MERCURY GAS GOVERNOR
In a governor of this style, the gas from the main line passes through the upper pipe, down through the internal tube, and escapes between the end of this tube and a column of mercury in the mercury tube, passing up behind the internal tube, and out through the lower pipe to the burners.
To prepare the governor for use, remove the adjusting rod and pour in mercury until it rises in the mercury tube almost to the lower end of the internal tube, which can be seen through the glass disk at the side of the governor. When the metal in the pot reaches the proper temperature, the surface of the mercury stands at the lower end of the internal tube, but a notch in the side of this tube above the mercury permits a flow of gas sufficient to prevent shutting the gas entirely off underneath the pot. When the temperature falls, the mercury in the holder and column will be cooled, and its surface lowered in the tube. This will allow an increased flow of gas to the burner until the temperature of the pot is raised to the proper point.
The regulation of the governor is effected by moving the adjusting rod in or out. If the temperature in the pot is too high and the mercury fails to close the tube, the adjusting rod must be moved in until the mercury raises in the tube. If the temperature in the pot is too low, the mercury closes the tube before the proper temperature is reached in the pot. Thus the rod must be moved out until the mercury is lowered from the top of the tube to the proper extent.