60 AGRICULTURAL CHEMISTRY 



with decaying animal and vegetable refuse matters, the 

 soluble parts of these materials along with the countless 

 organisms which they contain, become a part of the 

 drinking water. The impurities in well waters are ( i ) 

 organic matter, and (2) mineral salts. When waters are 

 charged with excessive amounts of organic matter, the 

 solids obtained by evaporating the water to dryness 

 blacken when ignited. The carbon compounds in a liter 

 of some water will require 20 mgs. or more of oxygen for 

 oxidation. The organic matter may decompose and be- 

 come harmless, but it is liable, in times of epidemics, to 

 furnish food for disease germs. 



A water that is comparatively free from organic matter 

 is not nearly so apt to be a source of trouble by conveying 

 disease germs as one that contains a large amount of 

 organic refuse, as this is the best kind of food for the 

 development of germs which cause many of the most fatal 

 diseases. Vegetable matter, as a rule, is not as harmful 

 in a water as is animal matter. The organic matter that is 

 dissolved in waters is constantly decaying ; this decom- 

 position is the result of the workings of minute organisms 

 known as bacteria, and the disease-producing bacteria may 

 be present as well as the harmless kinds. The history of 

 the water supply of large cities has shown that a water 

 which is comparatively free from organic matter is the 

 best for household purposes. The reasons are obvious. 

 Excessive amounts of nitrogenous organic matter in 

 drinking waters are particularly objectionable, as the 

 source of this material is often sewage or surface drain- 

 age, as from a swamp. 



