136. The gauge glass on a coil-type auxiliary boiler is connected to the __________.

The gauge glass on a coil-type auxiliary boiler is connected to the accumulator, which contains the water and steam requiring level monitoring. The accumulator functions similarly to a steam drum, providing a steam space and water reserve. Gauge glasses indicate water level in closed vessels with both water and steam; the coils are a flow path, and other options are external components.