Mr. Wood then proceeds to show how the noise caused by the blast—how, in fact, the blast itself, might be effectually prevented by adopting the expedient employed in the Wylam engine; which was, to send the exhaust steam, not into the chimney (where alone the blast could act with effect by stimulating the draught), but into a steam-reservoir provided for the purpose. His words are these:
"Nothing more is wanted to destroy the noise than to cause the steam to expand itself into a reservoir, and then allow it to escape gradually to the atmosphere through the chimney. Upon the Wylam railroad the noise was made the subject of complaint by a neighboring gentleman, and they adopted this mode, which had the effect above mentioned."[42]
It is curious to find that Mr. Nicholas Wood continued to object to the use of the steam-blast down even to the time when the Liverpool and Manchester Railway Bill was before Parliament. In his evidence before the Committee on that Bill in 1825, he said: "Those engines [at Killingworth] puff very much, and the object is to get an increased draught in the chimney. Now (by enlarging the flue-tube and giving it a double turn through the boiler) we have got a sufficiency of steam without it, and I have no doubt, by allowing the steam to exhaust itself in a reservoir, it would pass quietly into the chimney without that noise." In fact, Mr. Wood was still in favor of the arrangement adopted in the Wylam engine, by which the steam-blast had been got rid of altogether.
If these statements, made in Mr. Wood's book, be correct—and they have never been disputed—they render it perfectly clear that George Stephenson invented and applied the steam-blast for the express purpose of quickening combustion in the furnace by increasing the draught in the chimney. Although urged by Wood to abandon the blast, Stephenson continued to hold by it as one of the vital powers of the locomotive engine. It is quite true that in the early engines, with only a double flue passing through the boiler, run as they were at low speeds, the blast was of comparatively less importance. It was only when the improved passenger engine, fitted with the multitubular boiler, was required to be run at high speeds that the full merits of the blast were brought out; and in detecting its essential uses in this respect, and sharpening it for the purpose of increasing its action, the sagacity of Timothy Hackworth, of Darlington, is entitled to due recognition.
(Colliery Whimsey)