Choose simple distillation when you want the solvent back from a solution — not just the dissolved solid. Boiling sea water and condensing the steam gives water that is safe to drink; this is desalination. It works because water boils at 100 °C while the salt would need well over 1000 °C — a huge boiling-point gap.
Boiling chips are small pieces of rough, unreactive material. Their surfaces give vapour bubbles easy places to form, so the liquid boils gently and steadily. Without them the flask can bump — big bubbles burst out violently and can throw hot liquid up the neck and into the condenser, spoiling the distillate.
The rubber bung seals the neck so no vapour escapes into the room — it goes in first. The thermometer then slides through the hole in the bung until its bulb sits level with the mouth of the exit side arm. That way it measures the temperature of the vapour actually leaving the flask, not the liquid underneath. A bulb set too high reads the cool air above; set too low it reads the boiling liquid — both give the wrong temperature. While pure water is distilling over, a correctly placed thermometer holds steady at 100 °C.
Turn the collar to close the air-hole first, then strike the sparkler at the top of the barrel. The gas lights with a yellow, wavy luminous flame — easy to see and safe, but cool and sooty. Now open the air-hole: air mixes with the gas and the flame turns blue and roaring — the non-luminous flame. It is much hotter and clean, so it is the flame you heat with.
Cooling water enters the condenser jacket at the bottom and leaves at the top — flowing in the opposite direction to the vapour. This counter-current arrangement keeps the jacket completely full and cold along its whole length, so the vapour meets colder and colder glass and condenses fully into liquid, dripping from the condenser's downturned mouth into the receiver below.
The condensed liquid dripping into the receiver is the distillate: here, pure water. The salt is the solute — it cannot evaporate at these temperatures, so it stays in the flask and appears as a white solid as the water level falls.
| Evaporation to dryness | Simple distillation | |
|---|---|---|
| What is kept | Only the solid solute | The pure solvent (the distillate) and the solid left in the flask |
| What is lost | All of the solvent escapes as vapour | Almost nothing |