─────┬─────────────┬────────────────┬─────┬───────────┬──────────────
│ Fire─box │ Hearth │ │ │ Tons Ore per
Year.│ Dimensions. │ Dimensions. │Stack│ Capacity. │ Ton Coal.
─────┼─────────────┼────────────────┼─────┼───────────┼──────────────
1878,│4' 6" × 5' │ 9' 8" × 15' │2' 9"│12 tons. │2·4 tons.
1882,│4' 6" × 5' │10' 4" × 17' 10"│2' 9"│17 " │2·43 "
1887,│4' 6" × 5' 6"│12' 8" × 21' 2"│3' 0"│24 " │2·67 "
1891,│4' 6" × 6' │14' 2" × 24' 4"│3' 0"│28 " │2·8 "
1893,│5' × 6' 6"│16' × 30' │3' 6"│35 " (43)‡│2·7 " (3·3) ‡
1894,│5' × 6' 6"│16' × 35' │4' 0"│ (50)‡│ (3·7) ‡
1903,│5' 6" × 10' │20' × 50' │5' 5"│ (70)‡│ (3·1) ‡
1910,│8' × 16' │19' × 116' │ .. │ (275)‡│ (4·66)‡
─────┴─────────────┴────────────────┴─────┴───────────┴──────────────
‡ The charges of calcines were fed whilst still red hot.
This practice has been continued in modern smelter work, the
developments being in the direction of attempting to melt the largest
possible quantity of charge in one furnace as rapidly as possible.
This has been found to depend upon the rapidity with which the fuel is
burned, and the enlarging of the fire-box had a specially important
influence in effecting this rapidity of combustion.
Then, with the size of grate fixed and the most efficient burning of
the fuel arranged for, the capacity of the furnace depends simply on
increasing the area of the hearth to as great an extent as the heat
generated is capable of maintaining at the desired temperature.