Stopcock, glass Teflon

Chromatography columns 100 x 15-mm i.d. with Teflon stopcock Glass-fiber filter (Whatman GF/D, 11-cm)... 

Gas chromatograph, equipped with a nitrogen-phosphorus detector Glass chromatography column, 19 x 300 mm with Teflon stopcock Glass wool (Pyrex)... 

Fig. 4. Schematic vacuum system for metal atom reactions. X represents the stopcock or Teflon-in-glass valve. Satisfactory components (for a general discussion of vacuum line design see References 1 and 4) forepump, 25 L/min free air capacity diffusion pump, 2 L/sec main trap is removable and measures about 300 mm deep main manifold has a diameter of about 25 mm, stopcock or valve in manifold should be at least 10 mm substrate container is removable container with 1-2 mm Teflon-in-glass needle valve connected to bottom of container. Connection between this needle valve and the reactor may be 1/8 in. od. Teflon tubing is used. Alternatively, the substrate may be added as shown in Fig. 3.

Modified Parfait Protocol. Teflon adsorbents were cleaned by 24-h extraction with acetone in a Soxhlet apparatus and stored in acetone. Cleaned Chromosorb T was used to fill a 150-mL silanized addition funnel equipped with a 24-40 male joint on the bottom. A plug of silanized glass wool supported the bed just above the stopcock. The Teflon bed was compressed slightly with a large stirring rod to keep the top of the bed in place while the bed was washed with at least 6 bed volumes (900 mL) of high-purity water. The washed Teflon was kept covered with water and used immediately. 

Figure 1. Apparatus for sealing NMR tubes (A) cajon fitting (B) vacuum stopcock with teflon plug (C) ground glass joint.

Like other germanes, methyldigermane dissolves in stopcock grease and reacts slowly with mercury. Ideally, it is handled in an all-glass or glass-Teflon system, but little difficulty will be experienced in using a conventional vacuum line for any of the alkyldigermanes. 

Because of difficulties in adjusting an ordinary glass stopcock to avoid leakage and to maintain a drop rate that would add the un-saturated cyanoester solution over a 40-hour period, the checkers recommend the use of a funnel equipped with a Teflon stopcock. 

Today, the glassware required consists of either a round-bottom flask or a Schlenk tube serving as the reaction chamber. This chamber is equipped with a magnetic stirbar and a Teflon high-vacuum valve (or glass stopcock) which provides for easy vacuum control after attachment to a vacuum line (Fig. 8.7). 

After the Teflon stopcock is closed, the reaction vessel is transferred to a water bath maintained at 60°. The lower end of the vessel should be immersed to within about 1 in. below the fritted-glass retainer. As refluxing of the bromine proceeds, a liquid layer should accumulate above the fritted-glass retainer. If this does not happen, some bromine should be poured through the bypass arm so that a liquid layer ca. 1 in. thick is maintained on the frit. It is essential that liquid bromine contact the tribromide in order to attain efficient conversion to tetrabromide. As the reaction proceeds, the product, dissolved in liquid bromine, extracts into the lower vessel and deposits there as fine black crystals. 

FIGURE 4.14 The three styles of buret stopcocks. Left, all Teflon center, Teflon stopcock and glass barrel right, all glass. 

Leakage A burette must be tested for any sort of leakage before putting it into operation. Teflon stopcocks are usually adjusted by a knurled nut for perfect use. Glass stopcocks may require a small quantity of a special type of grease or lubricant to allow both ease of operation and to check leakage. 

Outlet Tip From a practical point of view the outlet tip of either types of burette, i. e., having Teflon or glass stopcocks, must be of such diameter and taper as to allow the delivery of a single drop whose volume is significantly less than that which can be held between any two finest graduations of the scale with which the burette is calibrated. 

Fig. 1. All dimensions in centimeters, (a) 2-cm-thick glass wool plugs (b) IrCl3 on silica gel (c) Pyrex jacket for thermocouple (d) 24/40 J joint (e) Kontes 24/25 Teflon adapter with O-ring seals (f) thermocouple leads to indicating controller (g) outlet to H2S04 bubbler by way of trap (h) 2-mrri double oblique Teflon stopcock (i) N2 inlet (/ ) CO or Cl2 inlet.

Ground glass joints were connected using Teflon sleeves or a chlorofluorocarbon stopcock grease. 

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