14 



WATER 



such waters contain harmful organisms or acquire offensive odors or tastes 

 that they become objectionable. A good drinking water should be clear, 

 colorless, odorless, have a cool and refreshing taste, and be free from harm- 

 ful organisms. 



In the chemical examination of water the different forms of nitrogen 

 are regarded as the best index of the quality of the water. The water 

 is analyzed for its content of albuminoid ammonia, ammonia, nitrites, 

 and nitrates. These different forms of nitrogen are closely related to one 

 another. The albuminoid ammonia really represents protein nitrogen and 

 is readily converted by organisms into ammonia. Other organisms then 

 oxidize the ammonia to nitrites and nitrates. The nitrogen of the nitrates 

 may then be utilized by plants that grow in the water and be again built 

 up into proteins. These processes are called ammonification and nitri- 

 fication and form a part of what is known as the nitrogen cycle in nature. 

 The relation of the different forms of nitrogen may be expressed by the 

 following equations in which glycine is taken to represent protein: 



Ammonification: 



2CH0NH0COOH + 3O2 = 2NH3 + 4CO2 + 2H2O 

 Nitrification : 



2NH3 + 30o = 2HNO2 + 2HoO 

 2HNO0 + O. = 2HNO3 

 2HNO3 + CaC03 = Ca(N03)o + HoO + COo 



These compounds of nitrogen are not toxic in the quantities in which 

 they occur in water. Far more ammonia, for example, is produced as a 

 result of metabolism than is consumed in the drinking of water. How- 

 ever, the presence of a constant and continuing supply of albuminoid 

 ammonia, ammonia, and nitrates may indicate that the water is being 

 contaminated by sewage, since these forms of nitrogen are particularly 

 high in sewage. A state of change is regarded as a state of danger and 

 calls for careful investigation as to the origin of these forms of nitrogen. 

 Care must be observed in interpreting the data obtained by analyzing 

 water. The normal nitrogen content of such waters must be known be- 

 fore judgment can be passed. Deep well water would not have the same 

 nitrogen content as a surface or spring water. It is necessary to know 

 something of the topographical features surrounding the water supply. 



The chloride content of water is often also of value in determining the 

 character of the water. If it has been polluted by sewage, the chloride 

 content will be abnormally high. Here again, however, it is necessary 

 to observe great caution in passing judgment. Waters from along the 

 coast or from regions where salt deposits exist may be very high in 

 chlorides and still be perfectly safe. It is not the absolute amount, but 



