MANUAL OP FISH-CULTURE. 



41 



of tbe» lateral compartments, and filters through the gravel into the 

 opposite* compartment, from which it is taken by a plank aqueduct, 6 

 by () inches, to the hatchery. Under the conditions described, and with 

 a fall of about 1 foot from supply to discharge, this filter discharges 

 over 300 gallons of water per minute into the aqueduct — water not abso- 

 lutely pure, but sufficiently free from coarse dirt for the purpose. In 

 many cases, where small quantities of water are used, it is customary to 

 filter through flannel screens in the hatchery, and such filters do very 

 good service. They can be introduced into the egg-troughs, or by 

 running them lengthwise of a trough a very large volume of water can 

 be filtered. 



Gravel Filter. 



/(, a single long comiiartiuent for filtered water. 

 i,j, racks to hold gravel in place. 

 i is in 5 sections, movable, and can l)e taken out 

 when gi'avel is to be renewed. 

 k, I, sluices near bottom for cleaning out. 

 ■)ii, wa8tewaJ^ 

 *!, aqueduct to hatchery. 



o, conduit from brook. 



b, gate, swinging on pivot at c, to change 



direction of water. 

 (/, direct branch of conduit. 

 e, reverse branch of conduit. 

 /,/,etc., a single long compartment for unfiltered 



water. 

 g,fl,ftc., compartments occupied by gravel. 



A form of filter that has given good satisfaction at the Craig Brook 

 station through five years of service consists in a series of graduated 

 wire screens, through which the water passes upward, first through 

 the coarser, and then through the finer screens, with provision for the 

 reversal of the current for cleaning purposes. By reference to the 

 above plan and section, it will be seen that the water is brought to 

 the filter through a plank conduit, and is admitted to the filter through 

 either of two gates that swing on hinges, one for the direct flow and 

 the other for the reversal. The direct flow is first into a receiving 

 chamber, which extends under the screens, then upward through the 

 wliole series and out at the top, overflowing into a catch-trough, from 

 which it is distributed as desired. In cleansing, the supply-gate is 

 closed and the otlier one opened, and at the same time the sluicegate 

 at the bottom is opened; the water then flows in full volume upon the 

 screens and down through them, carrying all the intercepted debris 

 into the lower chamber and out through the sluice-gate. 



