Melts weighing 45g of 16.5 Na2O, 10.0 CaO. 73.5 SiO2 (wt%) were made at 1450 deg C with and without antimony oxide and sodium nitrate as refining agents. Additions of antimony ranged from 0.012 to 1.2% Sb2O3 and sodium nitrate was used to supply 1.0 or 5.0% Na2O. Numbers of bubbles, bubble size distributions, composition of gas in bubbles, and the total and trivalent antimony contents of the glass were determined. Suitable proportions of antimony, the best being 0.3-0.6% Sb2Oe, together with 1.0% Na20 supplied as nitrate, gave good refining; larger proportions impaired refining. Only the number of bubbles and the composition of gas in the bubbles could be used to determine the best proportion of refining agent. The general pattern of behaviour with antimony was very similar to that given by arsenic even though antimony is much more reduced.
