Ultra-pure, virgin PTFE chips promote gentle, efficient boiling and help prevent overheating–even of highly volatile liquids. 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 (288°C). Ideal for continuous extraction methods.