80 IOWA ACADEMY OF SCIENCES. 



per million. From an examination of the results it will 

 readily be seen that the college effluent meets these require- 

 ments with a few exceptions. The exceptions where the 

 albuminoid ammonia is especially high results from the 

 extra work required from the beds when the amount of 

 sewage is increased by storm water. When comparing 

 the results of the oxygen absorption, attention may be 

 called to the fact that previous to April 17, 1900, the 

 temperature at which the determinations were made 

 was 80^ C. and after that date 80^ F. as recommended 

 by the Society of Public Analysts of England. The 

 results made since April 17, 1900, are directly compar- 

 able with the results of the English investigations and it 

 will be seen that the results readily meet the limit of the 

 Mersey and Irwell Joint Committee. Since June 28, 1901, 

 the determinations made of oxygen absorption have been 

 the 3 minute test, the 15 minute test, the 4 hour test and the 

 Association test. The object of the first three tests may 

 be explained by the following statement of Mr. Frank 

 Scudder before the Society of Chemical Industry. 



The object of using these various time tests is to differentiate the qual- 

 ity of the organic matter and in order to make the point clear, he (Mr. 

 Scudder) divided the quality of the organic matter in the Safford effluents 

 into three divisions as follows : 



I. The three minute test showed the putrid matter decomposing per- 

 manganate at once with acid. Angus Smith said that this test measured the 

 organic matter decomposed or putrid or at least certain gases which it left 

 behind capable of decomposing permanganate. 



II. The fifteen minute test, that is fifteen minutes less the three minute 

 test equals a twelve minute test, showed ma ter readily putrefying and rap- 

 dly decomposing permanganate with acid. Angus Smith classed this as 

 organic matter readily decomposed and probably ready to become putrid. 



in. The four hour test minus the 15 minutes and minus the 3 minute 

 test which equals a 225 minute test for the action of the permanganate, 

 showed matter capable of putrefying, although slow to decompose. 



It is a matter of interest in connection with the three minute test that in 

 addition to the organic matter decomposed, nitrites and ferrous iron or 

 hydrogen sulphide if present react upon the permanganate. 



The explanation of the object of the time tests shows 

 that the results indicate to a certain extent the condition 

 of a part of the organic matter present in the sewage, but 

 these tests do not indicate the action on the entire quan- 



