STERILIZATION 189 



oxygen consumed) from 2*5 to 4*4 parts per 100,000, and a 

 contact of from one to four hours (Experiments 12 to 59), the 

 coH and the enteritidis spores were absent from i c.c, and 

 ■in most cases from 5 c.c. The total organisms were very 

 [greatly reduced : they were not regularly counted, as of less 

 [importance, but on four occasions they have been lowered 

 [from the many millions originally present to 20, no, 140, 

 [and 600 per c.c. Even the last number is below that usual 

 in rivers. 



The anaerobic organisms were found to have been reduced 

 from an average of 2,500,000 per c.c. in the untreated septic 

 effluent ; to 200 after one and a half hours' contact with the 

 chlorine solution, and 150 per c.c. after three hours. 



Incubation tests, by mixing with 3 parts of the river water, 

 showed that the untreated effluents had a smell at first, which 

 progressively increased, while the dissolved oxygen rapidly 

 disappeared ; but the mixture with treated effluent kept sweet, 

 and the dissolved oxygen did not sensibly decrease in twenty- 

 four hours, and did not fall below 3 c.c. per litre in the closed 

 vessel for three or four days. 



A feature common to all oxidation treatments, the rapid dis- 

 appearance of the reagent at the first onset, suggested that 

 there might be an advantage in adding the solution in suc- 

 cessive portions. This modification takes a longer time, and is 

 apt to leave a residue of available chlorine, requiring a storage 

 of 8 to 18 hours for its disappearance. Where such storage is 

 possible it tends to a complete sterilization of the liquid. 



By estimating the dissolved oxygen in mixtures of 3 parts 

 river water to i of septic effluent, I proved that with 

 untreated effluents after 19 hours the oxygen had entirely 

 disappeared ; while with the treated, after an initial fall, it rose, 

 so that after 3 days it was higher than at first, and almost 

 equal to the river water. It remained throughout well above 

 the quantity essential to fish life. This proportion of effluent 

 is larger than in practice would be discharged into river waters. 

 The result may be due to the destruction of the putrefactive 

 bacteria by this treatment, leaving the oxidizing organisms pre- 

 dominant, so that the river does not foul. Two or three days, 

 the time of the incubation tests, brings the whole liquid down 

 to the sea. 



Primary, Secondary, and Tertiary Contact-Beds. — In a large 

 number of experiments I found that, as in the different stages 



