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Summary of the Steam Log. From New York to Liverpool.

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Means of means, 222612 265 53 943 3080 15.85 14-028 7978
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Remarks on the Steam Log.

11.666

An inspection of the preceding "summary," shows the voyages from New York to Liverpool to be on an average 24 hours and 12 minutes shorter than the average of the voyages from Liverpool to New York. The length of the route or distance run can be taken to be the same in both directions, the means by observation differing only 14 miles, or less than half of one per cent. of the lesser distance; but the voyage from New York to Liverpool required on an average 7738 less revolutions of the wheels, than the average voyage from Liverpool to New York. In the latter case, therefore, the slip of the wheels was 2.99 per cent. more than in the former; the slip in the latter case being 20.86 per cent., and in the former case 17.87 per cent. The consumption of coal also is less in the voyages from New York to Liverpool, by an average of 31 tons; but the consumption of coal per hour is greater by 2214 pounds.

The difference in the performance of the vessel for the easterly and westerly passages, is probably caused by the greater prevalence of westerly winds. The distance from the Battery, New York, to Liverpool, by Mercator and great circle, is 3023 geographical miles; by Mer

cator, 3084 geographical miles. The mean, therefore, of 3080 miles, made by the Arctic, shows very excellent navigation.

Coal. The coal used in the voyages from New York to Liverpool was the Pennsylvania anthracite; in the voyages from Liverpool to New York, the Welch coal of similar chemical composition.

Evaporation by the Pennsylvania Anthracite. The cut-off used in the Arctic was Stillman & Allen's; it was adjustable, and frequently changed within short limits, as circumstances of weather, quality of fuel, &c., required; the object being to run with a wide throttle and maximum boiler pressure. The average point of cutting off was four feet four inches from the commencement of the stroke, and the steam space comprised between the cut-off valves and pistons of the two cylinders, at one end, is, as near as I have been able to obtain it, 25 cubic feet, which I believe is exact. This would make the bulk of steam used in both engines per stroke 451-608 cubic feet. The number of double strokes of piston per minute was 14-403, making the bulk of steam used per minute 13009-02 cubic feet. To this must be added the loss by blowing off in sufficient quantities to maintain the sea water in the boilers at 14 the natural concentration. From the data given in Regnault's experiments, this loss would be as follows-the temperature of the feed water being maintained at 110° Fah., and the average steam pressure in the boilers being 15.6 pounds per square inch above atmosphere, or 30-3 pounds total pressure. The total heat of steam of this pressure is 1158-34° Fah., of which 110° were furnished by the feed, leaving 1048-34° to be furnished by the fuel to the three parts of the water evaporated. The temperature of steam of 30-3 pounds being 252.2° F., and the temperature of the feed 110° F., there was (252.2—110=) 142.2° F. to be supplied by the fuel to the four parts blown out; and

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supplied by fuel, of which 568-80° is 15.32 per cent., and is lost by blowing out, leaving 84-68 per cent. of the fuel utilized in evaporation, and if 84-68 per cent. evaporated 13009-02 cubic feet per hour, 100 per cent. would evaporate 15362-57 cubic feet. The mean of a large number of indicator diagrams gives the initial cylinder pressure 2 pounds less than the boiler pressure, making it 28-3 pounds per square inch, and the relative of bulks of steam of this pressure and the water from which it is 15362.57 generated is as 932 to 1:16.4834, which, taking the weight

932

of distilled water at 62 pounds per cubic foot, becomes 1030-2125 pounds of steam evaporated per minute, or 61812-75 pounds per hour by 8199 pounds of coal, which is 7.539 pounds of steam evaporated per hour from sea water of one and three-fourths the natural concentration, by one pound of Pennsylvania anthracite, with temperature of feed water 110° F.

Evaporation by the Welch Coal.-Proceeding in the same manner with

the Welch coal, with the same point of cutting off, and the same difference of two pounds between the initial cylinder and boiler pressure, and making the necessary alterations for the different total and sensible heats of the slightly different steam pressure; there results an evaporation of 7.653 pounds of steam per hour from sea water of one and three-fourths the natural concentration, by one pound of Welch coal, with temperature of feed water 110° F.

The results from the Anthracite and Welch coals agreeing so very closely, it may be concluded the two fuels are of equal value as generators of steam, an agreement we should also be entitled to expect from their closely resembling chemical constitutions, which compare as follows-Professor Walter R. Johnson being the authority for the Anthracite, and the British Commission of De la Beche and Playfair for the Welch coals from the northern part of Wales:

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PERFORMANCE.--The mean performance of the Arctic for the six voyages eastwardly and the six voyages westwardly, being the average of 3190 hours and 38 minutes steaming, is as follows, viz:

Speed of the vessel per hour in geographical miles of 60823 feet, 11-666 statute miles of 5280 feet,

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Revolutions of the wheels per minute,
Slip of the centre of pressure of the paddles,
Oblique action of the paddles,

Steam pressure in boilers per square inch above atmosphere,
Initial steam pressure in cylinders per sq. in.

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Point of cutting off from commencement of stroke,
Mean effective pressure per square inch of pistons,
Horses power developed by the engines,

Consumption of coal per hour,

Consumption of coal per 24 hours in tons of 2240 lbs.

13.439

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Consumption of coal per square foot of grate surface per hour,

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15.85 pounds.
13.85

4 feet 4 inches. 19 pounds.

2290

7978 pounds.

85.48 tons.

13.571 pounds.

INDICATOR DIAGRAM. The accompanying indicator diagram, (Plate II.) is selected from a large number, to show the average performance of the engines, setting of the valves, &c. It was taken from the top of the starboard cylinder, the engines making 14 double strokes of piston per minute. Steam pressure in boilers above atmosphere, 18 pounds per square inch. Temperature of hot well 113° Fah. Throttle wide.

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