Stopcocks retainer

C. Stopcocks for Pressure and Vacuum. In a typical Schlenk system, the apparatus is repeatedly exposed to a small positive pressure and to vacuum. This causes stopcocks to become dislodged therefore, satisfactory performance requires good stopcock retainers. An excellent retainer design is illustrated in Fig. 8.8. This particular retainer requires the use of the stopcock produced by the same manufacturer.6... 

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. 

K diebromate soln in it), serving to count the number of bubbles of air entering thru stopcock Rg and to retain any gas or vapor which might adversely affect the analysis B — Round bottom flask, called "un ballon de saponification ... 

Heated air is admitted by a pipe furnished with a stopcock, also steam to retain the compound moist, and carbonic acid from any convenient generator. Provided the temperature be retained at 96°, or thereabouts, the conversion of the lead will be effected in ten days or a fortnight. The salified mass is then removed and ground, then agitated with water, and any metal which separates returned to tha chamber with flesh acid. 

Excellent retainers (K-809000). which must be used with stopcock plugs from the same manufacturer, are available from Kontes Glass Co. Vineland NJ. 

Fig. 8.8. Retainer stopcocks for vacuum and pressure. This style of stopcock (Koutes Inc.) is especially useful on a Schlenk manifold where both vacuum and small positive pressures of inert gas are used, (n) The retainer is being snapped onto the base of the stopcock plug, (b) The knurled nut has been tightened to hold the plug in place.

An excellent stopcock and retainer design tor use with Schlenk systems is available from Kontes Glass Co. (address in footnote 1). 

Precision made stopcocks, with interchangeable ground glass keys, are usually fitted with key retainers to prevent accidental loss or breakage during storage and use. 

When the fluorination has been completed, stopcocks BS and RS are closed, and the entire manifold is evacuated and rinsed with dry air ten times and then retained under diminished pressure.7 The condenser of the fractionating column B is precooled to the boiling temperature of the most volatile reaction product. This is achieved by manually closing relay RP of an electronic control circuit. The control leads of this circuit are connected to manometer MS in such a way as to be actuated at the pressure desired for distillation. 

Approximately 125 ml. of anhydrous ether is placed in a dry,f 250-ml. Erlenmeyer flask which is equipped with a 24/40 S.T. joint and a sidearm gas inlet (see Fig. 7). The stopcock on the sidearm is fitted with a retainer clip, the flask is stoppered, and the stopper is held in place with a spring clamp. The flask is weighed and is then attached to a lecture bottle of boron(III) chloride, % as shown in Fig. 7, by means of a 1-foot length of Tygon tubing which is punctured with a needle at least four times to allow release of excess pressure of boron(III) chloride. This apparatus is set up in the hood. The boron(III) chloride cylinder is opened cautiously, and BC18 is delivered into the flask for approximately 3 minutes while the flask is shaken vigorously to facilitate solution of the gas in the... 

All operations involving chromium(II) compounds must be carried out in the complete absence of atmospheric oxygen. The apparatus is assembled as shown in Fig. 21.f All the stopcocks and ball joints are fitted with retaining clips to prevent accidental opening when the apparatus contains nitrogen pressure in excess of 1 atmosphere. ... 

Teflon stopcock F is now closed and the solvent vapor forced to pass through the frit into the upper chamber where it condenses. After about one-half of the solvent has thus been distilled into the upper chamber, the vessel is inverted, and the highly soluble KfNb(NCS)e] passes into chamber C, while the relatively insoluble potassium chloride is retained by the frit. Even though potassium chloride is quite insoluble in acetonitrile, it shows appreciable solubility in the solution of K[Nb(NCS)6] due to the increased ionic strength of the solvent. Thus, the distillation of some of the solvent into the upper chamber before filtration reduces the amount of potassium chloride contamination in the final product. 

The apparatus consists of a glass column mounted vertically on a ring stand. The column has a glass frit to retain the gel and a stopcock to adjust the flow rate. The agglutinating activity is determined by reacting rabbit red blood cells with the agglutinin and noting the amount of precipitate formed on a spot plate. Protein content is obtained by spectrophotometric measurement. 

Petroleum (16). Where applicable, samples are distilled and the 200°C+ fraction retained, spiked with 14C BaA and BaP, and analyzed for PNA content. Samples are first separated on Attapulgus clay to remove the very polar heteroatom portion of the sample. The Attapulgus clay was purchased from the National Bureau of Standards to have adsorptive characteristics as specified in ASTM D 2007. The column, 760 mm X 22 mm, is fitted with a 500-mL reservoir and a Teflon stopcock 170 g of clay is placed in the column and prewet with 50 mL of n-pentane. A 15- to 20-g sample, dissolved in 100 mL of pentane, is placed on the column. The sample is then successively eluted with 600 mL of n-pentane and 500 mL of acetone. The entire separation is carried out in a blanket of nitrogen. Each fraction is carefully evaporated on a steam bath under nitrogen until a constant weight is obtained. 

We can discuss here only a few of the numerous recommendations on how to introduce small quantities of gas into a vacuum, while retaining precise control over the flow. In many cases it is sufficient to file fine grooves in the plug of a glass stopcock, starting at the bore. In these cases, stopcocks with inclined bores (offset arms) should be used as much as possible. The Bodenstein valve is also usable for fine control, although the adjustment is not exactly reproducible. A metal needle valve is the best means of control. 

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