C &EN’s article about a refrigerated condenser for rotary evaporators, or rotovaps, describes a useful alternative approach for reducing the use of laboratory dry ice and tap water (Feb. 1, page 22). In a subsequent letter to the editor (C&EN, March 14, page 4), Richard Kjonaas mentions the use of ice as a practical and cheap alternative.
My lab mates and I have also used ice for cooling rotovaps equipped with cold fingers with great efficiency for several years. What’s more, we have found that the addition of sodium chloride (common salt) to the ice improves the cooling efficiency significantly for our use. We have thus routinely been able to remove higher-boiling solvents such as ethyl acetate and cyclohexane at a water bath temperature of 35–40 °C when using the laboratory water aspirator vacuum.