. Metallographic etching reagents: I, for copper. f copper in different directionsis the fundamental reason for the difference in etching character-istics. The influence of oxidizing agents in increasing the rateof solution of metals by acids has been described by Watts andWhipple.^ The increase in the loss of weight of specimensimmersed in the various mixtures of acid and oxidizers was usedas a measure of the influence of the oxidizer. The results obtainedwere of the same character as those described here. V. TYPICAL ETCHING REAGENTS AND RESULTS OBTAINED Below are given micrographs of copper
. Metallographic etching reagents: I, for copper. f copper in different directionsis the fundamental reason for the difference in etching character-istics. The influence of oxidizing agents in increasing the rateof solution of metals by acids has been described by Watts andWhipple.^ The increase in the loss of weight of specimensimmersed in the various mixtures of acid and oxidizers was usedas a measure of the influence of the oxidizer. The results obtainedwere of the same character as those described here. V. TYPICAL ETCHING REAGENTS AND RESULTS OBTAINED Below are given micrographs of copper of the five types used,showing the behavior of various etching reagents upon copper toillustrate the principles discussed in the foregoing sections (, inclusive). In Table i below, the corapositions of thevarious solutions as well as information concerning the etching SQ. P. Watts and N. D. Whipple, Corrosion of Metals by Acids, Trans. Am. Electrochem Soc, 32,p. 257, 1917. RawdonlLorentz J Metallographic Etching Reagents for Copper 657. iiW9£i^^3mm Fig. 9.—The characteristic selective oxidation of different crystalsduring the contrast-etching of hot-rolled copper with an ammo-niacal oxidizing solution. \ioo The specimen was repeatedly etched with a mixture of concentrated ammoniumhydroxide and hydrogen peroxide (1-20), the fikn of oxide which coveredcertain of the crystals being removed with concentrated ammonium hydroxidebefore each new etching. The same crystals are always darkened by theetching, it is not a matter of chance. In the two micrographs, a and h, thesame crystals are darkened in the later stage, b, as in the earlier one, a 658 Scientific Papers of the Bureau of Standards [Vol. i6 are given. The solutions listed in the table are intended as typesillustrative of the principles given in the foregoing sections ratherthan a complete reference table in any sense of the word. TABLE 1.—Typical Etching Reagents for Copper No. Type Composition a Approximateet
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