r,s. 
VENTILATION-OF SEWERS AND DRAINS. 155. 
draught of 250 feet the air exhausted was 3,387 cubic feet per 
hour. 
Shafts without a cowl registered 1,883 cubic feet per hour, that. 
is a difference of 1,504 cubic feet in favour of the cowl or 79%. 
In another case the work with a cowl exceeded the open pipe by 
3,688 cubic feet per hour, or an increase of 76°7/. These cowls. 
were by different makers, and each was tried simultancously with 
the open pipe. 
The work of the first and second class cowls considerably exceed 
the foregoing tests. As inspection boxes were not fixed on the 
first installation, a length of sewer was selected to test the aerating 
effect of the shafts. The distance between the induct and exhaust 
shaft was 990 feet. Anemometers were placed in each shaft so 
that the whole of the air passing into or out of the sewer would 
be registered. 
No. 1 Return from Ist March to 28th June shewed that the air 
was changed on an average 2:35 times in the hour or every 25°35 
minutes. Average wind velocity nine miles per hour. On one 
occasion the air was not changed more than once in two hours, 
and the test papers shewed that hydrogen sulphide was present 
sufficient to discolour the paper. No.2 Return from 10th July to: 
2nd October 1890 the air was changed on an average 2°39 times 
in the hour or every twenty-five minutes, average wind velocity 
8°93 miles per hour. 
In a test made at an intermediate point, viz. 200 feet from the 
induct shaft, the anemometers shewed that at this point the 
aerating effect was equal to 217 of the wind force, whereas in the 
long length it did not exceed 13:87, showing a loss of 7:27 due 
to friction and other causes. The length of the sewer was jointed 
with cement, but there were several houses connected without a 
boundary trap which would no doubt interfere with the air currents, 
all yard sinks were properly trapped. 
The results of the trial referred to by Mr. Strachan at Chelsea 
are summarized as follows :— 
