Determination of reducing components in glassmaking raw materials Report of the International Commission on Glass Technical Committee 2 "Chemical Durability and Analysis"

Abstract

A procedure bas been developed in Technical Committee 2 of the International Commission on Glass, which allows to determine the reducing strength (≙ chemical oxygen demand) of components accompanying glassmaking raw materials and possibly resulting in unwanted colouration of the glass. The procedure is comparadvely simple, but needs great attention in adjusting the reaction temperature of (148 ± 1) °C in the boiling (decomposition) vessel. This is achieved by a mixing of accurate valumes of the acids and water and monitoring the temperature of the boiling mixture. Furthermore, the mixture may have to be altered in pre-tests according to the prevailing atmosphere. The chemical oxygen demand for a feldspar gave, in an international round robin of 9 laboratories, a mean value of 1.72 mg O2/g of sample, with a coefficient of variance of only 7.6, and a coefficient of reproducibility of 0.13.