A saw-mill owner solves the problem of using saw-dust as fuel as follows. His boiler was a return tubular, 14 feet 6 inches long and 54 inches in diameter, with 64 three-inch tubes, and brick firebox 48 x 56 x 27 inches high; bridge-wall was 7 inches at centre, rounded to the sides of boiler. He states: "I lowered the bridge-wall 13 inches (keeping the same circle as before), lowered the paving in rear of firebox to a level with the grate-bars, and obtained a barrel of furnace-slag from 3 to 7 or 8 inches in size and 1 or 1-1/2 inches thick, which I placed on the grate-bars, about half covering them. I fired with wood; and when the slag got heated, I threw in the sawdust, which burned very well but smoked fearfully (clouds would arise from the smoke-stack). I then introduced a 2-inch pipe, with about fifty 1/4 -inch holes, directly behind the bridge-wall, leaving both, ends of pipe open; after which, I never had a particle of trouble either in keeping up steam or in burning up the smoke. Not even in firing up did 1 ever see any smoke come out of the stack, which was 30 feet high and 32 inches square, enlarged near top and to the top to 36 inches inside measurement. I forgot to state that I covered the top of boiler with sheet-iron, then laid brick on it, covering the interstices with sand. The sheet-iron was to prevent the sand from wedging off the wall when the boiler expanded." A system of alternate firing, and with grates so arranged as to permit some charred fuel to fall through and burn in the ashpit, gives the best results.