โ Scribed by C.G. Peters; C.H. Cragoe
No coin nor oath required. For personal study only.
THE methods and results of an investigation of the thermal expansion and the chemical composition of different kinds of optical glass? chemical glassware, and commercial tubing are presented in this paper.. A ring of the glass, placed between two fused quartz plates, was heated in an electric furnace and its expansion measured by the Fizeau interference method. Observations were made in the temperature regions between 20' a.nd 650' C. on thirty-two different kinds of glass. Their dimensional changes are represented by curves which show that the glass passes through a critical expansion region, in which the expansion rate increases by two to seven times.
This critical region, which for any one glass does not exceed 4o", was found as low as 400' C. with one glass and as high as 575" C. with another. About 75" above the critical region the glas's softens and contracts.
A comparison of results shows that the heat absorption observed by Tool and Valasek occurs in the same temperature region as the critical change in the expansion.
From these determinations of the dimensional changes of glass, the followin g information is obtained: the thermal expansion above and below the critical temperature, the temperature for most careful and thorough annealing, the upper limit for rapid annealing, and the region where careful cooling is essential. RECOMMENDED SPECIFICATIONS FOR GREEN PAINT-SEMI-PASTE AND READY MIXED.
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