Bad soda-glass or that which has been kept for many years, tends to devitrify when worked. [Please select]
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The following qualities are desirable in a glass for ordinary working: (1) moderately low working temperature, (2) freedom from air bubbles, striations and irregularities, (3) proper composition, so that the glass will not devitrify or crystallize while being handled at its working temperature, (4) ability to withstand rapid heating without cracking. [Please select]
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Even good glass will begin to devitrify in this way if heated too long at the highest temperature of the flame, so care should always be taken (1) _to reduce the time of heating of any spot of glass to a minimum_; _i. [Please select]
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