Thermometer Placement in the Y-Adaptor

The bulb part of the thermometer is positioned near the side arm of the Y-adaptor so that it monitors the temperature of the vapors. See the illustrations below. If it is too low, it will be too close to the boiling liquid and will read higher than the true vapor temperature. If it is positioned too high, it will be out of the path of the vapors and read lower than the true temperature.