II.-British Glass-Sands:Part 1.

JSGT 1917 V01 T027-T061

IN the manufacture of the best types of glass it is essential that each of the batch materials should be as free from iron compounds as possible, in order to ensure the production of a colourless glass.
Present-day manufacturing methods have reached so high a pitch of perfection that it can safely be said that batch materials which have to be manufactured can be obtained practically free from
iron. For example, such substances as sodium carbonate, potassium carbonate, potassium nitrate. red lead oxide, borax, precipitated calcium carbonate, all of which are manufactured in bulk for the glass maker, show IittIe or no trace of iron impurity. Unfortunately, this cannot be said of any batch material which is
used in its native mineral form, e.g. sand, limestone. felspar, kaolin, ground quartz.