4. A large closed cylindrical tank 4 m high with its bottom on a level ground contains two layers of liquid. The bottom layer is water 2 m deep. The top layer is occupied by a liquid whose specific gravity is not known, to a depth of 1 meter. The air space at the top is pressurized to 16 kPa above atmosphere. A 50 mm orifice with a coefficient of velocity of 0.98 is situated 1 m from the bottom of the tank. The jet from the orifice hits the ground 3.5 m horizontally away from the vena contracta. Determine the specific gravity of the liquid at the top layer.