Test tube wall

Dichromate oxidation of secondary alcohols produces ketones in good yield, with little additional oxidation. For example, CH,CH2CH(OH)CH3 can be oxidized to CH CH2COCH3. The difference between the ease of oxidation of aldehydes and that of ketones is used to distinguish them. Aldehydes can reduce silver ions to form a silver mirror—a coating of silver on test-tube walls—with Tollens reagent, a solution of Ag1" ions in aqueous ammonia (Fig. 19.3) ... 

Coating the Test Tube Walls with Silver. Mix the ammonia solution of silver with the glucose solution in the proportion 10 1. Pour 4-5 ml of the reaction mixture into the prepared test tube and lower the latter into a beaker with warm water (50-60 C). What do you observe Write the equations of the reactions. How can the walls of the tube be cleaned of the deposited silver ... 

Figure 3.6 shows the same effect if the same liquid levels for different viscosities at the corresponding times are compared (dotted blue line). Absolute values of the liquid level in the test tube cannot be determined with a dimensional analysis, because other parameters (the test tube wall) would have to be taken into account... 

In Vitro Clotting Tests. The plasma recalcification time of citrated human plasma was determined in the presence of heparin-PVA beads and control PVA beads without heparin. Various amounts (10-200 mg) of gel were incubated with 0.5 mL of plasma at room temperature for 5 min. After the addition of 0.5 mL of0.025M CaCl2, the time to clot was noted by tilting the test tube gently each minute, until the beads clumped together or were found to stick to the test tube wall. 

SaPlSaPlSb (clumps adhere to protein-coated test tube wall, PlSb). 

Figure 5.7 Spatiotemporal distribution of the degree of conversion. The front is initiated at the test tube wall (r = 8) and moves toward the tube axis (r = 0). The profiles are shown over equal time intervals. Densely drawn profiles propagating to the left from the test tube wall toward the axis correspond to the isothermal mechanism of propagation,...

We describe cases when FP is expected to be observed. The first case is the polymerization of crosslinking monomers (thermosets). The second group of monomers form polymers that are insoluble in the monomer. Good examples are acrylic and methanylic adds. Insoluble polymer particles adhere to each other during thdr formation and stick to the reactor or test tube walls, forming a mechanically stable phase and discernible polymer-monomer interface. Nonetheless, Rayleigh-Taylor and double-diffusive instabilities, which we will discuss... 

Place 0-5 g. of the amino acid and 1 0 g. of phthalic anhdride in a Pyrex test-tube and immerse the lower part of the tube in an oil bath, which has previously been heated to 180-185°. Stir the mixture occasionally during the first 10 minutes and push down the phthalic anhydride which sublimes on the walls into the reaction mixture with a glass rod. Leave the mixture undisturbed for 5 minutes. After 15 minutes, remove the test-tube from the bath when the liquid mass solidifies, invert the test-tube and scrape out the excess of phthalic anhydride on the walls. RecrystaUise the residue from 10 per cent ethanol or from water. 

If preferred, suitable ignition tubes may be prepared by the student from soft glass tubing it is important that the thickness of the glass at the closed end be tmiform, otherwise the tube is likely to crack when heated. The simplest procedure is to blow a small bulb of uniform wall thickness at the end of the tube. The small test-tubes are available from all laboratory supply dealers... 

Arsenic. The presence of arsenie in an organie eompound is generally revealed by the formation of a dull grey mirror of arsenic on the walls of the test-tube when the eompound is fused with sodium in the Lassaigne teat. Usually sufficient arsenic is found in the fusion solution to give a yellow precipitate of arsenic trisulphide when the solution is acidified with hydrochloric acid and treated with hydrogen sulphide. 

Identification. If accessible, defects from burnthrough may be visually identified as fused holes in the tube wall. Various nondestructive testing techniques, such as radiography and ultrasonics, may also detect this defect. The defect generally causes leakage soon after affected equipment is placed in service. 

The furnace was fitted with interlocks that should have isolated the fuel supply if the tube wall temperature or the pressure of the heat transfer oil got too high. Neither interlock worked, and neither had been tested or maintained. The set-point of the high tube wall interlock had been raised far above its original set-point, from 433°C to 870°C, a simple way of putting it out of action [15]. Changing the set-point of an interlock is a modification and should be allowed only when the equipment is capable of withstanding the new conditions (see Chapter 2). 

Reactions under pressure are usually carried out in an autoclave. However, several simple vessels can be used for reactions at moderate pressure. A heavy walled Pyrex test tube or Kjeldahl flask drawn out and sealed with an oxygen torch makes a suitable container for many Diels-Alder reactions. The tube can be heated in an oil or water bath, but care must be exercised to protect against explosions. At the conclusion of the reaction, the tube is cooled to room temperature, the neck is scratched with a file or carborundum chip, and a hot Pyrex rod is touched to the scratch. A large crack in the neck should result, and the sealed top can be easily knocked off. 

The catalyst in an isothermal tube-wall reactor (experiment TWR-6 in Ref. 2) deactivated much more slowly than did the catalyst in the best test (experiment HGR-14) in an adiabatic HGR reactor (0.009 vs. 0.0291 %/mscf/lb), and it also produced much more methane (177 vs. 32 mscf/lb catalyst). This indicates that adiabatic operation of a metha-nation catalyst between 300° and 400°C is not as efficient as isothermal operation at higher temperature ( 400°C). 

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