Ethylene Glycol and Ethanol Baths
Temperatures between approximately -78 °C and - 17 °C can be maintained by placing dry ice into a mixture of ethylene glycol and ethanol. The bath's temperature can be set by varying the relative amounts of ethylene glycol and ethanol. Dry ice sublimes at -78 °C.
If a bath is made with only ethanol, then it will maintain -78 °C until all the dry ice has sublimed. The bath will not freeze because ethanol's freezing point is -114 °C.
In addition, a cooling bath can be made with both ethanol and ethylene glycol. Since ethylene glycol freezes at −12.9 °C, then the "freezing point" of this mixture will increase to above -78 °C. Instead of freezing solid, however, the solution becomes thicker and gel-like once the dry ice has performed enough cooling. If a 60/40 mixture of ethylene glycol/ethanol is used, then a thick gel will form around the dry ice pieces around -60 °C, helping to maintain the temperature at approximately -60 °C.
Relative to traditional cooling baths, ethylene glycol mixtures have the advantage of never freezing solid. In addition, the solvents necessary are cheaper and less toxic than those used in traditional baths.
Read more about this topic: Cooling Bath
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