The first mode of ventilation used was, of course, "natural," caused by elevating the "upcast," or exit, above the "downcast," or inlet. The next mode appears to have been by means of "waterfalls," creating a moving column of air by the means of falling water into the mine or shaft. The third, and that now generally in use, is the "furnace," which creates a draft by rarefaction, causing a rapid exit of the vapors or foul air of the mine, and a consequent influx to fill the partial vacuum. The fourth may be styled "the steam -jet,". caused by the momentary impulse of rushing steam against, or in, the moving column of escaping air, which, of course, increases the movement at the point of vent; but in deep shafts the effects are lost, or partially so, before the column reaches its exit, from the fact that the steam loses its elasticity the moment it condenses. Steam acts like a wire spring, losing its power as soon as its elasticity is destroyed or at rest, which is quite the reverse of the furnace mode of ventilation.
The fifth and last mode of ventilation we shall mention is "mechanical," caused by the operations of a fan or other machinery, which draws the foul air from the mines, and, consequently, the atmospheric air fills its place: This mode we think the most perfect in use, and is now fast superseding all others.
Since the age of improvement has not gone by, we may mention a late invention in the economy of mining which may fairly be classed with the most important of the past or present in this respect,—the application of machinery to the work of mining in place of the thousands of men who now dig our coal by the most tedious and slavish labor known.
A great many coal-cutting machines are now in successful use, driven or operated by steam, water, or compressed air. Their universal application to all bituminous or moderately flat veins, where mining is extensively carried on, is only a matter of time. Not only their cheapness and supe rior effectiveness entitle these "iron miners" to favor, but a means is offered of working smaller seams, and deeper, warmer, and more gaseous basins; since the air they breathe—when worked by condensed air—improves instead of vitiates the mine.
In the process of manufacturing iron, the improvements did not cease with the change from charcoal to coke. It was but the dawn of the great iron-trade of Britain, and the mode was as primitive as the times.
Furnaces increased size and capacity. From 5 they increased to 10 tons per week, and from 10 tons per week they were soon increased to a production of 50 tons, which was about the mean of the 280 furnaces in blast during 1826. But the rapid increase from 1790 to 1826 was small in comparison with the increase of production from 1826 to 1850, or the decrease in the comparative prices. Some of this increase during the later period, as in the former, was owing to the enlargement of the furnaces, the improvement in machinery, and the greater experience and intelligence of the iron-masters. But the great improvement, and the one more than all
others which has influenced the iron-trade, was the invention and applica tion of the hot blast.
Its influence on the coke-iron was truly wonderful, but it was the soul of the anthracite blast-furnaces; without its aid the hard stone-coal of Wales and Pennsylvania—the pure, natural cokes—would have been unavailable for the production of iron.
As an instance of the great benefits derived from the use of hot blast in coke, we may note the influence on the productions of the Clyde Iron Works, Scotland.
At these works, in 1829, the cost of the coke, iron, and limestone required to produce one ton of iron by cold blast was k'8 4s.; but in 1833, when the hot blast was in full operation,—having been introduced in 1831, —with a temperature of 612° Fahr., the cost of making the ton of pig, including labor, Sic., fell to £3 6s.; while the productions of the furnaces were nearly doubled. The cost, however, of pig iron in Great Britain has been put at £2, or $10, per ton, of late years.
In 1850 the cost at Merthyr,* in Wales, is given at £3 Os. 5d.; at Glasgow, Scotland, at £2 17s. 9d.
The gross make of coke in Great Britain in 1860 is estimated at 6,000,000 tons; of this amount, 2,500,000 were the products of the Northern coal field in Durham and Northumberland. The present gross production of pig iron in Great Britain is estimated to exceed 5,000,000 tons per annum. To produce this, not less than from 21 to 3 tons of crude coal per ton are required as a mean, which would exhaust about 3000 acres of a four-foot seam of coal per annum.
"It has been calculated that an acre of coal four feet in thickness pro duces as much carbon as 115 acres of full-grown forest; and that a bushel of coal,-84 pounds,—consumed carefully, is capable of raising 70,000,000 pounds one foot high; and that the combustion of two pounds of coal gives out power sufficient to raise a man to the summit of Mont Blanc, 15,668 feet high.
"The aggregate steam-power, estimated at 83,635,214 horse-power, of Great Britain and Ireland alone, is calculated as equal to 400 millions of men, or equal to twice the power of the adult working population of the Wonderful as it may seem, the above calculation is practical; and we have no doubt but Great Britain really possesses a dynamic strength in iron and coal to the extent named, since we always calculate one horse power as equal to the physical strength or exertion of seven men, which would give a laboring force of over 585,000,000 of men. To this, even the vast population of China is insignificant as a physical power or an industrial and productive force; but when it comes to forcing a steamship of 20,000 tons across the Atlantic at the rate of 300 miles per day, or a train of 400 persons at a speed of 60 miles an hour, there is no comparison in brute force.