522 



The Air of Sewers. 



Fergus found that free ammonia came through a somewhat similar 

 trap in 15 minutes, carbonic acid in 1-J hour, sulphuretted hydrogen 

 in 3 to 4 hours, &c. He also refers to similar experiments in which 

 a ventilating pipe was placed between the substance experimented on 

 and the trap, in which the result was much the same, except that the 

 time occupied in penetrating the trap was longer. 



Though it is thus the case that water-traps after some time allow a 

 certain amount of various volatile substances to pass through, yet it is 

 hardly conceivable that the small amount thus allowed to pass can 

 have any appreciable influence on health. 



We do not propose to enter here on any general discussion of the 

 effects of the inhalation of sewer air on health. The results of the 

 foregoing investigations are clearly such as to make us much more 

 suspicious as to supposed evidence of the bad effects of ordinary sewer 

 air, such as that of the sewers examined by us. At any rate it is 

 evident that " sewer ga,s," unless it has been vitiated by splashing, 

 has a much less deadly composition than is often supposed. It must 

 be remembered, however, that the matter cannot in the present state 

 of our knowledge be settled by analyses alone, though analyses may 

 serve as a guide in the investigation. 



