Teflon stopcock

Teflon Stopcocks. Teflon stopcocks should never be stored with the locking nut tightened. Teflon flows under pressure, and such pressure could squeeze the plug up and into the holes of the barrel (see Fig. 3.29). Teflon plugs are tapered at a 1 5 ratio rather than the 1 10 ratio of glass stopcocks to help relieve some of these pressures. 

Class A conforms to specifications in ASTM E694 for standard taper stopcocks and to ASTM E287 for Teflon or poly-tetrafluoroethylene stopcock plugs. The 10-mL size meets the requirements for ASTM D664. ... 

Reference is again made to the Teflon stopcocks and to the diaphragm type of burette tap which do not require lubrication. 

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). 

Column, chromatographic, 300 mm x 19-mm i.d. with Teflon stopcock Filter flask, 500-mL... 

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)... 

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. 

Fig. 55 Extreme closeup of teflon stopcock popping ritual.

An attempt to place the wrong size or taper Teflon stopcock into the funnel. This is extremely rare. Get a new funnel. 

C. [18]Annulene. In a 300-ml. conical flask fitted with a side arm (with a closed stopcock) and a 3.5-cm. Teflon -coated magnetic stirring bar is placed 1 g. of a 10% palladium-calcium carbonate catalyst (Note 20) and 30 ml. of benzene (Note 10). The flask is attached to an atmospheric pressure hydrogenation apparatus, and the air in the system is replaced by hydrogen by evacuating the flask and refilling with hydrogen three times. The catalyst suspension is stirred until no more gas is absorbed. One-third (390 mg., determined spectroscopically)... 

A custom-made Pyrex cell [169] was used to generate selenium hydride. The internal purge gas supply line to the furnace was routed through a stopcock made of Teflon that permitted the operator to select gas flow into either the bottom of the hydride cell or into the furnace, as illustrated in Fig. 12.11. 

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. 

A dropping funnel with a needle valve, NORMAG type 8056, manufactured by NORMAG GmbH, D-6238 Hofheim, FRG, has been used by the submitters. The checkers used a standard pressure-equalizing dropping funnel with a Teflon stopcock. 

Typically, a Pyrex or quartz reaction vessel (normally fitted with a greaseless Teflon stopcock) is inserted into an aluminum heating block. Shts are cut into the side of the block in order to allow the incident X-ray beam in and... 

A. Checkers Handling Procedure. Figures 1 and 2 suggest the equipment to be used, and how to assemble it. The hose end fitting is connected to the stopcock with a piece of Teflon lined tubing and fastened with copper wire. The stopcock should be well greased and held secure by means of a taut rubber band... 

---