CENTRIFUGAL PUMP DREDGING IN N.S.W. CXXIX. 
Department, for calculation purposes, to estimate 20 cubic feet to 
the ton, the material being chiefly sand which averages 112Ibs. 
per cubic foot. The number of tons pumped per day by the 
“Groper” is readily arrived at, as the silt is all brought alongside 
in punts and dumped, the hopper capacity in cubic feet of each 
punt being known. With the other sand pumps where original 
bottom is dealt with, the known duty of the pump per hour has 
to be relied upon and be multiplied by the number of engine 
hours worked at full speed. It has not been found practicable 
to estimate the quantity pumped by measuring the area reclaimed, 
because the land improved is usually so soft and spongy that the 
depth of sand or silt deposited cannot be reliably obtained. To 
ensure good work it is desirable to carry on two reclamations by 
working a month at each alternately, as successive layers thereby 
part with moisture by draining, and by being subjected to the 
influence of the winds and the heat of the sun. In reply toa 
question asked by one of the members who inspected the work of 
reclaiming at Rozelle Bay, it was stated that the probable pressure 
on the “‘Neptune’s” delivery pipe near the pump was at that time 
about 6ibs. per square inch. This was tested afterwards by fiixng 
@ pressure gauge at the pump, which showed 9 bs., while at 300’ 
away from the vessel a pressure of 2 Ibs. was indicated, the total 
length of pipe at the time was 800’. Respecting Mr. Allan's 
question as to power, the indicated horse power of the **Groper’s 
engines as taken on the 4th August last was 244 horse power, 
when dredging to a depth of 18’, and delivering silt a distance of 
1,250’ through a 20” pipe, The material dealt with was lifted to 
a height of 16’ above water level, and the quantity sent on shore 
was 400 tons per hour.. The velocity of the discharge was 114’ 
Per second. The percentage of solid material in the mixture 
dredged and delivered varies from 20 to 40 per cent. The great. 
Mississippi dredge “Beta’s” percentage is given as from about 
20 to 34, but the distance is only 1,040’. The following records 
would be useful in connection with the paper :— 
9—Oct, 21, 1896. 
