Abstract: A method of controlling the separation of coal from a mixture of coal and refuse in a froth flotation device by measuring the differential back pressure between two gas bubbler tubes immersed to different depths into the body of pulp in the device to produce a first control signal representative of the pulp density, and adjusting the rate of addition of a froth enhancement additive to the froth flotation device responsive to changes in said first signal; a second signal, produced by measuring back pressure of a single bubbler tube and representative of the pulp level in said device, can be corrected for changes in density by combining it with said first signal and then utilized to control liquid level in the cell by adjusting the rate of withdrawal of refuse therefrom.

Abstract: A high temperature pressure gauge comprising a pressure gauge positioned in fluid communication with one end of a conduit which has a diaphragm mounted in its other end. The conduit is filled with a low melting metal alloy above the diaphragm for a portion of its length with a high temperature fluid being positioned in the remaining length of the conduit and in the pressure gauge.