Just how and when the cementation process for making steel, to be now described, was discovered is not known. It may have been the result of the non-uniform working of the larger blast furnaces which were developing in Continental Europe during the Thirteenth century. From the German “natural steel” which was probably the steely product too rich in carbon for the wrought iron which they intended to make and much too poor in carbon to be the fluid cast iron which with the growing height and heat of the blast furnace they later did make, may have come the idea. More likely, a piece of thin wrought iron was accidentally left imbedded in glowing charcoal until it had absorbed some carbon. [Illustration: A CRUCIBLE MELTING ROOM. “MELTING HOLES” ARE BENEATH THE SQUARE COVERS ON THE FLOOR AT THE LEFT. NOTE THE NEW CRUCIBLES DRYING ON THE SHELVES, AND THE INGOT MOLDS AT THE RIGHT ] The first mention of cementation steel appears to have been by an Italian metallurgist, Vannuccio Biringuccio, who, in 1540, described the making of steel by heating billets of soft iron for a long time in molten cast iron. The modern method, the heating of wrought iron in powdered charcoal, was certainly known in the sixteenth century and this method of cementation has been practiced in France, England, Belgium and Germany since the seventeenth century. [Illustration: A SHEFFIELD (ENGLAND) CEMENTATION FURNACE ] Reaumur, the Frenchman, whose process of making cast iron soft by annealing bears his name and is still used in Europe, was the first to study and understand to any extent the cementation process. Publication, about 1722, of his complete directions for cementing iron gave great impetus to the manufacture of steel by this process. Fate, however, was unkind and his own nation, France, by reason of her small production of suitable iron for the work, was unable to profit greatly through his discoveries. Sweden, England and Germany were benefited to a much greater extent. During the early years many were the secret and wonderful mixtures and compounds offered for this work, but of them all carbon in some form was the only necessary element. Finely divided or powdered charcoal or bone dust has been mostly used. [Illustration: HUNTSMAN CRUCIBLE FURNACE—ORIGINAL TYPE ] [Illustration: ONE TYPE OF OIL-FIRED CRUCIBLE FURNACE ] Sheffield, England, steel makers, have been very successful in the manufacture of cementation steel. Their usual method is to pack flat strips of best Swedish Walloon iron in charcoal in rectangular stone boxes about four feet wide, three feet high and fourteen feet long. Alternate layers of small-sized charcoal and thin iron bars are piled in these boxes until they are filled, the bars not being allowed to touch one another. When full, top slabs are luted on to the boxes to make them airtight.