The great modern art of iron working dates from Lord Dudley’s British patent, No. 18, of 1621, which related to “The mistery, arte, way and meanes of melting iron owre, and of makeing the same into cast workes or barrs with seacoales or pittcoales in furnaces with bellowes of as good condicon as hath bene heretofore made of charcoale.” The next step of importance after the blast furnace was the substitution of coke for coal for the reduction of the ore, which was introduced by Abraham Darby, about 1750. Next came the conversion of cast iron into wrought iron. This was mainly the work of Mr. Henry Cort, of Gosport, England, who, in 1783-84, introduced the processes of puddling and rolling, which were two of the most important inventions connected with the production of iron since the employment of the blast furnace. Mr. Cort obtained British patents No. 1,351, of 1783, and No. 1,420, of 1784, for his invention. His first patent related to the hammering, welding, and rolling of the iron, while in his second patent he introduced what is known as the reverberatory furnace, having a concave bottom, into which the fluid metal is run from the smelting furnace, and which is converted from brittle cast iron, containing a certain per cent. of carbon, into wrought iron, which has the carbon eliminated, and is malleable and tough. This process is called _puddling_, and consists in exposing the molten metal to an oxidizing current of flame and air. The metal boils as the carbon is burned out, and as it becomes more plastic and stiff it is collected into what are called blooms, and these are hammered to get rid of the slag, and are reduced to marketable shape as wrought iron by the process described in his previous patent. Mr. Cort expended a fortune in developing the iron trade, and was one of the greatest pioneers in this art. The first notable development of the Nineteenth Century was the introduction of the hot air blast in forges and furnaces where bellows or blowing apparatus was required. This was the invention of J. Beaumont Neilson, of Glasgow, and was covered by him in British patent No. 5,701 of 1828. This consisted in heating the air blast before admitting it to the furnace, and it so increased the reduction of refractory ores in the blast furnace as to permit three or four times the quantity of iron to be produced with an expenditure of little more than one-third of the fuel. [Illustration: FIG. 250.--MODERN HOT BLAST FURNACE.]