Melting point capillaries , preparation

No glass melting point capillaries need be prepared. 

The student should read Sections 1,10 to 1,16 carefully before commencing any experimental work. A supply of melting point capillaries is prepared as described in Section 11,10 (compare Fig. 77, R , I). The apparatus illustrated in Fig. 77. 10, 2, a is assembled with concentrated sulphuric acid as the bath liquid the thermometer selected should have a small bulb. The melting points of pure samples of the following compounds are determined in the manner detailed in Section 11,10 —... 

Purification of the radioactive tracer was modified to include a fractional sublimation before a single extraction—recrystallization cycle to conserve the tracer material. Microgram samples were prepared in melting point capillaries for assay by mass spectroscopic analysis (Table III), made by direct probe injection of the sample into the ion source (18). The probe was heated rapidly to 200°C, and mass spectra were obtained during vaporization of the sample. Tri-, tetra-, and pentachlorodibenzo-p-dioxins vaporized simultaneously with no observed fractionation. 

Hence pure anhydrous tris(benzoylacetonato)europium(III) is difficult to prepare. The best conditions found for dehydration were to heat the dihydrate for about an hour at not over 70° in a vacuum oven (at 30 mm.). Calculated for Eu(CioH902)3 C, 56.7 H, 4.28 Eu, 23.9. Found C, 55.5 H, 4.26 Eu, 23.9. The low carbon analysis indicates that some hydrolysis occurs even under these mild conditions. The anhydrous compound is fight yellow, and in a melting-point capillary it softens at about 70° and melts at about 90° to a viscous liquid. 

Under similar conditions, 1 reacts with Na2Se to give PPSe in only 5% yield. When prepared as noted above and with Se in DMF, PPSe is a yellow powder with a melting point (capillary tube) of ca. 220° and a compositional range, from elemental analysis,... 

Microscale Inverted Capillary Method. In microscale experiments, there often is too little product available to use the semimicroscale method just described. However, the method can be scaled down in the following manner. The liquid is placed in a 1-mm melting-point capillary tube to a depth of about 4-6 mm (see Figure 13.4B). Use a syringe or a Pasteur pipette that has had its tip drawn thinner to transfer the liquid into the capillary tube. It may be necessary to use a centrifuge to transfer the liquid to the bottom of fhe tube. Next, prepare an appropriately sized inverted capillary, or bell. 

An alternative technique for preparing the glass bells follows heat the midsection of an open-ended melting point capillary tube and then draw the glass to form a smaller capillary section. This section is then broken approximately in the middle and each open end is sealed. The appropriate length for the bell is then broken off. Thus, two bells are obtained, one from each section. The sealing... 

Pyrex glass is preferable, but this requires an oxy-coal gas blowpipe for manipulation. Suitable melting point tubes may be purchased from dealers in scientific apparatus or chemicals. It is, however, excellent practice, and an essential part of his training, for the student to learn to prepare bis own capillary tubes. 

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