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43. Suppose we have two furnace-pits, the first 260 feet deep, the second 655 feet deep.

To arrive at the horse-power of furnace-ventilation, we must find the pressure producing it.

First, Barometer of the first pit, 30.3"; temperature of downcast, 55°; of upcast, 240°. The pressure, therefore, of the downcast in pounds per square foot, is

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20.312

14.936 5.376 pounds as the pressure per square foot for ventilating pressure, and this pressure will give us, say, 30,358 cubic feet of air, then the horse-power will be

30358 x 5.376

33000

4.94 horse-power in the air.

Second, Mean barometer, 30.6′′; temperature of down

cast, 58°; temperature of upcast, 117°; then the pressure in pounds per square foot is, for downcast,

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Hence, for ventilating pressure, 51.37946.116 = 5.263 pounds per square foot; and this pressure gives 48,230 cubic feet of air per minute, which, reduced, gives us 7.69 as the horse-power in the air.

These two furnaces ventilated the Hollingwood pits. The No. 1 furnace used 3 tons 12 hundred weight of coal in 24 hours, or 68 pounds per hour per horse-power in the air. No. 2 furnace used 3 tons 1 hundred weight per day, or 37 pounds of coal per hour per horse-power in the air. The two furnaces circulated 78,588 cubic feet of air, with a horse-power of 12.63.

A Guibal Fan was afterwards substituted to take the place of these furnaces, the ordinary speed of which was sixty revolutions per minute. The average quantity of air circulated at this speed was 106,680 cubic feet; the pressure, 2.8 water-gauge, or 14.56 pounds per square foot.

120

MINE VENTILATION.

§ 43.

Tabulated results of the above calculations show the economy of fan over furnace ventilation. The wages and price of coal are those regulated by the English market at the time of the writing, reduced to UnitedStates money.

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k = co-efficient of friction, 0.0217 of a pound at a velocity of 1,000 feet per minute.

p = pressure in pounds per square foot of sec

v

=

tional area.

velocity of the air in feet per minute.

w= water-gauge.

q quantity of air circulating, in cubic feet, per

и

HP

=

minute.

= units of work applied to circulate the air.

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122

MINE VENTILATION.

$ 44.

Then the following formulas for friction of air in

mines may be deduced:

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