Stopcocks high-vacuum

The distinguishiag features are (i) the special stopcock is constructed to turn easily under a high vacuum (ii) a moulded arrow on the stopcock indicates the open position, euid a quarter turn from this position closes the desiccator and (iii) a special liquid container of the non-spill type. 

Fig. A.5. An apparatus for the lsO-labclling of the CO2 produced in biolumines-cence reactions. The stopcocks A-E and the ground joint of reaction vessel are lubricated with high-vacuum grease, and the connections between the glass tubes are made with short pieces of thick-walled silicon rubber tubing. The stopcocks C and D are high-vacuum type, such as Ace Glass, Cat. No. 8197-04 and 8195-236, or Corning, Cat. No. 7473-3.

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). 

Fig. 10. Apparatus for the sublimation of decaborane. (A) cold finger (B) ground-glass joint for connection to high-vacuum system (C) high-vacuum stopcock ...

Shriver, D. F. "The Manipulation of Air-sensitive Compounds McGraw-Hill New York, 1969. The high vacuum stopcock is available from J. Young Scientific Glassware Ltd. (11 Colville Road, Acton, London W3 8 BS, UK). 

A J. Young high vacuum stopcock was purchased from Aldrich Chemical Compay, Inc. 

If visual inspection of the most suspect joints or stopcocks fails to reveal the leak, a systematic isolation of parts of the vacuum system is in order. For a vacuum line of conventional design (e.g., a line approximating that in Fig. 5.2), it is generally best to turn off all stopcocks which interconnect the various parts of the vacuum system. As a result, the high-vacuum manifold is isolated from the pumps and the rest of the line, and it is checked by determining if there is a steady pressure rise in that section. If this section appears to be intact, but it... 

It is best to evacuate a freshly greased system at least several hours before it is to be used and to work in the stopcocks by occasionally turning them. When high vacuum is required, it is usually advantageous to evacuate the system overnight and to flame the glass, exclusive of stopcocks and joints, to desorb moisture. 

In the following procedures a standard glass vacuum line with high-vacuum stopcocks (lubricated with Kel-F-90 grease ) is used. Because of the reactivity of many of the compounds with mercury, it is convenient to use a null-point pressure device, such as a Booth-Cromer16 pressure gage or spiral gage. A mercury manometer covered with Kel-F-3 oil can be used. 

Then 10 to 15 g. of the anhydrous disodium monoamido-phosphate is weighed in a 50-ml. flask with a glass joint. The flask is attached to a high-vacuum system, via a stopcock and a trap filled with solid sodium hydroxide, and evacuated. The flask is then heated in an oil bath to 80° and this temperature maintained for 6 hours. The temperature is then raised, and pressure builds up from the ammonia liberated. This gas is pumped off at intervals and the temperature increased to 210°. The formation of ammonia slows down after some time, and the reaction comes to an end after about 7 days. 

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