Organic 2 Review Problem 19

Organic 2 Review Problem 19 - wider capillary (say 2 mm. in...

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METHODS AND MANIPULATION 3 3 cm. square. (A supply of the fragments in a dust-tight box should always be freely available in the laboratory.) To fill the capillary with the compound the melting-point of which is to be determined, about 0-05 g. of the compound is placed on one of the fragments of plate, and crushed to a fine powder by gently rubbing it with the flat end of a porcelain spatula or (better) with the slightly bent end of a small flat narrow metal (e.g., nickel) spatula. When a very fine powder has been obtained, sufficient is trans- ferred to the capillary tube (by pushing the open end of the tube through the powder and backing the latter if necessary with the spatula) so that, when the closed end of the tube is tapped on the bench, a length of about 5 mm. of fairly tightly packed material has accumulated at the bottom. This is a rapid operation when the compound gives a fine dense powder: some compounds how- ever, even when pure, have a waxy consistency, and are not easily inserted into a tube of the usual width, in which case a slightly
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Unformatted text preview: wider capillary (say 2 mm. in diameter) may have to be used. The student should soon be able by experience to select a suitable tube having once obtained the "feel" of the material when crushed on the porcelain. Should the material be inclined to stick in the tube, it can often be rapidly conducted to the bottom by vibrating the tube gently by the cross-wise action of a blunt file or the milled edge of a coin. The usual apparatus for heating the substance is shown in Fig. I(B), and consists of a long-necked hard-glass flask D to which a thermometer E is fitted by means of a cork having a shallow vertical groove F cut or filed as shown to allow expansion of the contents of D. The best liquid for placing in D is medicinal paraffin, which possesses the following very suitable properties: (a) it has a low specific heat and therefore the tem-perature can be easily increased using only a small flame, (b) even when hot it FIG. i. RB |J RB (B)...
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This note was uploaded on 09/19/2011 for the course CHM 2211 taught by Professor Castalleano during the Fall '06 term at University of Florida.

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