Vacuum flasks

Direct injection of liquid nitrogen is also used on the larger vehicles. This is carried in metal vacuum flasks and the vehicle will he reliant on depots where the liquid nitrogen flask can he refilled. The only mechanical equipment will he a thermostatically controlled solenoid injection valve. 

The work which led to the modern vacuum flask has been described by J. Dewar (1896). Vacuum jacketed flasks are used extensively in scientific laboratories and can be constructed relatively easily tubing is chosen to give a flask of the required size and, after the inside tube has been rounded off at one end, a Dewar seal to the outer tube is made at the other end (Figure 51,7). If a flask with a narrowed neck is required the parts must be prepared as in Figure 51, II, before the Dewar seal is made. 

In conclusion, the following experiments on filtration-washing-deliquoring should be performed to produce data (viscosity of liquids, effective solid concentration, specific cake resistance, cake compressibility, etc.) that are necessary to evaluate times of individual steps of filtration at an industrial scale, i.e. to obtain the proper basis for scale-up of filtration processes measure the filtrate volume versus time make marks on your vacuum flask and take down the time when the filtrate level reaches the mark => no more experiments are needed for preliminary evaluations of filtration properties of slurries initially fines pass the filter medium => recirculate them to the slurry,... 

Weigh 2.5 or 5 g of crop matrix into a blending vessel. Fortify samples at this point with the appropriate analytical standards. Allow the solvent to evaporate. Add 100 mL of acetone-water (4 1, v/v) and blend the mixture using an Omni mixer equipped with a macro generator for 5 min at 6000-7000 rpm. Filter the sample through a Whatman 934 AFI glass-fiber filter paper on a Buchner funnel/vacuum flask setup. Rinse the blending cup and filter cake with 100 mL of acetone. Transfer the filtrate into a 200-mL TurboVap vessel. 

Besides the reversible and irreversible processes, there are other processes. Changes implemented at constant pressure are called isobaric process, while those occurring at constant temperature are known as isothermal processes. When a process is carried out under such conditions that heat can neither leave the system nor enter it, one has what is called an adiabatic process. A vacuum flask provides an excellent example a practical adiabatic wall. When a system, after going through a number of changes, reverts to its initial state, it is said to have passed through a cyclic process. 

In fact, a truly adiabatic system cannot be attained, since even the most insulatory materials will slowly conduct heat. The best approximations are devices such as a Dewar flask (sometimes called a vacuum flask ). 

As soon as the tap is opened, molecules of hydrogen move spontaneously from the high-pressure flask to the vacuum flask. The movement of gas is usually so rapid that it makes a slurp sound, which is why we often say the vacuum sucks . 

Dissolve 20 g of the alkaloid (e.g., ergotamine) in 200 ml 1M KOH in methanol (i.e., dissolve 56 g KOH pellets in 1L 100% methanol) in a 1 L heavy walled vacuum flask and evaporate in vacuum the methanol at room temperature. To prevent the solution... 

Left, Charlie Focht of the Nebraska State Agriculture Laboratory prepares the mobile phase for an atrazine assay. Note that the vacuum flask is positioned in an ultrasonic cleaner bath. Simultaneous vacuum filtration and sonication provide a more efficient means for degassing. Right, Charlie adjusts the flow rate setting on the HPLC pump. 

Gooch, Frank Austin (1852—1929). An American chemist, noted for analytical methods, especially as the inventor of "Gooch Crucible . It is a crucible with perforated bottom packed with glass wool or asbestos and placed in a funnel inserted in the stopper of vacuum flask. Can be used for filtering corrosive liquids Ref Hackh s Diet (1944), 386-L... 

Seal off offtake 2 and spill metallic zirconium into section 5 via offtake 6. Tightly close offtake 6 with a rubber stopper. Connect the apparatus via offtake 8 to a vacuum system for 15-20 min. Next place test tube 1 into a Dewar vacuum flask with liquid nitrogen and seal off offtake 6. Perform this work wearing eye protection in the presence of your instructor ) After the pressure in the system becomes equal to 10 mmHg (in about 40-60 minutes), seal off offtake 8. Stop cooling test tube 1 and wait until the apparatus acquires room temperature. 

Extraction discs (0.5 mm thick, 25 to 90 mm diameter) constitute a variation of column-based SPE. These discs allow rapid extraction of large volumes of sample, which is not possible using a small column. The discs are made of bonded-phase silica particles, a few micrometres in diameter, trapped in a porous Teflon or glass fibre matrix. The discs are operated in a similar way to a paper filter on a vacuum flask. After extraction, the analyte is recovered by percolating a solvent through the filter. The major application of this technique is the isolation of trace amounts of compound dispersed in an aqueous medium. 

Determine the appropriate acrylamide percentage of running gel solution (see Table B3.1.1), and mix solution in a side-arm vacuum flask according to Table B3.1.2, leaving out the ammonium persulfate and TEMED. 

Using a graduated cylinder, measure 300 ml deionized water into a vacuum flask. Add 700 ml HPLC-grade acetonitrile to the flask. Mix solution with stir bar and magnetic stir plate. Degas the mobile phase daily in an ultrasonic bath under vacuum or using an in-line degasser. Prepare fresh for each analytical run. 

Gases used in a processing plant will be received either as a cylinder or as a liquid in a cryostat (large vacuum flask). 

One of the consequences of Dewar s work was his invention of the vacuum flask to minimize heat loss. It was expensive and time-consuming to liquefy gases hence, Dewar designed a container where, once liquefied, gases could be kept for as long as possible. Still known as the Dewar flask among chemists, it is more widely known as the Thermos, named after the company that obtained the patent for the flask and to whom Dewar lost an ensuing court case. 

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