Drying of glassware

Another piece of glassware used in synthetic procedures is the cold finger condenser (Fig. A3.7). Used in the case where the reaction is carried out in a low-boiling solvent (for example, liquid ammonia), the condenser is filled with a suitable cooling mixture and fitted with a drying tube. 

There are all sorts of variations, but they boil down to this Y ou ve taken all this time to dry your glassware only to put water in it. Writers of lab manuals are very tricky about this. Perhaps they say you ll be using steam. Or maybe 5% aqueous sodium bicarbonate solution. Or even that a byproduct of your reaction is H20. Condense steam and you get what An aqueous solution has what for a solvent H20 is what ... 

Samples containing heavy oil, along with the volatile components can severely contaminate pnrge-and-trap instrumentation, and caution is advised when interpreting the data. For such samples it may be advisable to use a separatory funnel for the water extraction method for semivolatiles (EPA 3520). In this method, the sample is ponred into a funnel-shaped piece of glassware, solvent is added, and the mixtnre is shaken vigorously. After layer separation, the extract (i.e., the solvent layer) is removed. Altered, dried with a desiccant, and concentrated. Multiple extractions on the same sample may increase overall recovery. 

To prevent partial hydrolysis of the lithium aluminum hydride, the checkers found it desirable to dry the glassware by flaming while dry nitrogen was being swept through the apparatus. 

D. R. Burfield and G. Hefter, Oven Drying of Volumetric Glassware, ... 

As we have pointed out previously, oxygen and water concentrations can be kept at extremely low levels with a properly maintained purification train. In fact, contamination by water is much more easily controlled in a dry box than on a vacuum line. This may result in part from the number of operations and manipulations necessary to use a vacuum line. The oxidation of the cation radical of thianthrene to the dication illustrates this point. The dication is very electrophilic and is rapidly attacked by any nucleophiles (e.g., water). The electrochemistry of the dication in solutions prepared in the dry box (with acetonitrile as the solvent purified as described earlier) is reversible if a little care is taken in preparing the solvent and in drying the glassware. It is more difficult to obtain such reversible behavior when solutions are prepared on a vacuum line. 

Heat is the most widely used means of sterilization, which can be employed for both liquid medium and heatable solid objects. It can be applied as dry or moist heat (steam). The moist heat is more effective than the dry heat, because the intrinsic heat resistance of vegetative bacterial cells is greatly increased in a completely dry state. As a result the death rate is much lower for the dry cells than for moist ones. The heat conduction in dry air is also less rapid than in steam. Therefore, dry heat is used only for the sterilization of glassware or heatable solid materials. By pressurizing a vessel, the steam temperature can be increased significantly above the boiling point of water. Laboratory autoclaves are commonly operated at a steam pressure of about 30 psia, which corresponds to 121°C. Even bacterial spores are rapidly killed at 121 °C. 

Drying Ovens. These units are used to facilitate the drying and storage of glassware that needs to be dry and ready at a moment s notice. Drying ovens are also used to dry samples for weighing. 

Dry all glassware and the stirrer bar in an 105°C electric oven for 2 h and allow the glassware to cool down under an atmosphere of dry nitrogen. 

Dry all glassware for at least 2 h in an oven at 150°C, assemble the round-bottomed flask and condenser while still warm, immediately attach a calcium chloride guard tube to the top of the condenser and stopper the second neck. 

Dry all glassware for 2 h in an oven at 105°C, assemble the round-bottomed flask, pressure-equalising addition funnel, condenser, magnetic stirrer bar and nitrogen bubbler while still warm, and immediately connect the nitrogen supply so that a flow of the gas passes through the equipment. 

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