THE VALUE OF PURE WATER 65 



people would object to it. It may be thought that this proportion is 

 too low, but it must be remembered that colored waters are invariably 

 accompanied by a vegetable odor and often by a slight turbidity, and 

 that it is the sum of the several quantities which determines the esthe- 

 tic rating. 



Experience has shown that objection to color varies directly with 

 its amount; consequently this curve has been plotted from the equa- 



tion, p c = - , i. e., a straight line, where p c stands for the per cent of 



objecting consumers, and c for the color. 



In the case of turbidity, however, small amounts count for more, 

 relatively, than larger amounts. The equation for the turbidity curve 

 has been taken, therefore, as p t = 5 V t, where / stands for the turbidity. 



With odor, however, the opposite condition prevails; faint odors 

 count for little, but distinct and decided odors cause much more com- 

 plaint. Consequently, the per cent of objecting consumers has been 

 made to vary as the square of the intensity of the odor expressed 

 according to the standard numerical scale. The quality of the odor 

 makes quite as much difference as its intensity, and for that reason 

 three curves have been plotted, one representing vegetable or pondy 

 odors (O v )j one representing odors due to decomposition (Oj), and 

 one representing the aromatic grassy and fishy odors due to micro- 

 scopic organisms (O ). These curves are plotted from the following 

 equations : 



in which O , O& and O v stand for the intensity of the three groups of 

 odors mentioned. 



These curves represent somewhat imperfectly our present ideas as 

 to the relative effects of color, turbidity, and odor; and on further 

 study they are likely to be considerably modified. 



It is a well-known fact that in cities which are supplied with water 

 which is not attractive for drinking purposes, large quantities of 

 spring water and distilled water are sold, and that consumers go to 

 much expense in the purchase of house filters in order to improve the 

 quality of the water furnished by the city mains. It is fair to assume 



