Phosphorus is sometimes employed for giving soundness to the castings, being added to the bath in small quantities in the form of phosphor-copper containing about 10 per cent. of the non-metal. Although very little of this phosphorus is retained by the metal, being mostly eliminated as oxide, special caution is required in employing it for high-grade conductivity copper, since the effect of very small quantities has a deleterious influence upon the conducting properties. Silicon also is used for a similar purpose, and causes a considerable increase in toughness. (_f_) When intended for conductivity work, the metal is cast into the form of “wire-bars” of very varied shape and size, according to requirements; thus the 100-lb. bars are about 3 feet long by about 3 inches square section, the 500-lb. bars 7 feet long by about 4½ inches square. Furnace samples weighing about 1 lb. are drawn down gradually to about ⅛-inch wire, and are tested for conductivity, as well as for strength and toughness, occasional analysis being also undertaken, whilst samples of the wire-bars in market form are similarly examined. [Illustration: _a b_ Fig. 76.—Microstructure of Commercial Copper containing Oxygen (Hofman). _a._ Calumet and Hecla copper after 60 minutes’ poling. 0·22 per cent. oxygen = 1·98 per cent. Cu_{2}O. _b._ Calumet and Hecla “dry” copper before poling. 0·64 per cent. oxygen = 5·76 per cent. Cu_{2}O. Compare with Fig. 6, p. 28. (_By permission of American Institution of Mining Engineers._)] References. Ulke, T., “Modern Electrolytic Copper Refining.” (With complete Bibliography). Peters, E. D., “Modern Copper Smelting” (1905). (Chapter xviii. by M. Barnett.). Mineral Industry. Annual Review. Cowper Coles, S., “An Electrolytic Process for the Production of Copper Wire.” _Proc. B’ham. Met. Soc._, 1908–9, p. 5. Schnabel and Louis, “Handbook of Metallurgy,” pp. 327–369. Wraith, W., “Sampling Copper Anodes at Anaconda.” _Trans. Amer. Inst. Min. Eng._, March, 1910. “The De Lamar Electro-Refinery at Chrome, New Jersey.” _Eng. and Min. Journ._, Jan. 13, 1906, p. 73. Flinn, F. B., “Electrolytic Copper.” _The Metal Industry_, April, 1910, p. 112, vol. ii., No. 3. Greenawalt, W. E., “The Greenawalt Electrolytic Process.” _Eng. and Min. Journ._, Nov. 26, 1910, p. 1062. See also References to Johnson (p. 34), Hofman and others (p. 50), Keller (pp. 50, 215), and Peters (p. 80). INDEX.