In continuing our account of the process of obtaining iron in the smelting furnace, we omitted to notice that the blowing apparatus delineated in connexion therewith, has, in a great measure, been superseded by improved mechanism of that kind. The pumping cylinder, by an arrangement of valves well understood, is made to draw air on both sides of the piston, so that whilst the air enters on one side it is forced out on the other into the regulating vessel, from whence it is usually conducted into the furnace by two or three distinct pipes and tuyeres. But a most ingenious arrangement of blowing cylinders was invented by Mr. Paterson, of Lanark, which is described and figured in the article Blowing Machines, wherein several others are given. Water bellows have been extensively employed, but the objection to these has been the humidity which the air acquired by the spray; to remedy this defect, the air is forced into a dry regulator, which is simply a large airtight metal box, about 10 feet square and 40 feet long.

At Bradley iron works they have a regulating cylinder of still greater dimensions.

The uniform elasticity which the air acquires in these great chambers causes it to issue in a constant equalized blast.

The blowing of heated air has recently been introduced at several foundries, and likewise at the Clyde iron works. It is the invention of Mr. J. B. Neilson, of Glasgow, whose patent was enrolled in March, 1829, and is designated an improved application of air to produce heat in fires, forges, and furnaces, where bellows or other blowing apparatus is required. He proposes that the air supplied by any kind of machine shall, before it enters the furnace or cupola, be made to pass through an air-vessel heated to very high temperature, a red heat if possible, by which means a current of hot air will be thrown on the fire instead of the cold current usually employed. It is recommended that the air vessel be surrounded with some non-conducting substance, and imbedded in masonry. The capacity of this vessel for a smith's forge he recommends to be about 1,200 cubic inches, and for a cupola or blast furnace, about 10,000 cubic inches. It was much doubted whether the increased temperature of the fire thus blown would produce advantages equivalent to the expense of constructing the air vessel and keeping it at the requisite heat; and as respects the smelting of iron in particular, the theory seemed opposed to the well-known fact that a much larger quantity of iron is yielded by the blast furnaces in the winter season, or when the air is cold, than during the summer season, when the air is warm.

The experiments at the Clyde iron works, have however been reported most favourably of, and the saving of coal attending it is so great, that it was stated, in the Glasgow Chronicle, to be calculated to accomplish a saving in the consumption of this island to the amount of 200,000f. annually. At the Clyde iron works the air was heated to 220° Fahr, before it was discharged into the furnace; an effect which was produced by the expenditure of only one-eleventh part of the cost of fuel it takes to heat it to the same temperature in the blast furnace, which may be accounted for by the circumstance that Mr. Neilson's air vessel is heated by coals, while the blast furnace is heated by coke. Should further experience in this invention confirm the views of the patentee, it may be regarded as a valuable improvement in metallurgic operations.