At first nothing but the coal was dumped into the furnace, the ore and limestone being charged with iron pans similar to the baskets formerly used at charcoal furnaces; the limestone was broken quite small.
After the success of this furnace was assured, furnaces in which mineral fuel (either anthracite or coke, or a mixture of the two, with an occasional use of raw bituminous coal) was exclusively used rapidly increased. Various changes and improvements naturally took place as time passed and experience was gained; but year by year the volume of iron smelted by mineral fuel increased relative to that made by charcoal, until in 1889 it reached the grand total of 7,871,779 tons, while "the make" of the charcoal furnaces amounted to but 644,300 tons.
Notwithstanding the practical demonstration by David Thomas that mineral coal could be successfully used for smelting iron, charcoal furnaces continued to be built. The general appearance of such furnaces as were erected during the fifteen years following the year 1840 is well represented in Fig. 32, of which Fig. 33 is a vertical section. As a rule they were no better in idea, and but little in execution, than those described by Swedenborg a century before; but, after the year 1855, the construction of furnaces began to receive more careful attention, and by the year 1860 the best-informed metallurgical engineers (whose profession was just beginning to be recognized) had discovered that uncouth bulk and crude workmanship were not desirable features in a furnace for the making of pig iron. Yet, nevertheless, some of the stragglers who are always found hovering in the rear of the grand army of progress, and who never know what is going on at the
- Nevertheless, the actual total production of charcoal iron is found to be increasing, as there were but 348,954 tons made in 1856, little more than half the product of 1889. The modern charcoal furnace produces much more iron per year than those constructed thirty-four years ago. The total output of charcoal iron for 1889 was made in 63 furnaces, which would require an average annual production of 10,227 tons per furnace; while in 1856 the total output of charcoal iron came from 416 furnaces, which therefore produced an annual average of but 838 tons per furnace. This calculation is based upon the supposition that all the furnaces reported in 1856 were in operation. Of this there is a little uncertainty; but, after making the most liberal allowance for this, it is still evident that the average annual output of the modern charcoal furnace is many times greater than that of the furnace as constructed in 1856.
A similar calculation applied to the production of anthracite iron (including that made with a mixture of anthracite and coke) shows that in 1889 each furnace produced 18,465 tons of iron, while in 1856 each furnace made but 3,268 tons, or, in other words, the furnace of to-day produces 5fo times as much as that erected thirty-four years ago.
By a comparison of the old bituminous and coke furnaces with those of our time using the same fuels, we learn that in 1856 the average annual output of this class of furnace was 1,61*7 tons, and that in 1889 the average make of the bituminous and coke furnaces was 34,188 tons. From these figures it appears that the furnaces of 1889 were twenty-one times more productive than those of 1856.