The thermal behaviour of potassium and sodium silicates

A few types of glasses have been investigated in this way. They were composed either of Na O and Si02 or of K20 and Si02. Their composition is given in Table VIII. 

Composition of glass Weight percentage of Molecular percentage of  

The density of these glasses was determined after thermal treatment at different temperatures. The values of these densities for the different glasses are reported in Tables IX, X, XI and XII. The density values of the glasses have also been plotted as a function of the temperature of treatment in Figs. 67, 68, 69 and 70. 

It appears that relatively low temperatures of treatment do not lead to a change in the density measured at 20°C. For the types of glass tested, from a certain temperature between 400°C and 450°C onwards there is a sharp fall in the density value until a temperature between 500°C and 65o°C is reached. Beyond this temperature no further change takes place in the density value. 

In Tables IX to XI the values of the refractive index, w2, for a number of temperatures of treatment are also given. The specific refraction defined according to 

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