Observation of a good blacksmith at work and a few minutes’ conversation with him about his “art” will give one greater knowledge and appreciation of the carbon tool steels than volumes of writings concerning them. Along with it will come more respect for the skill of these clever men whose handiwork is never exhibited in salons and about whom the world hears little, though indebted to them for a great measure of its civilization and prosperity. [Illustration: HIGH CARBON TOOL STEEL IS EXTREMELY BRITTLE WHEN HARDENED AND HAS VERY LITTLE MALLEABILITY WHEN ANNEALED ] What and how much would be possible without machines and proper tools? [Illustration: QUARTER-INCH MILD STEEL PLATE WITH DOUBLE FOLD. FOLDED COLD WITHOUT SLIGHTEST CRACK ] About sixty years ago steels of much lower carbon content appeared. They have been made softer and softer until we have what we now know as the “mild” steels and even the almost or practically carbonless material which we called “open-hearth iron” or “ingot iron” in a former chapter. These have not the hardening property but they possess softness, ductility and freedom from brittleness which the higher carbon steels always lack. For such real evidences of our Twentieth Century civilization as the great bridges, ships, buildings, etc., they are indispensable, for they are easily cut, bent and otherwise worked into shape, and they combine pliability with sufficient strength for the service intended. Such steels are desirable, for when overloaded they bend before they break, thus giving warning of the danger. These mild and medium steels are of immense importance industrially. Of the 31,000,000 tons of steel made in the United States during 1912 probably 99 per cent was of the soft and medium varieties. It has been said that “the exception proves the rule.” Cementation steel is the exception to the rule which we gave in Chapter VI that steel is always melted during its manufacture. If a thin piece of bar iron be packed in powdered charcoal and heated at low red heat for some time, the metal, after cooling, will be found to have acquired the hardening property. In other words by _absorption of carbon_ it will have become steel with all of the characteristics of that material. Neither the iron nor the carbon by which it was surrounded have melted, yet in some way carbon has penetrated into the iron and if the heating has been sufficiently long, carbon will be found at the center of the bar. But _always_ there will be more carbon in the outer layers of the bar than in those farther inside, i. e., it will be found in diminishing amounts as we approach the center. [Illustration: SHELBY SEAMLESS STEEL TUBING CRUSHED ENDWISE ]