60 



SCIENCE. 



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



certain waters known to be polluted, and 

 the same can also be said of nitrogen as 

 free ammonia and the nitrogen as nitrites 

 and nitrates, and yet something can be 

 learned from the consideration of each of 

 these factors. Nitrogen as albuminoid am- 

 monia in a water analysis, as has been said, 

 represents the nitrogenous matter which 

 has not undergone decomposition, and it is 

 found that in unpolluted waters this 

 amount varies greatly, some waters giving 

 almost no nitrogen in the above form, 

 others as much as one milligram per liter, 

 if, however, the nitrogenous substances are 

 of vegetable origin the water is usually 

 highly colored, and consequently a colorless 

 water, containing that amount of nitrog- 

 enous matter represented by 0.25 milligram 

 of nitrogen as albuminoid ammonia per 

 liter is looked upon with suspicion.^ 



Free ammonia always indicates organic 



^It has lately been suggested that the deter- 

 minations of organic nitrogen should be substi- 

 tuted for the determinations of nitrogen as 

 albuminoid ammonia in water analyses. There 

 is, of course, no question that nitrogen as albumin- 

 oid ammonia only gives the amount of nitrogen 

 that is present in nitrogenous substances decom- 

 posed by an acid solution of potassium perman- 

 ganate, and not the total organic nitrogen. With 

 waters, however, unless greatly polluted, the 

 amount thus obtained equals approximately one 

 half of the organic nitrogen, so that the organic 

 nitrogen, if desired, can be calculated sufficiently 

 closely from the nitrogen of the albuminoid am- 

 monia. In sewage work, however, the case is 

 very different. There is no fixed ratio between the 

 organic nitrogen and nitrogen as albuminoid 

 ammonia, and in determining the strength of a 

 sewage, and in determining the amount of purifi- 

 cation that takes place in various processes of 

 treatment, the organic nitrogen is a most im- 

 portant factor and should be determined. The 

 nitrogen as albuminoid ammonia, on the other 

 hand, is of little value, changing as the sewage 

 ages, "on account of nitrogenous substances not 

 acted upon by an acid solution of potassium per- 

 manganate breaking down, giving nitrogen com- 

 pounds more easily decomposed. The amount of 

 nitrogen as albuminoid ammonia, as a rule, 

 increases as the sewage ages. 



matter in the process of decomposition. 

 In unpolluted surface waters it is rarely 

 high, being removed almost as fast as 

 formed by vegetable and animal organisms 

 in the water and an amount of nitrogen as 

 free ammonia above 0.05 milligram per 

 liter is unusual, and if it does occur the 

 water can not be considered as an unpol- 

 luted water unless that fact is clearly es- 

 tablished by other data. 



In drawing conclusions, not only from 

 the nitrogen as free ammonia, but also from 

 the ratio that exists between the nitrogen 

 as free ammonia and the nitrogen as al- 

 buminoid ammonia, what is known as the 

 'seasonal variation' must be considered. 

 Namely, that the amount of nitrogen as 

 free ammonia in northern surface waters 

 is usually greater during the late autumn 

 and early winter than at any other time. 

 This is due to two facts: first, that in cold 

 weather the free ammonia is not absorbed 

 quickly by plant life, and second, that as 

 cold Weather begins the surface water of 

 ponds and reservoirs, growing colder, sinks 

 and the bottom water rises, bringing with 

 it the decaying matter from the bottom, 

 increasing the amount of free ammonia 

 often to three times the average amount of 

 the year. This also affects to a certain 

 extent the nitrates, but not nearly to the 

 same amount. 



The nitrogen in the other two nitrogen fac- 

 tors of the nitrogen content occurs only in 

 very small amounts. Nitrites in a water are 

 due either to the oxidation of ammonia or 

 to the reduction of nitrates, and being un- 

 stable quickly undergo change. Formerly, 

 nitrogen as nitrites in amounts exceeding 

 0.002 milligram per liter were thought to 

 be a strong indication of recent pollution, 

 and though we now know that unpolluted 

 swamp waters may contain over twice that 

 amount, still more than 0.002 milligram is 

 an unfavorable indication. 



Nitrogen in the form of nitrates indi- 



