The Visual Spectrophotometry of Glasses, with Reference to Low Absorptive Glasses

JSGT 1942 V26 T254-T271

The types of spectrophotometer designed primarily for the measurement of the light absorption of homogeneous glass are generally not suitable, without modification, for the measurement of low absorption, especially in the case of glasses in which cords and strain are markedly present. A simple analysis shows that when using a small-sized source of illumination, such as the Pointolite lamp, the thickness of the specimen may have to be limited to 0.7cm. On the other hand, if a broad uniform diffusing source is available, specimens up to 13cm thick can be studied without causing serious error. By this means, specimens in the form of rods and sheets can be studied by allowing the illuminating rays to be reflected internally. An apparatus constructed on this principle is described and typical results are recorded. Its application to problems of low absorption, such as occur in the processes of decolourising glasses, is discussed. The possibility of using comparatively thick glass specimens with Hardy's recording spectrophotometer is pointed out.

T. H. Wang, M.Sc., D.I.C