Free ammonia (that is, nitrogen as free ammonia) ranged from a low of 

 0.002 to a high of 0.033 part per million in the various samples. However, 

 the means for the stations agreed quite closely; they ranged from 0.009 to 

 0.015, with a mean of 0.013 for the whole area. Albuminoid ammonia ranged 

 from 0.100 to 0.260 in the samples, and from 0.1l5 to 0.182 in the station 

 means, with a mean of 0.l5l for the area. Thus, on the average, the amount 

 of albuminoid ammonia was about 12 times as great as the free ammonia. 



The most rare form of nitrogen was nitrite, which ranged from 0.000 to 

 O.OlU in the samples, and from 0.002 to 0.008 in the station means, with a 

 mean of 0.005 for the area. Nitrate was consistently more abundant than 

 nitrite, ranging from 0.02 to 0.2[i in the samples, and from 0.06 to 0.12 in 

 the station means, with a mean of 0.10 for the area. On the average, then, 

 nitrate was 20 times as concentrated as nitrite. 



Table 23 permits a comparison of the Island Section of Western Lake Erie 

 with several other waters with respect to the concentration of chloride and 

 compounds of nitrogen. It is not known when Mason (1917) took his samples. 

 Otherwise, with the exception of the data from V/hipple (1913), which were 

 taken in August only, the data in this table are based on samples taken in 

 the months of July, August, and September. The figures on Lake Erie at Cleve- 

 land and OP- Lake Michigan at Lake Forest are based on samples taken in two 

 successive years. In each case the figures represent means of several samples. 



The amount of chloride in the Island Section was decidedly higher than in 

 the pure waters reported by Mason, and higher even than in the polluted waters. 

 Concentration of chloride is regarded as a valuable index of the degree of con- 

 tamination by domestic sewage and certain tji^es of trade wastes, provided the 

 normal chloride content of the water is known. A lake may have a high chloride 

 content and yet not be polluted, for tributary streams may bring in water 

 which has come in contact with deposits of salt. Thus the high chloride of 

 the Island Section as compared with the pure and polluted waters reported by 

 Mason is not, in itself, evidence of pollution. The significance of the high 

 chloride content of Lake Erie will be taken up in later pages of this report, 

 following the presentation of data on the streams entering the lake at the 

 west end. It will suffice to say here that the chloride is derived from both 

 natural and pollutional sources of sodium chloride. That the amount of chlo- 

 ride present (10.3 parts per million) is far too small to be harmful to organ- 

 isms scarcely need be stated. 



The results of analyses for nitrogen given in Tables 21 and 22 probably 

 would lead a sanitary engineer to regard the water as unsuitable for domestic 

 consumption before treatment. The frequent presence of albuminoid ammonia in 

 excess of 0.l5 part per million, and the presence of considerable amounts of 

 nitrite would suggest oollution at once. The samples showing albuminoid am- 

 monia in excess of 0.20 oart per million would be open to suspicion particu- 

 larly. It is entirely possible that such values are normal to the lake, but 

 in view of the fact that the lake is subject to pollution by domestic sewage 

 from many sources, it is difficult to escape the conclusion that the nitrogen 



83 



