IOWA ACADEMY OF SCIENCES. 



77 



point of view and by many it has been called a digestion 

 process. The organic matter in the sewage after it has 

 remained in the tank for some time, undergoes a change 

 which prepares it so that it can be oxidized much more 

 readily in the nitrification process. As an illustration to show 

 the changes which the sewage has undergone, the results of 

 the determination of free ammonia may be taken. The 

 results taken are for the cubic centimeters of the standard 

 ammonia as determined by each tube. 



It will be noticed that after the distillation of 18 tubes 

 in the manhole sample the free ammonia showed no signs 

 of decreasing or is there any period in the analysis where 

 the distillation of the free ammonia may be said to be 

 complete. In the tank sample ten tubes were only 

 required for the complete distillation of free ammonia 

 while the effluent was complete with five tubes. Another 

 interesting change which takes place as the result of the 

 decomposition in the septic tank is in the determination 

 of solids. In the solids at 180^^ C. it is noticed that the 

 residue in the manhole sample is quite black and shows 

 very strongly that organic matter is present. The sample 

 from the tank in contrast gives very readily a grayish or 

 nearly white residue. The chemical changes which take 

 place in the septic tank are very complicated and offer a 

 field for special research. 



