The Air of Sewers. 







Carbonic 



Organic 



Micro- 







acid. 



matter. 



organisms.* 



Sewers 





1 



1 



1 







1-7 



13 



7x 



Houses < 





1*4 



0-45 



5x 





_four rooms and upwards . 



0-9 



0-3 





Schools < 





4*0 



1-6 



V7x 





_ mechanically ventilated . . 



2-3 



0-2 



2x 



On comparing the average amount of carbonic acid found by us in 

 sewer air with that found by earlier investigators (see above), it 

 appears that the sewers we examined must have been much better 

 ventilated than those previously examined. 



In our paper on the air of schools and houses, we pointed out 

 that in individual cases the amount of carbonic acid is not a measure 

 of the amount of the organic matter and number of micro-organisms 

 present in the air at the same time ; and that it is only when the 

 average of a comparatively large number of cases is taken that the 

 organic matter is seen to increase with the carbonic acid, while the 

 micro-organisms show no evident connexion with the carbonic acid 

 and organic matter. In the air of sewers the relation to one another 

 of carbonic acid and organic matter is similar. The micro-organisms 

 on the whole decrease as the other constituents increase. This is 

 shown in the following table, in which the organic matter and micro- 

 organisms are compared in amount with the carbonic acid as a 

 standard. The table is constructed by dividing all the carbonic acid 

 determinations into three equal groups according to the amounts of 

 carbonic acid found, and then taking the average of the corresponding 

 organic matter and micro-organism determinations in each group. 





Tempe- 



Carbonic 



Organic 



Micro- 





rature. 



acid. 



matter. 



organisms. 



Total 













55 '8° 



5-7 



51 



8-7 



6-7-7-9 „ „ 



53-1 



7'3 



6-3 



6-4 



8-6—10-9 „ 



53-0 



9-4 



10-5 



5-4 



* In this case we have represented the relation of the number for sewer air to> 

 that for air in four-roomed houses by x, as the calculated number for sewer air is 

 negative. The real value of x must be between f (= 1'3) and infinity. 



