Abstract
WE are very pleased to be able to chronicle an application which Mr. Frederick Siemens has recently made in his regenerative gas radiating furnace, described in the autumn of last year (NATURE, vol. xxxi. p. 7). It consists in the production of glass which appears to be of a very homogeneous character and of considerable strength and hardness, and will doubtless become available for a number of useful purposes. The scientific principle which is applied in the three distinct processes to which we propose to refer shortly, is that of keeping the whole body of the glass at a uniform temperature during the operations of heating and cooling—that is to say, that at each unit of time the whole mass shall be at one temperature. Two methods have hitherto been employed by means of which glass has been rendered more or. less independent of variation of temperature. The oldest of these is that carried on in the annealing kiln, in which the manufactured articles of glass are allowed to cool very slowly. The more modern is that of De la Bastie; in this process the finished articles of glass had generally to be annealed in the first instance, then heated to such a temperature as to soften them, when they were immersed in a bath of heated oil maintained at a temperature above 300°C., which was said to make them tough. The objection to annealing is mainly that of cost, but the objection to the De la Bastie process is that it is wrong in principle, as, owing to the manner in which cooling is effected, the glass is in a state of tension throughout, which is brought to evidence by means of the polariscope. The glass produced by the processes to be described are almost free from internal strain, and Mr. Siemens holds that, could the principle he propounds be carried out perfectly in practice, the glass would be free from tension throughout its whole mass. A corollary which may apparently be drawn from this proposition is that every metal not cooled in the way proposed is in strain; but that, owing to the much greater tensile strength of metals, the state of tension does not become evident in the same manner as in glass, which is notably brittle.
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Tempered Glass . Nature 31, 413–414 (1885). https://doi.org/10.1038/031413b0
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DOI: https://doi.org/10.1038/031413b0