In a flask containing dry air and some liquid silicon tetrachloride, $\mathrm{SiCl}_{4}$, the total pressure was 988 torr at $225^{\circ} \mathrm{C}$. Halving the volume of the flask increased the pressure to 1742 torr at constant temperature. What is the vapor pressure of $\mathrm{SiCl}_{4}$ in this flask at $225^{\circ} \mathrm{C}$ ?