64 



SCIENCE. 



[N. S. Vol. XXIII. No. 576. 



from color, odor and turbidity, that the 

 amount of nitrogen as free and albuminoid 

 ammonia should be very much less than in 

 an unpolluted surface water, that the 

 amount of nitrogen as nitrates should not 

 exceed by more than 50 to 75 per cent, the 

 nitrogen of nitrates of normal waters, and 

 that the amount of chlorine should be the 

 chlorine of the region, and bacterially the 

 water should be very pure. 



To go further, and from the filtration 

 experiments and from the study that has 

 been made during the past twenty years on 

 ground waters, and express the statements 

 of the last sentence in concrete numbers, 

 it might be said that the best ground waters 

 should certainly contain not over 0.01 milli- 

 gram of nitrogen as free ammonia or over 

 0.02 milligram of nitrogen as albuminoid 

 ammonia, no nitrogen as nitrites, not over 

 0.1 milligram of nitrogen as nitrates in a 

 liter of water, and chlorine not above the 

 normal of the region. When a water con- 

 tains more than 0.05 milligram of nitrogen 

 as free ammonia and 0.08 milligram of 

 nitrogen as albuminoid ammonia, or 0.12 

 milligram of nitrogen as albuminoid am- 

 monia, even if the free ammonia occurs in 

 very small amounts, it is a sign of imper- 

 fect filtration or of subsequent pollution, 

 and consequently such water should not be 

 iised for household purposes. 



In making this statement, the fact that 

 the nitrogen of organic matter in a soil 

 can be oxidized by ferric oxide to ammonia 

 has not been lost sight of. This is, how- 

 ever, not of common occurrence, and unless 

 it can be proved in a given case to have 

 taken place, the deductions that have been 

 made must be considered as correct. 



Nitrites in a grovind water are a most un- 

 favorable indication, though they are some- 

 times found in unpolluted well waters, due 

 to the reduction of nitrates by iron, sand, 

 or iron pipes throTigh which the 'water is 

 drawn from the well. 



A ground water containing an amount of 

 chlorine much in excess of the normal of 

 the region and nitrogen as nitrates ap- 

 proaching 3 milligrams per liter, even with 

 very small amounts of nitrogen as free and 

 albuminoid ammonia, must be considered 

 to have been originally polluted surface 

 water, and on this account not a water free 

 from possible danger. 



Though, as has been stated, the num- 

 ber of bacteria in a ground water should 

 be small, not over one hundred per cubic 

 centimeter, numerous investigations of well 

 waters giving no indication of pollution 

 have shown that this number is often 

 largely exceeded. This may be and is often 

 due to the falling into a well of air and soil 

 bacteria. The number of bacteria in well 

 water, if not reaching into the thousands, 

 can not, therefore, of itself be considered 

 as an indication of pollution, though the 

 cause of excessive numbers requires ex- 

 planation. 



A much better indication as to the pollu- 

 tion of ground waters is the ratio that 

 exists between the number of bacteria de- 

 veloping at the temperature of 70° Fahr- 

 enheit and the number developing at blood 

 heat, and the same conclusions as with 

 surface water may be drawn from the ratio 

 that is thus found. 



The occurrence of acid forming bacteria 

 indicates pollution, and the presence of 

 colon bacillus in a ground water is almost 

 positive proof that sewage drainage is 

 present. 



Artesian or underground waters are 

 ground waters which have passed into or 

 through underlying rock strata. The sani- 

 tary value of the analyses of such waters 

 should be very great, for the pollution, if 

 polluted, may be due not only to careless- 

 ness, which allows direct and continuous 

 contamination from above, at the point 

 where the water is tapped, but often to 

 ground water which has not been purified 



