Cooling bath
A cooling bath or ice bath, in laboratory chemistry practice, is a liquid mixture which is used to maintain low temperatures, typically between 13 °C and −196 °C. These low temperatures are used to collect liquids after distillation, to remove solvents using a rotary evaporator, or to perform a chemical reaction below room temperature (see Kinetic control).
Cooling baths are generally one of two types: (a) a cold fluid (particularly liquid nitrogen, water, or even air) — but most commonly the term refers to (b) a mixture of 3 components: (1) a cooling agent (such as dry ice or ice); (2) a liquid "carrier" (such as liquid water, ethylene glycol, acetone, etc.), which transfers heat between the bath and the vessel; (3) an additive to depress the melting point of the solid/liquid system.
A familiar example of this is the use of an ice/rock-salt mixture to freeze ice cream. Adding salt lowers the freezing temperature of water, lowering the minimum temperature attainable with only ice.
| % Glycol in EtOH | Temp (°C) | % H2O in MeOH | Temp (°C) |
|---|---|---|---|
| 0% | −78 | 0% | −97.6 |
| 10% | −76 | 14% | −128 |
| 20% | −72 | 20% | N/A |
| 30% | −66 | 30% | −72 |
| 40% | −60 | 40% | −64 |
| 50% | −52 | 50% | −47 |
| 60% | −41 | 60% | −36 |
| 70% | −32 | 70% | −20 |
| 80% | −28 | 80% | −12.5 |
| 90% | −21 | 90% | −5.5 |
| 100% | −17 | 100% | 0 |