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It is important to add boiling stones before heating begins, since a liquid may froth violently and boil over if they are added when the liquid is hot. Although it may be spectacular as the solvent shoots out the top of the condenser, it is dangerous, and also annoying to have to set up your reaction again. Always add one or two new boiling stones to a cooling liquid before reheating. This is because liquid is drawn into the pores of a boiling stone when boiling stops, making the stone less efficient.

Narrative

First remove your condenser carefully, and place it on the bench. Add some boiling stones to the round-bottomed flask. If you must add a solid reagent it is transferred to the flask using a powder funnel or folded piece of paper.