Heating devices sand bath

If the reaction does not require elevated temperatures, but needs only to be stirred, the system can be assembled without the heat-transfer device (sand bath or metal plate). Some stirred reactions, on the other hand, require cooling. 

The most common heating devices are heating tapes and mantles and sand, water, steam, wax, silicone oil, and air (or nitrogen) baths. These should be used in such a way that if an explosion were to occur the heating medium would be contained. Heating baths should consist of nonflammable materials. All controls for heating and stirring equipment should be operable from outside the shielded area. (See Chapter 6, section 6.C.5, for further information.)... 

Perhaps the most common types of electrical equipment found in a laboratory are the devices used to supply the heat needed to effect a reaction or a separation. These include ovens, hot plates, heating mantles and tapes, oil baths, salt baths, sand baths, air baths, hot-tube furnaces, hot-air guns, and microwave ovens. The use of steam-heated devices rather than electrically heated devices is generally preferred whenever temperatures of 100 °C or less are required. Because they do not present shock or spark risks, they can be left unattended with assurance that their temperature will never exceed 100 °C. 

The temperature during the distillation may be monitored either with a thermometer or a stainless steel temperature probe. If a stainless steel probe is used, it must be used in conjunction with either a digital thermometer or one of the Vernier devices (see Technique 13, Section 13.4 and Technique 14, Figure 14.12). Your instructor will provide instructions about the method that you will use. Insert the thermometer (or probe) so that the bulb is level with or slightly below the cap connecting the Hickman head to the air condenser. Also use a thermometer to monitor the temperature of the heat source. Cover the top of the sand bath (if used) with a square of aluminum foil with a tear from the center of one edge to the middle. 

The methods described previously may be used over a range of about 50°C to over 200°C. A hot water bath, however, may be a suitable alternative for temperatures below 80°C. A beaker (250 mL or 400 mL) is partially filled with water and heated on a hot plate. A thermometer is clamped into position in the water bath. You may need to cover the water bath with aluminum foil to prevent evaporation, especially at higher temperatures. The water bath is illustrated in Figure 6.6. A mixture can be stirred with a magnetic spin vane (Technique 7, Section 7.3). A hot water bath has some advantage over an aluminum block or a sand bath in that the temperature in the bath is uniform. In addition, it is sometimes easier to establish a lower temperature with a water bath than with other heating devices. Finally, the temperature of the reaction mixture will be closer to the temperature of the water, which allows for more precise control of the reaction conditions. 

Second, you must always pay attention to what is going on in your reaction flask. If the temperature of your aluminum block or sand bath equals the suggested temperature, but the solution in your flask is not boiling, you clearly will have to increase the temperature of the heating device. Remember that what really matters is what is going on in the flask, not what the textbook says The external temperature, as measured by a thermometer placed into the heating device, is not the important temperature. Far more critical is the temperature inside the flask, which may be considerably lower than the external temperature. 

Place the bulb of the thermometer as close as possible to the boiling liquid without actually touching it. The best heating device is a hot plate with either an aluminum block or a sand bath. ... 

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