After the pattern of Buss (Glas techn. Ber., 30, 145 (1959)) a simple high temperature microscope was constructed, which, although with low magnification, was possible to follow after the glass melting process up to about 1450°C by continuous observation.
As the equipment has proved to be useful for present purpose a series of studies was made on the effect of the minor ingradients upon the melting process Na₂O-CaO-MgO-SiO₂ glass by observing the evolution of bubbles, change of the fluidity as well as the velocity of dissolution of quartz grains.
The comparative test of 12 additional agents was carried out with a result showing that CaF₂, Li₂CO₃ and H₃BO₃ were effective in the case of the maximum holding temperature of 1400°C.