(2) The substitution of coke for charcoal proceeding pari passu with improved methods of smelting yielded an average output for coke-fed furnaces of 903 tons in 1788. To this epoch belong also Cort's inventions for puddling and rolling (patented 1783-84), which revolutionised the production of bar-iron.
(3) The introduction of Watt's double-power engine in 1788-90. In 1796 the production of pig-iron was double that of 1788, and the average output per furnace raised to 1048 tons.
(4) The substitution of hot for cold blast in 1829, effecting an economy of coal to the extent of 2 tons 18 cwt. per ton of cast-iron.
(5) The adoption of raw coal instead of coke in 1833, effecting a further reduction of expenditure of coal from 5 tons 3-1/2 cwt. to 2 tons 5-1/4 cwt. in producing a ton of cast-iron.
These were the leading events in the establishment of the iron industry of this country. The following table indicates the growth of the production of English iron from 1740 to 1840:—
| Year. | No. of Furnaces. | Average Output. Tons. | Total Produce. Tons. |
| 1740 | 59 | 294 | 17,350 |
| 1788 | 77 |
909 coke 545 charcoal | 61,300 |
| | 909 coke 545 charcoal | | |
| 1796 | 121 | 1048 | 125,079 |
| 1806 | 133 | 1546 | 258,206 |
| 1825 | 364 (261 in blast) | 2228 | 703,184 |
| 1828 | 365 (277 in blast) | 2530 | |
| 1839 | 378 | 3592 | 1,347,790 |
Here we see that economy of power rather than improved machinery is the efficient cause of the development of industry, or more properly, that economy of power precedes and stimulates the several steps in improvement of machinery.
The substitution of coke for charcoal and the application of steam power not merely increased enormously the volume of the trade, but materially affected its localisation. Sussex and Gloucester, two of the chief iron-producing counties when timber was the source of power, had shrunk into insignificance by 1796, when facilities of obtaining coal were a chief determinant. By 1796, it is noteworthy that the four districts of Stafford, Yorkshire, South Wales, and Salop were to the front.
The discovery of the hot blast and substitution of raw coal for coke occurring contemporaneously with the opening of railway enterprise mark the new interdependence of industries in the age of machinery.
Iron has become a foundation upon which every machine-industry alike is built. The metal manufactures, so small in the eighteenth century, attained an unprecedented growth and a paramount importance in the nineteenth.