Page:Popular Science Monthly Volume 39.djvu/753

Rh on removal to be very crystalline and brittle. These changes of structure and fracture were due to the absorption of carbon from the charcoal dust in which the bars had been packed.

Fig. 50 is a cross-section of a "cementation" or "blister-steel" "converting furnace" in which the various parts are so plainly designated that additional description is unnecessary. The degree of carburization, and consequently the hardness of the steel produced in such a furnace, necessarily varied, and for the convenience of manufacture and trade the product was assorted into six grades or "heats."

When steel was wanted of closer grain, firmer texture, and more reliable character, a certain number of bars of this "blister steel" were made into a bundle or "fagot" and welded together, and the resulting bar was called "single shear" steel; and if a still higher quality was required, bars of "single shear" were welded and drawn into bars called "double shear steel."

Previous to the year 1812 we have no record of there having been any steel produced in America by other than the processes already described, but in that year John Parkins and his son, Englishmen, "are said to have made an unsuccessful attempt to make cast steel in New York City," and the same authority tells us that they were employed, in 1818, at Valley Forge, Pa., to make cast steel for a saw manufactory.

In 1831 John R. Coates, of Philadelphia, stated that there were then in the United States fourteen blister-steel furnaces, which had "a capacity sufficient to supply more than sixteen hundred tons of