Iron foil specimens were anodically polarized by means of a potentiostat in 1N H2SO4 , 0.1N normalNaOH , and a sodium borate‐boric acid solution (pH, 8.5). Both passive, active, and transpassive regions of the polarization curve were studied for each solution. The oxide films were examined while still in contact with the iron foil by selected area transmission electron diffraction. Five iron planes were studied: {100}, {110}, {111}, {210}, and {211}, and the epitaxial relationship of the oxide to the iron substrate determined. Evidence was found indicating that in all of the electrolytes used the passive film contained γ‐Fe2O3 , while the nonpassive films did not.

Alloys in the iron-chromium-molybde num-nickcl syste m were examined after qu enching from 2,200°, 2,000°, 1,800°, 1,650°, and 1,500° F. Composit ional l imi ts of s tability of se ven phases were summarized in diagram s. F e, Mo was foun d. to be a stable phase; and a ternary phase, not previou sly r eported, was identifi ed to hav e the approximate composition of 4 p ercen t of chromium, 53 p ercent of iron, and 43 p er ce nt of molybdenum.

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Electrodeposited lead dendrites were grown and examined by x-ray diffraction and metallographically. Their structure was essentially that of two crystals having a twist relation about a common [111] pole which was normal to the flat surface of the two-dimensional dendrites. Each dendrite contained many small voids or channels. The direction of growth was either about halfway between a <211> direction of one crystal and a neighboring <211> direction of the second crystal or halfway between <110> directions.Electrodeposited dendrites 2 have been described and reviewed extensively by Wranglen (1). He examined dendrites of lead, tin, silver, cadmium, and copper microscopically and by x-ray diffraction and described them as single crystals. Faust and Johns (2) examined electrodeposited dendrites of lead, silver, copper, gold, and aluminum, and by metallography found at least one grain boundary in each of the dendrites growing in <211> or direction.The lead dendrites, as shown by Wranglen, are of two main types: those that are flat and growing in a direction and those that are three dimensional and growing in a <100> direction. The growth of dendrites is favored by conditions of solution depletion, and they are branched at right angles. The dendrites have been described as monocrystalline, branched at 60 ~ , and growing with the plane of the dendrite parallel to a {lll} plane. The lead dendrites examined by Faust and Johns were of the <110> type with "twin planes."As part of a program of investigating the growth and character of metal crystals grown by electrodeposition, we had occasion to grow and examine some lead dendrites. We had hoped to use these as seeds for growing larger crystals, and we wished to know something about the quality of the crystals. Wranglen had considered only morphology and x-ray diffractometer measurements, and Faust and Johns had made only a very limited metallographic examination. All in all very little was known about the lead dendrites which are extremely easy to grow.We grew numerous dendrites of lead by electrodeposition. In many respects they appeared to be the <110> dendrites of Wrang]en, but were neither twinned in the usual sense nor single crystals. The apparent difference is probably attributable to the use of more powerful tools for their examination. Certainly these were not unusual growths inasmuch as they were obtained consistently and to the virtual exclusion of other types. Growth of DendritesThe dendrites were grown by electrodeposition in a 0.5M solution of lead acetate and 2M ammonium acetate with a lead anode and cathode. Reagent grade chemicals and distilled water were used without any purification steps.The plating cell consisted of a 100 ml beaker filled with electrolyte and covered with a rubber stopper. The lead anode was supported at one side of the beaker through a hole in the stopper. On the other side, a glass tube 4 mm in diameter, was inserted in a hole in the stopper and positioned so...

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