62 



Discussion. 



The Peesident, in asking the Fellows to express their views 

 of the subject on which the paper had just been read, said 

 there could be no more important question than that of drain- 

 age. The w^orks at present being carried on in Adelaide were 

 very extensive, and it would be very disappointing if they were 

 not a success. He thought that the smells from the street- 

 gratings w^ere often very disagreeable, and he had noticed that 

 they w^ere w^orse in summer than in winter. He accounted for 

 this by the greater difference of temperature that existed in 

 the hot weather ; this would cause a suction action out of the 

 drain iii proportion as the street air became more rarified by 

 the heat. He thought the law of the diffusion of gases would 

 also exert a considerable influence. 



Hon. Allan Campbell remarked that by the plan carried 

 out in the formation of the deep drains in Adelaide there could 

 be no storage of sewage anywhere in the system, and conse- 

 quently no sewer gas could be formed. He thought that there 

 was a good deal of misapprehension on the part of the public 

 as to the nature of sewer gas and of sewer air. The former 

 could only result from decomposing sewage ; the latter was 

 simply stagnant or foul air, such as would be noticed in any 

 space that had been shut up for any length of time. In the 

 system of deep drainage they were now considering the only 

 outlet for the sewer air was at the street gratings. The chief 

 factor in causing motion or a current in air was, in his opinion, 

 variations of temperature. He thought that there was a 

 greater stagnation in the air of the drains in summer than in 

 winter owing to the temperature of the outside air being then 

 higher, and therefore lighter, than the sewer air, and hence 

 there would be no tendency for the formation of a current of 

 air into the sewer through the street grating. In winter, on 

 the contrary, the street air being colder, and therefore heavier 

 than the sewer air, there would be a greater tendency for air to 

 ejiter the drain. The first important point in any system of 

 drainage was to isolate the interior of the houses from any 

 chance of becoming contaminated by the sewer air. He thought 

 that the plan adopted by the South Australian Government 

 was a very effectual method of trapping, and ought to secure 

 the end desired. The second great desideratum was to have a 

 free outlet for the escape of the sewer air at some elevation. 

 This alone would not always ensure a proper ventilation of 

 the drain ; and to effect this it might be necessary to place 

 cowls on the ventilating pipes to overcome the stagnation. 

 The tendency to stagnation would not always be equally great, 

 as, for instance, in winter. In reply to an opinion that a high 



