_3dly_, That 1-6th part of the above extent is sufficient for pillars to support the roofs of the mines, &c.
And, _4thly_, It appears, by experiments, that a cubic yard of coal weighs 1 ton, or 20 cwt.
The total consumption of coal from the rivers Tyne and Wear known from the register to be 2,300,000
The number of tons in the above quantity taking the London chaldron at 27 cwt. is 3,100,000
Now a ton weight of coal is estimated to occupy in the earth the space of one cubic yard.
The number of cubic yards in the square mile is 3,097,600
The beds or seams of coal are, on an average, 4 feet and a half in thickness, which increases the above number of cubic yards in the square mile by half the number of square yards to 1,548,800
And hence the square mile of the beds or seams of coal we are describing contains, of cubic yards and tons of coal 4,645,000
A deduction of 1-6th for pillars to support the mine, &c. 800,000
The number of tons per square mile 5,445,000
We have already mentioned the length and breadth of the seams of coal to be equal to 20 miles by 15, making an area of 300 square miles, and consequently a source of consumption for 375 years.
It may be objected to the universality of our conclusion, that the price of coals, differing very much in different places, will occasion a variation in the expence of the new mode of illumination. But there are two reasons why this should have less place, because we find, in Mr. Murdoch’s statement, page 69, that of 600l. the estimated yearly expence of lighting the cotton mill, 550l. consist of interest of capital, and tear and wear of apparatus, leaving the cost of coal only 50l. a sum so trifling, when we reflect that it replaces 2000l. worth of candles, that the price of coal, even where it is highest, can but slightly affect the general profits.[32]
[32] See, also, Mr. Ackermann’s statement, page 71.
_2dly_, The coal, by yielding the gas and other products,--namely, tar, pitch, ammoniacal liquor, &c. of which we have treated already, is converted into a substance, increased in bulk, and in the power of producing heat, namely, coke; and as a manufactory generally requires heating as well as lighting, there will be a gain both ways. The manufacturer, by distilling his coal, instead of burning it as it comes from the pit, will save his candles and improve his fuel. One effort at the outset, in erecting a proper apparatus, will reduce his annual disbursement, for these two articles of prime necessity, much in the same manner, (though in a far greater degree) as the farmer gains by building a thrashing machine and laying aside the use of the flail.