The Invention of the Hot Blast in Iron-Smelting

Abstract

HAVING read Mr. E. Wyndham Hulme's letter, together with a copy of the article in the Engineer to which he refers, and the specification of Stirling's Patent No. 4081 of 1816, I cannot see any ground for his supposition that it anticipated Neilson's subsequent invention of hot blast in iron-smelting. Stirling's specification describes and claims what is usually termed the ‘regenerative’ principle in furnaces, whereby heat from outgoing hot products of combustion is transferred to an inflowing air draught; and there is not a single word in it referring to the use of hot blast in iron-smelting. The central idea of Neilson's invention as applied to iron-smelting was that the use of an air blast preheated by combustion of small coal on a separate grate outside the blast furnace would save many times as much fuel inside it, which, paradoxical though it may and certainly then did seem, is nevertheless true; it is obviously different, and never could have been forecasted, from the principle of heat regeneration or recuperation. It was, indeed, one of those flashes of inspiration which sometimes come to a man of genius and through him revolutionise human affairs. In applying his idea at the Clyde Ironworks during the years 1829–32, when its success was so triumphantly demonstrated, Neilson did not use the regenerative principle at all, or indeed any means of preheating the blast described or foreshadowed in the Stirling patent; nor did he use any hot gases or products from the furnace for this purpose. The Stirling patent may be held to have anticipated Siemens' later inventions, but certainly not Neilson's process.