THE METROPOLITAN MAIN DRAINAGE WORKS. 
67 
i 
revolution they empty themselves of their contents into 
suitable receptacles provided for the purpose under the engine- 
house. What passes through the grating, then, into the 
absolute pumping-chamber is the finer and liquid sullage. This 
is pumped into the reservoir, where a further settlement of the 
lighter sediments still held in suspension will take place. If 
the sewage be allowed to go into the Thames, no deposit in the 
reservoir is wanted, and a very capacious flushing- culvert is pro- 
vided at its head to sluice out any settlements that take place 
during the period of rest while the sewage is pent up. If 
these sediments should have any commercial value they can be 
extracted by manual labour or by appropriate mechanical 
means; the reservoir being divided into four distinct com- 
partments, the entering sewage can be debarred by gates 
from each and any portion. The engine-house now erecting 
will contain four engines of 125-horse power each, and these 
can be applied collectively, separately, or in any combination 
that may be required ; the sewage which they will raise from 
the lowest arterial drain they will pump into an upper sewer 
above the level of the reservoir, into which it will flow through 
numerous smaller openings in the side of the upper sewer ; 
and after its periodic repose in the reservoir it will flow out 
again through other numerous outlets, forming a middle line of 
sewer between the two we have already mentioned. The 
following little sketch, not an actual section, but conveying 
the main principles and features, will render these arrange- 
ments more intelligible than words : — * 
Fig. 8. Plan of the Southern Outfall Pumping-Station and Reservoir at Crossness. 
* It is necessary to say, to disarm the criticism by engineers, that none 
of the illustrative diagrams to this paper are drawn to scale, or from actual 
plans : they are either from rough sketches made during an inspection of the 
works in my note-book, or have been in some cases constructed diagramatically, 
to render principles intelligible rather than to give exact representations. 
2 E 
