(26) J. J. asks: Which tire makes a wheel the strongest, 1.25 x 0.50 inch iron, or 1.25 x 5⁄16 steel tire? A. The steel tire will be the strongest, comparing good qualities of steel and iron.
(27) E. L. W. asks: Is a ton (2,000 lbs.) of first class coke equal in heat giving power to a ton (2,000 lbs.) of coal? If not, please give me the relative value of coke and coal in heat giving power? A. Calling the evaporative power of good anthracite coal 1, good bituminous coal rates at about 0.92, and coke from 0.89 to 0.95.
(28) J. W. S. asks what to impregnate paper with to give it an agreeable smell while burning. A. You may try a strong ethereal or alcoholic solution of benzoin, tolu, storax, olibanum or labdanum. To burn well the paper should first be impregnated with an aqueous solution of niter and dried.
(29) M. G. asks whether hydrogen and oxygen can be produced as rapidly and copiously in the decomposition of water by the galvanic battery as by the action of sulphuric acid on zinc or lead in the one case, and by heating chlorate of potassa in the other. A. Yes, with a very powerful current.
(30) T. G. H. asks for names of useful treatises on mechanical movements. A. "Scientific American Reference Book," and "507 Mechanical Movements."
(31) R. B. T. writes: We have just set up a new engine; the cylinder is 8 x 12, has a common slide valve. We think the valve is too short; it is set 0.125 inch open when on center, takes steam 10 inches before cutting off; the exhaust is very free. The engine runs about 110 revolutions per minute. We think we could save steam by using a longer valve, and cut-off about ⅝ stroke, and make the exhaust space in the valve shorter, so that it will shut in a portion of the exhaust and form a cushion for the piston. About how much of the exhaust can we shut in without overdoing it? A. You can obtain a good action by making the ratio of compression equal to the ratio of expansion, with the proviso that the final cushion pressure must not exceed the initial pressure.
(32) D. B. L. writes: Our boiler after being repaired was tested at 110 lbs. cold water pressure. Three days after it gave out where it was repaired at 58 lbs. steam pressure. To find the leak we put on 80 lbs. cold water pressure, and could not find it. We then put steam pressure at 40 lbs., which made the leak very great, whereas with cold water pressure we could find none. Can you explain it? A. The phenomenon is probably due to the change of shape in the boiler when heated.
(33) F. C. writes: Our engine is a plain slide valve engine, 24 x 9, steam following almost to end of stroke. How shall I make a valve to cut off at ¾? Our exhaust now is 1 inch, steam ports 0.75, bridges 0.75. Length of valve 4½ inches, cavity 2⅜, travel of valve 2 inches. Will I have to enlarge the steam chest; the valve uses the whole length of it now? A. As the length and travel of valve must be increased, it will be necessary to lengthen the steam chest, unless you can apply an independent cut-off valve.
(34) T. P. writes: A small basement room 9 feet high is to be heated by a furnace in an adjoining room. By carrying the hot air pipe through the partition midway between the floor and the ceiling it will stand at an angle of about 45°. If carried through at the top of the room it will of course be nearer vertical. In which position of the hot air pipe will the room be most easily heated? A. Place the hot air pipe in the position first described. Take the cold air from a point near the floor through a flue opening above the roof.
(35) G. M. P. asks: What is a good and cheap substitute for salt for raising the temperature of water to 230° Fah.? A. An oil bath is often used instead. Chloride of calcium will answer as well as salt, though not so cheap.