The condenser is part of the distillation apparatus. Its top part is connected to the distilling flask and the thermometer by an adaptor and its bottom part leads to the collecting flask. The most common condenser has 2 hollow chambers. In the outer chamber, there is a constant flow of cold water, that cools the glass condenser. The water enters at the bottom part of the condenser and exits at the top part. As the hot vapor enters the inner chamber of the condenser, it's cooled down by the cold surface, condenses, and passes down the condenser into the collecting flask. This setup prevents the hottest vapor from contacting the coldest water, avoiding thermal shock to the glassware.

A diagram showing the process of ethanol distillation. The first section shows a 250 milliliter round bottom flask that contains 20% ethanol and 80% water. There is an arrow pointing to the second section that shows the flow of distillation and cool water in a distillation apparatus. The distillation process moves from left to right: The distilling flask is heated to 78 degrees celsius, then the hot vapor moves through the condenser, which cools it down, and then the distilled liquid is collected in the collecting flask. The flow of water goes in the opposite direction, entering at the bottom part of the condenser, closest to the collecting flask, moving towards the distilling flask, where it exits. There is an arrow point to the third section, showing a 100 milliliter round bottom flask containing 56 % ethanol and 44 % water. 
Figure 1: Process overview of ethanol distillation

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