Januabt 12, 1906.] 



SCIENCE. 



61 



cates the amount of nitrogenous matter 

 that has undergone complete decomposi- 

 tion. It is rarely absent from a normal 

 water. It is never present in any large 

 amount, seldom exceeding one tenth of a 

 milligram per liter. Higher amounts than 

 this, being unusual, must be looked upon 

 with suspicion. 



The interpretations I have just made 

 apply chiefly to reservoir, pond and lake 

 waters. River waters differ from pond, 

 lake or reservoir waters in the essential 

 particular that the former are in rapid 

 motion and the so-called nitrogen cycle may 

 take place many times during the course 

 of their flow. High nitrogen as free 

 ammonia, as albuminoid ammonia and as 

 nitrites, characteristic of recent pollution 

 in ponds and reservoirs, may, in rivers, 

 be due to the decomposition of the algse 

 life, which was stimulated by the entrance 

 of sewage in the upper stretches of the 

 river, and the proper deductions to be 

 drawn from these nitrogen data necessitate 

 a knowledge of the river. 



Though much valuable information can 

 be obtained, as I have tried to show, from 

 the careful study of the nitrogen content 

 of a water, the water analyst does not de- 

 pend alone upon these factors in forming 

 an opinion as to the source of the organic 

 matter, and turns to other chemical as well 

 as to bacterial data to substantiate or 

 modify the opinion thus formed. From 

 the chemical point of view the most impor- 

 tant of these data is the combined chlorine 

 that a water contains. This is due to the 

 fact that though chloride of sodium occurs 

 in rain water, especially near the sea, and 

 in small amounts is found in all soils, it is 

 a characteristic constituent of sewage, the 

 animal body expelling the same amount of 

 salt as it absorbs. 



A careful study of the amount of com- 

 bined chlorine in normal waters made 

 by Professor Thomas M. Drown, showed 



that in Massachusetts, where salt-bearing 

 strata do not occur, the amount of chlorine 

 in a surface water depended on its distance 

 from the sea, and that for Massachusetts 

 it was possible to establish normal chlorine, 

 or, as they are commonly called, iso chlor 

 lines. 



The work begun by Professor Drown has 

 been carried on by other investigators, and 

 to-day the iso chlor lines for all the New 

 England States and New York and New 

 Jersey have been determined. The result 

 of this work is that the amount of chlorine 

 occurring in the surface waters of the 

 above-named states gives most valuable in- 

 formation. Chlorine above the normal of 

 the region shows pollution. It does not 

 indicate whether the pollution is direct or 

 indirect, but does show that sewage, from 

 which the organic matter and the germs of 

 disease may or may not have been removed 

 by filtration through soil, has had access 

 to the water. Chlorine above the normal 

 is, therefore, always a suspicious sign 

 which must be investigated. I know that 

 it is claimed that in many of the western 

 states, owing to geological conditions, very 

 little information can be obtained from the 

 determination of chlorine. I believe, how- 

 ever, more careful and thorough work is 

 necessary to prove that such is the case, 

 and that further investigation may show 

 that though it is impossible to construct 

 iso chlor lines running through the state, 

 the normal chlorine of different localities 

 in a state can often be determined. 



Another factor that is often used in the 

 attempt to decide whether or not a water 

 contains an excessive amount of organic 

 matter is the oxygen consumed. The 

 oxygen consumed is not, however, a meas- 

 ure of the organic matter in a water, but 

 only a measure of the amount of mineral 

 reducing salts plus a certain amount of the 

 organic matter, the amount depending on 

 the method of determination used. It 



