If a mass of cast iron be heated until softened, and then _puddled_ (squeezed), the carbon will be forced to the surface, and will there combine with the oxygen of the atmosphere, forming carbonic acid or carbonic oxide gases, and thus pass off. When all the carbon has been parted with, the mass is called Wrought Iron, and may then be welded, when at proper heat, but cannot be melted--_the hottest blast furnace will not melt wrought iron_. Wrought iron at red heat combines rapidly with oxygen, and becomes oxide of iron--thus a joint of stove-pipe thrown into a furnace will never melt, but by contact with atmosphere will change into oxide of iron, and thus be practically lost. This operation is technically called _burning_. If a piece of wrought iron be surrounded by carbon (charcoal) finely pulverized, and the whole enclosed in a sheet iron vessel to exclude the air, and this placed for a sufficient length of time in a furnace constructed for the purpose, the iron will imbibe an atomic quantity of carbon, and become Steel. This process is called _cementation_, and steel so made can be melted as readily as cast iron. Thus it will be seen that both cast iron and steel are combinations of iron and carbon, and in the same proportions, but not in the same state of combination. In cast iron, the carbon and iron are a mere _mechanical combination_, while in steel the iron and carbon are combined _chemically_.--Wrought iron, when pure, is free from carbon, and its ductility, toughness, &c., are due to the absence of carbon, sulphur, phosphorus, and other substances, with which it is occasionally pervaded. The French chemists are experimenting, and occasionally succeeding by accident, in causing heated iron to take the carbon from carbonic acid and other gases containing carbon, and thus becoming steel more rapidly, and at less cost, than when made by the process of cementation. Mr. Dixon, of Jersey City, has succeeded in making steel direct from the Adirondack iron ore, while Peter Cooper, Esq., Mr. Dickinson, and others, are manufacturing wrought iron direct from the iron ores of New-Jersey without first forming the pig or cast iron, and of course at less expense, as the saving of fuel is very great.