Organic 2 Review Problem 47

Organic 2 Review Problem 47 - in the apparatus, the...

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METHODS AND MANIPULATION To pump FIG. 13. fractions without interruption of the distillation. The "pig" consists of a stout glass receiver A, which fits either over the side-arm of the Claisen flask or, in the case of low-boiling liquids, over the end of the condenser which is fitted to this side-arm. It has at the top an outlet tube B for connection to the manometer and pump, and at the lower end usually three outlet tubes to which are fitted consecutive receivers C, D, E. When distillation starts, the "pig" is so placed that the first fraction collects in C. When the second fraction starts to distil, A is rotated slightly to bring the outlet tube leading to D in the lowest position, so that the second fraction collects in D: further rotation then causes the third fraction to collect in E. The apparatus however often gives unsatisfactory results, particularly in the hands of students, who frequently find that if a good vacuum is obtained
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Unformatted text preview: in the apparatus, the "pig" sticks firmly around the cork F and refuses to rotate: conversely, easy rotation around this cork usually means a leaky joint at this point, and an unsatisfactory and varying pressure is recorded by the manometer. (The ground-glass fitting B shown in Fig. 23(p), p. 46, avoids this trouble.) For general work, a very satisfactory apparatus for collecting fractions under reduced pressure is the Perkin triangle C,* which is shown in Fig. 14, together with the requisite fittings for the complete To pump FIG. 14. * G. A. R. Kon (your. Chem. Soc., 1930, 182) described a modification of the Perkin triangle having only two taps instead of the three described above. It may be purchased from Quickfit & Quartz, Ltd., Quickfit Works, Stone, Staffs....
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