Bumping, cause prevention

It may be purified by recrystallization from hot hydrochloric add, as recommended in Org. Syn. 3, 87, but on account of the difficulty of filtration this procedure is satisfactory on a small scale only. It is preferably distilled in 200-g. lots from a 500-cc. Claisen flask under 10-15 mm. pressure, b.p. 160-165V12 mm. It is important that no air inlet be used to prevent bumping, since under these conditions it partly sublimes and causes trouble by stopping up the connections. A filter or distilling flask is used as a receiver and only a short but wide bore (10 mm.) air condenser is necessary. This product is pale yellow and melts at 95-96°. The yield from 200 g. of crude product is 180-185 g-... 

To prevent any undesirable distillation and/or bumping which would cause concentration fluctuations, the procedures outlined by Juliano (19) were carefully followed. Next, each detached dilatometer was securely clamped in a constant temperature bath which was maintained at 20, 30, or 40°C as desired. Readings were taken with a cathetometer after the initial thermal expansion to the bath temperature. The data were treated as described by Pett. (20) The dilatometric treatment was also used for those reactions where a conversion versus time curve was required for later estimation of extent of conversion. 

A vigorous mechanical stirrer must be used to prevent the precipitated sodium bromide from settling to the bottom and causing bumping. 

FIGURE 2—22. If an inhibitor of the transport carrier binds to its own binding site, it prevents neurotransmitter molecules from being able to bind to their sites. This figure shows an antidepressant, fluoxetine (Prozac), binding to the serotonin transporter. When this drug binds to the serotonin transporter, it essentially bumps serotonin neurotransmitter molecules out of their seats on the transport carrier. This causes inhibition or blockade of neurotransmitter transport into the neuron. Sodium binding is also decreased, and the tires go flat, so that transport is halted. 

Heating a test tube - you must wave the test tube in the flame to prevent localized heating, which will cause the liquid to bump out of the tube. Also use an appropriate anti-bumping device and make sure that the tube is not pointing at anyone. 

C) and a receiver (R). All distilla-tions should include the addition of a few chips of a broken porous plate to prevent bumping. The vapour of the substance, which is caused to boil at a regular rate, is condensed during its passage through a... 

Neither cotton nor glass wool should be attached to part "A" ot the three-way stopcock (Figure 1), because adhesion of cerium(lll) chloride to them, caused by bumping of the powder, prevents reducing the pressure. 

Wooden applicator sticks are used in some applications. They function in the same manner as boiling stones. Occasionally, glass beads are used. Their presence also causes sufficient turbulence in the liquid to prevent bumping. 

Two remarks must be mentioned The pressure may not be coupled directly with the hydrodynamic pressure p, but must be calculated by the dry contact solution (section 2.2) and secondly the pressure p— is not a solid contact pressure, since die Reynolds equation is still valid and therefore no real solid contact spots can be identified. With this approach, the results of fig. 3 change as follows. At the fictitious solid contact spot in the center of the Hertzian contact a sharp pressure spike pnum is calculated (fig. 4) which leads to a film thickness equal to zero (fig. 5, left). Additionally, the pressure drop downstream of the bump does not reach zero as before (fig. 5, right). From the numerical point of view, these local pressure gradients cause instabilities during solution process and therefore preventing convergence. 

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