bined by that of the boiler alone; or otherwise expressed by dividing the amount of combustible burned by the amount fired. Q. What is the effect of high initial gas temperature on boiler efficiency? A. To increase the efficiency of the heating surface. CHAPTER XL 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 in 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 six per cent water in the worst cases, and an average not over 12. 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 9912 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 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: Rate of combustion. Minimum evaporation. Q. At the above rates, and figuring a horse-power to be represented by 341/2 pounds of steam from and at 212 deg. F., how much tube fire-surface is necessary for a horse-power? A. A little over two square feet. Q. Putting it the other way about, what part of a horse-power 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 *Pounds of coal per square foot of grate per hour. 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. Give some recent concrete figures of the steaming capacity of a fast passenger engine? A. The K 4 s engine of the P. R. R., referred to elsewhere, using superheater, evaporated from 18,157 to 87,414 lbs. of water (reckoned from and at 212 deg.; actual evaporation 14.397 to 65,400 lbs.) per hour; being actually 205.7 to 920 lbs. per hour per square foot of grate (from an at 212 deg., from 259.5 to 1,248.8 lbs. ;) per square foot of heating surface 3.73 to 17.97 lbs. per hour. Q. Show the relation between indicated horse-power and water consumption on a recent heavy passenger locomotive. A. Taking a Penna. R. R. engine of type K 4 s, we have about 18.5 lbs. of steam per i.h.p. hour at 1,600 i.h.p; 16.1 at 1,900. Between 900 and 2,800 the rates are under 18 lbs. At minimum power (3,250 i.h.p.), the consumption increases to about 20 lbs. But on a K 2 s a engine the water rate decreased steadily from 19 lbs. at 900 i.h.p. to 17 at 2,600 i.h.p. Q. What is the relation between water rate and piston speed under good recent conditions? A. Taking the Penna. R. R. K 4 s machine, we have the water rate decreasing with the piston speed from 19.6 lbs. per i.h.p. hour at 560 feet a minute, to 15.3 lbs. at 1,670 feet. The same character of relations exist in the K 2 s a type on the same road. Q. Give some data concerning the various steam pressures in a recent locomotive. A. As under, the tests being the same for which temperatures are given elsewhere, Penna. R. R. engine, K4s type: Q. Give some data concerning comparative performance of a recent locomotive. A. Taking the K4s type of the Penna. R. R., we have the following figures: |