The flues or tubes of a boiler should be cleaned about once a week, with a brush or scraper. In case incrustation has formed in them, they can be cleaned by a jet of steam from a rubber hose. A boiler should be blown down and cleaned, under ordinary circumstances, about once a month. The fire should first be hauled; and then, if possible, it is best to let the boiler stand until the water becomes tolerably cool, say for 12 hours, after which the water may be allowed to run out. Then remove the man and handhole plates, enter the boiler, and clean it with scrapers and brushes in every part that can be reached. It should then be washed out with cold water from a hose, and this washing with a hose is the only means of cleaning those parts of a boiler that can not be reached by hand. There are many boilers into which a man can not enter, and of course these can only be washed out. 'When the fire is hauled, all leaks in the boiler should be repaired. Leaky parts exposed to the fire must have hard patches riveted on; in other places soft patches secured by bolts can be used, each patch having a lip around it, and the joint being made with a putty composed of red and white lead. Leaky rivets or seams can sometimes be made tight by calking. Small leaks around the ends of tubes can often be stopped in the same way, but as a general thing a leaky tube must either be replaced or plugged. To plug a tube, drive a white-pine plug tightly into each end, and cut it off even with the tube-beads; then pass a bolt through the tube, with cup washers on each end, and screw it up tightly, putting putty under the washers. B.