[18] James M. Swank, _History of the manufacture of iron in all ages_..., Philadelphia, 1892, pp. 390, 393.
[19] _Country Gentleman_, 1857, vol. 10, p. 129.
[20] Reports on spark test by E. A. Battison, U. S. National Museum, and on metallurgical investigation by A. H. Valentine, Metallographic Laboratory of the Bethlehem Steel Company's Sparrows Point Plant.
[21] For this information I am indebted to Mr. E. A. Battison of the U.
S. National Museum staff.
[22] Abraham Rees, _The cyclopaedia; or universal dictionary of arts, sciences, and literature_, Philadelphia, 1810-1842, vol. 33, under saw.