A. Lime is the most common, in some of its compounds, as carbonate or sulphate; magnesia and iron are also found, as is ordinary clay. Q. What are preventives of scale? A. 1. The choice of a water having therein no mineral substances that will be left behind in the boiler when the water has been turned into steam; 2, filtration of the water, to remove substances which are only mechanically contained therein; 3, chemical treatment of the water to make it deposit the mineral substances before it reaches the boiler; 4, chemical treatment simultaneously with its supply to the boiler. Q. Where must the second and the third preventives be resorted to? A. In the station tank or before the water reaches it. Q. What are resorted to to remove scale once it has formed in the boiler? A. Petroleum, and various chemicals which exert a loosening effect on the scale already deposited. Q. Will black oil soften all kinds of scale? A. No. Q. Would lard oil or valve oil help? A. No; it would cause foaming and not affect the scale. Q. How is mud deposit prevented? A. 1. By filtering; 2, by using pure water; or 3, by frequent blowing off, hot. STEAM PRODUCTION. Q. What is the maximum production of steam, in cubic feet per hour, in a medium-sized passenger locomotive? A. It takes about five cubic inches of cylinder capacity per net ton of adhesive work to move a locomotive one inch; and about one-fifth cylinder full of steam for each single stroke of each piston. Supposing 15 inches piston diameter and 20 inches stroke with a 48,000-pound engine with 24,000 pounds of tender and enough cars to make the total train weight 212,000 pounds or 106 net tons, with seven pounds traction per net ton of train, for a speed of ten miles an hour on a straight level track (or 21 pounds on a grade) with 90 pounds of boiler pressure and cut-off at one-fifth, it would take 80 x 5 = 16 cubic inches of steam per inch, 84,480 cubic inches per mile, 8,444,800 cubic inches or 65.35 gallons per hour; to which add 20 per cent for water carried over, etc. Q. What may be said of the quality of steam furnished by locomotive boilers? A. Tests made with a locomotive standing on the test plant, where there was in all probability less foaming and priming than there would be in service on the road (especially if this was more or less rough) showed in the dome less than 6 per cent water in the worst cases, and an average not over 11⁄2. In the steam-pipe the superheating due to wire-drawing reduced this amount one per cent; so that the average quality of steam in the branch-pipe was about 991⁄2 per cent dry steam. Q. What about the evaporation per pound of coal in a locomotive boiler? A. In a constant test, using good coal with 76 per cent fixed carbon and 7 per cent of ash, the evaporation per pound of coal was for different rates of combustion as follows: Q. What is the amount of water that can be evaporated per square foot of fire heating-surface per hour? A. Referring to the steam tests already quoted, the amounts of water per square foot of fire heating-surface per hour, due to the maximum evaporation and rates of combustion above, were as follows: Steam per square foot of heating surface per hour: Q. At the above rates, and figuring a horse-power to be represented by 341⁄2 pounds of steam from and at 212° F., how much tube fire-surface is necessary for a horse-power? A. A little over two square feet. * Pounds of coal per square foot of grate per hour. Q. Putting it the other way about, what part of a horsepower may be obtained in a locomotive boiler from one square foot of surface of the fire side of the tubes? A. Tests have showed from 0.26 to 0.41 horse-power per square foot of fire side of tubes. Q. How does the circulation in a locomotive boiler usually proceed? A. Along the bottom of the barrel from the front end, down the fire-box front, and up the sides and back to the fire-box; but the manner of firing may change this, or even reverse it. Q. What are the results of tests for boiler performance? A. Contrary to the common assumption, large boilers, when forced to maximum power, deliver as much steam per unit area of heating surface as small ones. At maximum power, a majority of the boilers tested delivered. 12 or more pounds of steam per square foot of heating surface per hour; two delivered more than 14; the second largest delivered 16.3. These values, in boiler horse-power per square foot of heating surface, are 0.34, 0.40 and 0.47, respectively. Q. Which steamed best-passenger or freight engines? A. The two boilers holding the first and second place with respect to steam per square foot of heating surface, were those of passenger locomotives. Q. What are the essentials of a good locomotive boiler? A. 1. Reliability and mechanical maintenance-that is, freedom from cracked sheets, leaky seams and flues, leaky and broken stay-bolts. 2. Continuous development of maximum horse-power within the capacity and endurance of the ordinary fireman. 3. An efficiency as near as possible to that of the best. stationary and modern boilers. Q. On what do reliability and low cost of maintenance depend? A. Principally on freedom of circulation around the fire-box. Q. What elements go to facilitate such circulation? A. Depth of box and width of water legs. Q. Should depth be obtained by depth of throat sheet, or by raising the crown sheet? A. By depth of throat sheet. Q. Is the ordinary fire-box calculated to withstand the heat of perfect circulation? A. No; but the better the circulation the less the trouble with the fire-box. Q. What is the best rule for calculating the horse-power of a boiler? A. A boiler has no horse-power. One engine will get three or four times as much power from the steam delivered by a given boiler as another. A common rule is, however, to divide the number of square feet of heating surface by 12, to get the rated horse-power. A boiler which evaporates 342 pounds of water into steam from and at 212° per hour is said to be of one horse-power. WATER TUBE BOILERS. Q. Describe the Robert water-tube locomotive boiler? A. The outside appearance is the same as that of an ordinary locomotive boiler. The boiler proper is formed of a mud drum and a steam drum, connected by three circular uprights. The steam drum is extended to the rear above the fire-box, and is fitted at the top with a steam dome connected by return tubes to a feed-collecting hollow frame at the bottom of the fire-box. The fire-box sides are lined by return tubes close together, expanded in the hollow frame and in the steam drum. The drums are connected by curved tubes, those in front and rear of the fire-box being large steel tubes, and |