Total Carbon in Coal Determined by Analysis of Gas from Bomb Calorimeter

Abstract

perience to sharpen properly and keep the knife in condition. These considerations have led the present writers to publish the result of a study of the polishing methods that has been in progress for some time, and in which has been developed a technic that is rapid, can be successfully carried out with any polishing equipment, and leads to the formation of ideal surfaces for microscopical examination.Figures 11, 12, 13, and 14 illustrate the appearance of the structures of a 1 per cent antimony-lead alloy after various treatments, as developed by the methods of polishing and etching described here. Figures 15 and 16 illustrate the structure of a 3 per cent tin-lead alloy as developed by the same process.The time required to prepare a sample depends entirely on the skill of the operator, an experienced one being able to complete the entire operation in less than an hour. The structure of properly prepared samples can be easily developed in 10 seconds, even when employing as slow an acting reagent as that previously described. It is by no means necessary to etch deeply in order to get below polishing imperfections.The fact that the blackening often observed during the polishing operation can be avoided by careful manipulation or removed, when it appears, by gentle polishing on a very wet cloth, seems to indicate that its cause is other than oxidation due to the polishing operation. It has been observed that a polished specimen of lead will retain its bright surface for several days.