IOWA ACADEMY OF SCIENCES. 



79 



In addition to the above the following analyses of Mt. 

 Pleasant and Grinnell sewage will serve to show the com- 

 position of sewage from the smaller cities of the state. 



MT. PLEASANT. GRINNBLL. 



Chlorine 165. 96. 



Solids on evaporation, 5402. 1010. 



Solids at 180° C 5332. 906. 



Solids on ignition 1450. 664. 



Albuminoid ammonia 31.5 10.0 



Free ammonia 53 . 5 13.6 



Nitrites 0.0 0.8 



Nitrates 00 4.0 



Oxygen consumed, 3 minutes 32.6 1.18 



Oxygen consumed, 15 minutes 31.62 8.4 



Oxygen consumed (4 hours) 45.46 10.30 



Oxygen consumed, Asso. meth 94.40 20.7 



The water used by the college is furnished from a well 

 2,215 feet deep and a recent sanitary analyses gave the 

 following results: 



PARTS PER MILLION. 



Free ammonia .18 



Albuminoid ammonia .024 



Chlorine 51 . 



Solids on evaporation 1226. 



Solids at 180° C 1180. 



Solids on ignition 1040. 



Nitrogen as nitrites .4 



Nitrogen as nitrates T . 



Oxygen consumed, 15 minutes .32 



Oxygen consumed, 4 hours .48 



The large amount of solids and of chlorine increases the 

 amount of these substances in the results obtained from the 

 sewage and should be considered when comparisons are 

 made with the sewage from other localities. 



The chemical composition of the sewage is of great im- 

 portance, but the test of its purification is the composition 

 of the effluent. Some effort has been made to establish 

 standards for the effluents, and the limit allowed by the 

 Mersey and Irwell Joint Committee is that the effluent 

 shall not absorb over one grain of oxj^gen per gallon in 

 four hours (one grain per imp. gallon equals 14,3 parts per 

 million). The same committee limits the albuminoid 

 ammonia in the effluent to .1 grain per gallon, or 1.43 parts 



