Abstract
IT is known that the presence of a minute trace of gas in a metal may greatly change its properties. For example, the magnetic permeability of commercially pure iron is greatly increased by eliminating the small amount of gas which it contains. In the Bell Laboratories Record of September, E. E. Schumacher gives an interesting account of the methods employed to free metals from gases, particularly those used in the telephone industries. When the high degree of purity required for research purposes is desired, the metal is usually heated in a vacuum at a temperature above the melting point for a considerable time. But even at low pressures, sufficient gas may be left in the metal to be troublesome. When this occurs, alternately melting and partially solidifying the metal is employed in a high vacuum. In this way, almost complete elimination of the gas can be obtained. The metal to be freed of gas is placed in a shallow boat of fused aluminium oxide. This gives a large surface exposure and reduces the head of metal through which the gas must pass to escape. The apparatus is sealed in a pyrex glass tube connected to the pumping system. The tube is placed in a nichrome resistance furnace and a temperature of 450 ° C. is maintained until gas is no longer liberated. A high-frequency coil is then substituted for the nichrome furnace and the metal is melted by induced high-frequency current. It is possible to keep the metal at its melting temperature indefinitely without heating the pyrex glass tube to its melting point. The final pressure may be as low as one thousand millionth of an atmosphere. The comparison of the properties of the purified samples with those of samples of any given gas content is of great importance.
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Gases in Metals. Nature 132, 999 (1933). https://doi.org/10.1038/132999c0
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DOI: https://doi.org/10.1038/132999c0