Density of mixed alkali silicate glasses

Density data of different mixed alkali silicate glasses have been analysed to determine the volume of the structural units in glass. It is deduced that the structural unit volume is not affected by the presence of another type of alkali oxide. The volumes obtained are the same as found for the corresponding binary alkali silicate glasses The molar volume changes linearly when increasing the concentration of an alkali oxide at the expense of the other. The rate of change is proportional to the difference in volume of the structural units that replace each other.