered waters respectively, show that a decrease of oxygen equal to 
-208 and an increase of carbon dioxide equal to 136 really occur 
during the passage of the water through the filter-beds. On. 
calculation, the quantity of oxygen required to oxidize the quantity 
of ammonia which is nitrified during filtration, viz. ‘031 parts, 
will be found to be equal to -117, while the weight of oxygen 
combined with -136 parts of carbon dioxide will be found equal to 
°099. The two quantities of oxygen, ‘117 and -099, together 
equal :216. This is somewhat in excess of the loss shown by the 
analyses, viz. ‘208, and allows nothing for other possible oxida- 
tions or absorption by the organism. I have invariably found, 
from a large number of experiments I have made on nitrification, 
that a loss of oxygen occurs over and above that required for the 
nitric acid and carbon dioxide which had been formed. The 
probable explanation of this not appearing in the analyses 
under discussion is, that it was quite possible for the water at 
the point where the sample was collected to have undergone 
slight oxygenation from the air after it had passed through the 
filter-beds. 
A. further point of interest in these analyses is the insight they 
give into the character of the organic matters, both in the unfil- 
tered and filtered waters. So far as the albuminoid-ammonia 
test can indicate, the quantity of organic matter in the filtered 
