Vacuum desiccators exhaustion

Drying is more rapid in a vacuum desiccator of the design shown in Section 2.11. When exhausting a desiccator a filter flask trap should always be inserted between the desiccator and the pump. The vacuum should be applied gradually and the precaution taken of surrounding the desiccator by a cage of fine-mesh steel wire (DesiguardU) the collapse of the desiccator will then do no harm. 

All carbons used in this research were pretreated to remove fines by sonication (Bransonic 220, Branson Cleaning Equipment) for 30 seconds followed by a rinse with Type I reagent-grade water (Millipore Corp). Coal-based carbons were then extracted with 2-N HCl in a soxhlet extractor for 42 hours to remove ash components and alkaline impurities. After extraction, the sample was boiled for four hours, then exhaustively rinsed until the pH of the suspension was in the range 5 to 6. All carbon samples were dried at 100 °C under vacuum, and stored in a vacuum desiccator. 

Place all beakers containing soil and chloroform in a vacuum desiccator, the inner surface of which is lined with moistened filter paper. Do not use plastic desiccator. Properly seal the lid-joint using high density vacuum grease. Use a rubber tube to direct the exhaust through water. 

The dry methosulfate, dissolved in about 30 ml. of water, is made alkaline with 2-3 ml. of 10% sodium hydroxide, and the solution is then extracted exhaustively with successive 15-ml. portions of chloroform until no more blue substance is removed from the aqueous solution (Note 12). The combined chloroform solutions are extracted three times with 20-ml. portions of 5% hydrochloric acid. The combined acid extracts are made alkaline to phenolphthalein with 10% sodium hydroxide and reextracted exhaustvaely with 25-ml. portions of chloroform until no more blue substance is removed from the aqueous solution (Note 12). The combined chloroform solutions are dried over anhydrous sodium sulfate and decanted, and the chloroform is removed by distillation under reduced pressure. The blue crystalline residue is recrystallized by dissohnng it in the least possible amount of water at 60° and then cooling the solution in an ice bath. The product is filtered on a 5-cm. Buchner funnel and dried in the dark in a vacuum desiccator over calcium chloride. The yield is 1.35 g. (58%) of dark blue needles that melt at 133° (Note 13). 

Mechanical Pumps. Perhaps the most common form of vacuum pump is a mechanical pump that operates with some sort of rotary action, with moving parts immersed in oil to seal them against back-streaming of exhaust as well as to provide lubrication. These pumps are used as forepumps for diffusion pumps. Other common laboratory applications are the evacuation of desiccators and transfer lines and distillation under reduced pressure. These pumps have ultimate pressures ranging from 10 to 0.05 Torr, and pumping speeds from 0.16 to 150 L s or more, depending on type and intended application. 

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