FILTER-BED. 139 



a safe distance, say, one hundred feet from the factory, 

 ordinary tile may be used, as they are less expensive. 



2. Excavate a bed about twenty feet by twenty 

 feet to a depth of two or three feet, using the dirt to 

 bank the sides, making the bed four to six feet deep. 

 In the bottom of the excavation place from two to 

 four rows of four-inch drain tile, covering the joints, 

 and giving them a fall of two to four inches to the 

 further side of the bed, where they may empty into 

 a ditch, stream, or bay. Then fill in the excavation 

 on top of these tile with coarse gravel. Make the 

 surface smooth and sloping towards the farther side. 



3. A wooden trough may be used for distributing 

 the sewage over the surface of the bed. 



4. Rake the surface occasionally, and keep it free 

 from weeds. In the winter the surface may be fur- 

 rowed and the furrows covered with boards to pre- 

 vent freezing. 



5. The top three or four inches may have to be 

 renewed with fresh sand or gravel every four or five 

 years. 



6. Where possible the " blow-off " on the boiler may 

 be connected with the factory drain to clear it of 

 grease, dirt, etc. Hot solutions of lye should be 

 poured down the drain at least once a week. 



