Dimensional changes caused in glass by heating cycles

In obtaining expansivity curves for a medium flint glass, samples of the glass were tested which had previously received one or another of several different heat treatments, and in these tests heating cycles were employed which made it possible to determine the magnitude of the so-called "permanent" changes in length which are caused either by the annealing or the "disannealing" which may result from the heat treatment imposed on the glass by the heating cycle employed.Annealing decreases the length and specific volume, while disannealing increases them.It is show r n that these effects are related to certain icepoint shifts observed in thermometers, and to other effects sometimes observed in various types of glassware.CONTENTS Page I. Introduction 627 II.Experimental methods and apparatus 631 1.General character of the glass tested ^631 2. Heat treatment of samples 634 3. Preparation of test specimens 634 4. The furnace 635 5.The temperature measurements 635 6.The measurement of fringe displacements 636 7. The heating cycles 637 III.Experimental results 637 IV.Concluding discussion 644