The first stage of the process invented by Mr. Strong is so nearly the same with that already described that a repetition is unnecessary, the furnace being fired up until the loose brick contents of the secondary chamber or superheater are at a white-heat, when, as before, gas-making is commenced. But here the current of the process, so to speak, is reversed. Instead of letting the jet of steam in at the bottom of the furnace, we let on steam at the other end of the system, i. e., at the top of the superheater, and pass it directly downward through the mass of white-hot fire-brick. This raises the steam to a perfectly invisible gas, hotter than devouring flame, as it rushes from the superheater, through an extra flue, into the upper part of the furnace. There it meets a shower of anthracite coal-dust instead of petroleum, sifted down into the furnace from above, and literally burns it up with intense combustion—precisely as coal-dust would be devoured in the fierce flame of the blast-furnace seven times heated, except that the oxygen of this combustion is supplied entirely by a steam-instead of an air-blast. In other words, the steam furnishes both heat and oxygen for the instant conversion of the coal-dust to carbonic acid, with the consequent release of its own prodigious volume of hydrogen. Under their own increased pressure, the gases continue without pausing, down though the mass of glowing coals. In making this passage, the carbonic acid takes up a double portion of carbon from the hot coals and becomes carbonic oxide—the powerful heating gas so often seen burning in a lambent violet flame on the surface of anthracite fires when the air is let in on them. As there is no access of atmospheric oxygen to the furnace, there is no opportunity for the combustion either of this gas or of the freed hydrogen, and accordingly both pass out together at the bottom of the furnace, through a pipe which conducts to the gas-holder.
The product of this process, before purification, has been rigorously analyzed by the several methods, by Professor Gideon E. Moore, Ph. D., and proves to be 52·76 per cent, pure hydrogen, 35·88 per cent, carbonic oxide, and 4·11 per cent, marsh-gas, making nearly ninety-three per cent, of the whole volume in these powerful calorific agents, leaving only six to seven per cent, of incombustible waste (carbonic acid and nitrogen). Wurtz also gives substantially the same proportions, in Johnson's "Cyclopædia."
The purity of this fuel is a consideration nearly sufficient of itself to revolutionize the manufacture of iron, and especially of steel, for which, in its perfection, few if any mineral coals are sufficiently free from such troublesome ingredients as sulphur, phosphorus, etc.; but of this further on.
With respect to comparative calorific values, Professor Moore's report shows, by rigorous calculation, that the Strong fuel-gas will produce 2·78 times the practical effect of the amount of coal consumed in its manufacture, supposing the same coal were burned directly by the
