A simplified and effective pressure cell together with an experimental procedure has been developed and applied to compress samples of SCHOTT N-BK7((R)) glass under static high pressures in a piston-cylinder apparatus. Results from the density and volume recovery measurements show that, the glass samples were effectively densified in piston-cylinder apparatus with the density at room temperature increasing linearly with frozen-in pressure. To explain the experimental data, we developed a mathematical model based on a suggestion by Gupta (1988) with two internal parameters, named fictive temperature (T-f) and fictive pressure (P-f), which fits the experimental data well.