SOME REMARKS ON SEWER AQE SYSTEMS. Ill 



near Berlin ; and, in a letter recently written by the Chair- 

 man of the Sewage Committee, does so without complaint 



and at a profit. 



Ventilation. 



One of the most vexed points of late years with regard 

 to all water-carriage systems is that of ventilation. 



1. Whether it is absolutely necessary. 



2. How it is to be accomplished. 



At present the pro-ventilationists undoubtedly hold the 

 field, though there are some notable and successful excep- 

 tions, such as Bristol, to the general rule. Mr. B. Latham 

 an authority on sewerage, lays it down that all sewers 

 must be ventilated by free communication with the out- 

 side air. This rule has been generally followed ; but 

 — partly on account of the fault previously mentioned, of 

 sewers so fiat that they are sewers of deposit, and partly, 

 no doubt, through bad workmanship, which causes accu- 

 mulation of decomposing matter — these ventilators have 

 been a continual bugbear to the public and a thorn in the 

 flesh to the engineer. 



That a systematic ventilation of sewers, by means of 

 shafts communicating freely with the open air, is not abso- 

 lutely a necessity, is proved by their non-use in Bristol, and 

 the city's excessively low death-rate. 



It is not of course likely that the Bristol sewers are 

 absolutely without any air currents • but the internal and 

 external air have not designedly any free communication. 



In providing ventilators, the necessity for the presence of 

 gas in sewers is taken for granted ; but sewer gas being the 

 product of decomposing matter, it follows that the more 

 quickly such decomposing matter is taken away, the less 

 will sewer gas be formed. Ventilation is therefore clearly 

 dependent on the construction of the sewer. A sewer badly 



