TECHNICAL AND SANITARY PROBLEMS 1073 



intensifies an odor. In water analysis it is common to report the 

 odor of both hot and cold water. 



Cause of Odors. The odors are caused by aromatic oils that are 

 produced during the growth of the microscopic organisms. After 

 disintegration the oily substances are scattered through the water. 

 In many instances the oils are characteristic of the organisms and 

 the presence of organisms in water can sometimes be determined 

 merely by the odor. They cannot always be thus recognized, 

 however, for the quality of an odor changes with its intensity. Cer- 

 tain organisms present in small numbers impart to the water an 

 odor that might be termed aromatic, but when the same organisms 

 are present in larger numbers the odor might be more properly de- 

 scribed as fishy. The amount of oily matter required to produce a 

 noticeable odor is very small. The oily substance that gives 

 Synura its odor is recognizable when diluted to the extent of one 

 part in twenty-five million parts of water. This is not surpris- 

 ing, however, as the oil of peppermint can be recognized in a 

 dilution of one part in fifty million parts of water. The odors 

 of organisms are intensified by heating, by mechanical agitation, 

 by a change in the density of the water, by pressure, and by any 

 other cause that tends to rupture the cell walls and liberate the oil 

 globules. 



The following table gives the natural odor of a number of the 

 common microscopic organisms. For convenience they may be 

 grouped around three general terms, aromatic, grassy, and fishy. 

 The aromatic odors are due chiefly to diatoms, one of the strongest 

 being that produced by Asterionella. Some of the green algae 

 produce sweetish, grassy odors, and this is even more true of the 

 blue-green algae. Anabaena produce an odor that varies greatly 

 according to its dilution, and various epithets have been applied to 

 it. The fishy odors are the most disagreeable of any observed in 

 drinking water, and that produced by Uroglena is perhaps the worst. 

 The water that contains this organism in large numbers may have 

 an odor resembling that of cod liver oil. The odor of Synura is 

 almost as bad and even more common. When organisms decay 

 moldy or musty odors may be produced. But these odors of de- 

 composition are less characteristic than the odors of growth. Some 



