Till-: LOCAL WATKR SUPl'LY. 9 



The significance of the results olHained l)y chemical ana- 

 lysis may be briefly stated as follows : 



The Albuminoid Ammonia is a measure of the amount of 

 undeconiposed nitrogenous organic matter in the water, this 

 ammonia being produced from the organic matter by artificial 

 decomposition in the lal)oratory. 



The Free Ammonifi indicates the presence in the water of 

 nitrogenous organic matter in the actual process of decompo- 

 sition, the ammonia being- the natural product of such decom- 

 position. 



Nitrogen as Nitrites shows the presence of nitrogenous 

 organic matter but recently decomposed, being the first step in 

 the oxidation of the ammonia. 



Nitrogen as Nitrates shows that the nitrogenous organic 

 matter is still further removed in point of time ; in other words, 

 that it is completely oxidized and inert. 



Chlorine as Chlorides indicates, as a rule, direct sewage or 

 barnyard contamination. Since all soils, however, contain a 

 certain amount of natural chlorides, allowance must be made 

 for these in considering this item. 



Required Oxygen, or Oxygen Consuming Capacity-, gives 

 tlie amount of oxygen necessary to oxidize the organic matter 

 in the water, including both animal and vegetable impurities. 



By Total Solids is meant the residue remaining on evapo- 

 ration to diyness. If this residue is ignited and then reweighed, 

 the difference gives the amount of organic matter present — 

 plus, however, some of the chlorides, which are driven off by 

 the heat. 



It is evident that the above chemical impurities, in the 

 amounts ordinarily found, have absolutely no harmful effect of 

 themselves. They are simply the indices of existing or pre- 

 vious organic pollution. The figures do not in any way enable 

 us to ascertain the amount of organic matter that actuallj' 

 existed in the water, because of the complex and variable 

 composition of this matter. The best that can be done is to 

 measure the decomposition products of such impurity, and 



