Ultra-pure, virgin Saint-Gobain Chemware PTFE boiling stones promote gentle, efficient boiling and help prevent overheating, even of highly volatile liquids. Ideal for continuous extraction methods. Stones minimize "bumping" during reflux and distillation. The boiling stones are not affected by acids, hydrocarbons, ketones, esters, alcohols or alkalis. They are easily cleaned and non-contaminating. Shows no trace of face acidity or alkalinity. They will not scratch or abrade glassware and leave no residue. Usable up to 550°F (88°C).