Excerpt from Metallographic Polishing, Vol. 1: Automatic Metallographic Polishing Machine The number of polishing powders is also very great, among them being the oxides of iron, chromium, tin, zinc, manganese, aluminum, and magnesium. From the standpoint of cleanliness the last two, which are white powders, appear to be the most convenient. Tin oxide 18 also a white powder. Glazebrook2 states that putty powder (snoz) was at one time extensively used as a polishing powder, but has been discarded for reasons of health._ Magnesium oxide appears to be the most uniformly fine powder available. An objection to its use is its tendency to harden on exposure to air. The usual grade of levigated alumina contains traces of alkali, which are objectionable for polish ing aluminum and its alloys, because the surface becomes tarnished. Alkali-free alumina of a fineness equal to magnesia would be preferable to the latter because _of the tendency of magnesia to harden. A microtome is available in this laboratory, and the question of the preliminary preparation of a plane surface of soft metals by means of this instrument will receive attention. An interesting proposal for preparing specimens with a cutting tool is that of turning with a diamond. This has been tried by the Bausch Lomb Co and may, perhaps, be considered further. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.