Thermal-expansion characteristics of some ground-coat enamel frits

Thermal-expansion determinations were made on 11 sheet-iron ground-coat frits of the single-frit type, using the interferometer and also a quartz-tube dialindicator apparatus. "Critical" temperatures for both heating and cooling were determined. Mean coefficients of expansion from 25 to 400 C, and total contraction from the critical temperatures to 25 C during cooling were correlated with variations in composition. Total differential contractions between enamelingtype iron and the frits were also computed and correlated with variations in composition. Constants were determined which, when substituted in simple firstorder equations, permit the computation of the expansivity of each frit at any temperature or temperature interval between 25 C and the critical temperatur es.