194 
the latter. The small amount in Quiver Lake is attributable 
to its greater independence of the river, to the paucity of its 
plankton, and to the sandy nature of its drainage basin and 
consequent share of spring water in its water supply. It is 
noticeable that the large amount of submerged vegetation in 
this lake does not contribute any great amount of organic 
nitrogen to the water at any season of the year. 
The nitrogen as albuminoid ammonia is included in the to- 
tal organic nitrogen, and exhibits almost identical relative 
amounts in the four localities, though actual quantities are 
only half as great. It represents the nitrogenous materials 
which have not undergone decomposition. 
The nitrogen as “ free” ammonia represents the ammonia 
contained in the water in free or saline condition. Itis a prod- 
uct of the decomposition of organic matter in the first stages 
of oxidation, and its quantity is an indication of the amount 
of such matter present in the water in a partially decomposed 
state. It is abundant where sewage occurs, and together with 
the chlorine affords evidence of the degree of contamination, 
The occurrences of free ammonia in the four localities (.86, 
.245, .165, and .422) are not in most instances in the same ra- 
tios as those of the chlorine (21.6, 3.8, 4.8, and 16.3) or of the 
plankton (1.91, .884, 1.62, and 6.68). The excess (two to five 
times as much) of decaying organic matter in the river as com- 
pared with the other situations is apparent, and is doubtless due 
to the concentration of sewage in its channel and to the more 
recent access of the sewage there as compared with that in the 
reservoir backwaters, as, for example, in Thompson’s Lake. 
The early stages of decay are in consequence more active in 
the river. The free ammonia is high in both the river (.86) and 
Thompson’s Lake (.422) but lower in Spoon River (.245), where 
the organic material in suspension is considerable, as indicated 
by the loss on ignition, the albuminoid ammonia,and the organic 
nitrogen and oxygen consumed. The decay of this matter and 
the accompanying release of free ammonia has not been attained 
as yet in a part at least of the silt in Spoon River to the same 
