306 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



of chemical evidence in the case of sewage or sewage effluents, 

 the factors generally determined in a sewage analysis are : — 



(a) Total oxidisahle matter as measured by the oxygen 

 absorbed from acid permanganate in four hours and in three 

 minutes ; 



(6) Nitrogen, either ammoniacal, albuminoid, nitrous or 

 nitric ; 



(c) Chlorine ; 



(d) Suspended matter ; 



(e) Putrescibility ; 



if) Consumption of dissolved oxygen. 



The objects of sewage analysis may be defined as follows : — 



(1) To determine the character of the sewage to be treated. 



(2) To determine the efficiency of purification works. 



(3) To determine the effect of the discharge of sewage or 



effiuents into various bodies of water, either river, 

 lake or sea. 



1. Taking these objects in order, it is of great importance, 

 when designing works for sewage purification, to ascertain the 

 concentration or strength of the sewage to be treated, as the 

 amount of filter space provided must necessarily depend on 

 the amount of organic matter to be transformed. 



The Local Government Board has recently issued a memo- 

 randum, based on the Fifth Eeport of the Eoyal Commission 

 on Sewage Disposal, which defines roughly what is meant by 

 ' strong,' ' average,' or ' weak ' sewage. Using permanganate, 

 1 c.c. of which equals one milligram of oxygen (which is ten 

 times the strength frequently used), and assuming that the 

 determination is made at 80° F., the amount of oxygen 

 absorbed by the different strengths of sewage is taken as 

 follows : — 



' Strong ' sewage 17 to 25 parts per 100,000 



' Average ' sewage 10 to 12 parts per 100,000 



' Weak ' sewage 7 to 8 parts per 100,000 



