510 



Messrs. Carnelley and Haldane. 





Tempe- 



Carbonic 



Organic 



Micro- 





rature. 



acid. 



matter. 



organisms. 



In excess of outside air at same time : — 











0*4 — 2*5 vols, carbonic acid 



7-0° 



1-76 



2 2 



- 6-0 



2-8-4-4 „ „ 



55 



3-6 



6-3 



- 2'9* 



4-7-7-9 „ „ 



45 



6-0 



6-8 



-18-2 



Sources of the several Impurities in Sewer Air. 



The source of organic matter present in sewer air over and above 

 that present in outside air at the time is of course the sewage 

 itself. The organic matter arising from the sewage is most pro- 

 bably wholly or for the most part gaseous, for the conditions which 

 cause the number of micro-organisms in sewer air to be less than 

 in outside air would also affect any solid organic matter or dust in 

 a similar manner, so that we should expect the solid organic matter 

 in sewer air to be less than in outside air at the same time. The 

 gaseous organic matter arising from the sewage itself will pro- 

 bably be of two kinds, that volatile per se, and that volatile with the 

 aqueous vapour from the sewage water. Organic matter may also get 

 into the air in cases where splashing occurs from the entry of a side 

 drain high up in the wall of a sewer. 



The carbonic acid in sewer air over and above that in outside 

 air may have two sources. It may be due to diffusion into the 

 sewer from the neighbouring soil ; but probably its chief source is 

 oxidation of organic matter in the sewage and the air of the sewer. 

 Miller many years ago demonstrated the existence of such oxidation 

 in the Thames, when it was the recipient of all the London sewage. 

 He showed by a series of analyses of the gases dissolved in 

 Thames water, collected at various points above and below London, 

 that from Kingston to Greenwich the carbonic acid increased, while 

 the oxygen rapidly diminished. 



Two possibilities occur as to the source of the majority of the 

 micro-organisms in sewer air. They may in the first place be de- 

 rived from the sewage and sewer walls. If this were so to any 

 great extent we should expect their numbers to increase with the 



* The irregularity here is due to the results in the Dock Street sewer, which was 

 examined on a dry and windy day, when the micro-organisms in the outside air 

 were very numerous, owing to dust, so that the difference between outside air and 

 sewer air was very great (see the large table of results, p. 506). In the first 

 classification one of the Dock Street analyses falls into each class, in the second 

 classification two fall into the third class, leaving none in the second class. If the 

 Dock Street analyses were left out, or if the third class began at 4"9 vols, of carbonic 

 acid instead of at 4*7, the decrease in micro-organisms would run quite regularly. 



