The Density of Silicate Glasses as a Function of Composition*

The volume per gram atom of oxygen in a well-annealed silicate glass is given quite accurately by the equation VO=k+bSi+cSiNSi+∑cMNM, where k is a very small constant characteristic of the annealing technique, NSi and NM are the numbers of Si or other "metal" atoms per atom of oxygen, bSi and cSi are constants which are different for different ranges of NSi values, and cM are constants valid (insofar as can be determined from present data) for all values of NM. For boron-containing glasses separate terms are required for tetrahedrally surrounded and for triangularly surrounded atoms, the relative numbers of which depend on the relative amounts of Si, B and O. With the aid of the above equation, one can calculate densities from compositions simply and quite accurately. The empirical results obtained are interpreted theoretically.