1. equal to atmospheric pressure (barometric reading)
2. After the low boiling liquid is completely distilled over, the residual liquid has a temperature only slightly higher than the low boiling liquid, not enough to vaporize the high boiling component. At that time there is no vapor at the thermometer and the reading drops.
3. Drop in barometric pressure lowers the boiling point, increase in barometric pressure shifts the boiling point upwards.
He can heat the column with a heating mantle to 65 °C.