This article takes an in-depth look at the effects of sulphates on the melting, working and other properties of potash lead glass. In some branches of glass manufacture, alkaline and other sulphates serve as raw materials. The use of saltcake (sodium sulphate) as the source wholly or partially of the alkaline constituent of window glass and bottle glass is well known, and its influence is a matter of fairly common knowledge. In cases where it is used unmixed with any reducing agent, it is apt to form a thick floating layer, only comparatively slowly decomposed by the furnace gases and by the sand, and under these conditions is a source of trouble by reason of its corrosive action on the furnace walls. Saltcake used in tank furnaces not only serves as a source of alkali but has undoubted advantages in other directions. Added to the extent of from 10-30% of the total alkali it tends, apparently, to assist fining operations, whilst it undoubtedly prevents the formation of the white scum, consisting mainly of silica, which is not infrequently seen on glass made wholly from soda ash. Moreover, practical experience shows that a glass produced from saltcake has working properties somewhat different from the one where soda ash alone is the source of alkali. It is reputed, for example, in the case of window glass, to give a more durable, stronger and more readily drawn glass when cylinders are made, whilst bottle blowers aver that saltcake glass is "sweeter" than soda ash glass.
