The distilling flask is generally the largest round-bottomed flask and so houses your crude, unpurified mixture. It’s placed over a heating source that heats the mixture until the relevant components vaporize and leave the flask.
We can reduce the pressure in the distilling flask in order to heat the mixture more cost and time-effectively, however, this puts us at the risk of flash boiling the mixture. If the pressure inside the flask is significantly lower than the compound’s vapor pressure, then the compound can rapidly volatilize, especially when heated in the flask. We therefore can add small solids, packed with air, known as boiling chips, to prevent this.
Figure 1: Distilling flask containing boiling chips