Glass filters

Filter the product at the pump, using an alkali-resisting filter-paper, or a sintered glass filter-funnel. Wash the crystals on the filter with a small quantity of ethanol to remove the purple colour, and then drain thoroughly. 

Collecting the silver halide. Meanwhile assemble the apparatus shown in Fig. 91. G is a filter-funnel having a sintered glass filter-plate... 

A simple apparatus for sublimation in a stream of air or of inert gas is shown in Fig. II, 45, 3.. d is a two-necked flask equipped with a narrow inlet tube B with stopcock and a wide tube C 12-15 inm. in diameter. The latter is fitted to a sintered glass crucible and the usual adapter and suction flask E. A well-fitting filter paper is placed on the sintered glass filter plate to collect any sublimate carried by the gas stream. 

Crystd from hot water (4mL/g at 65°), then dried in a vacuum desiccator over CaS04. Phillips and Taylor [J Chem Soc 4242 7962] cooled an aqueous solution of KMn04, saturated at 60°, to room temperature in the dark, and filtered through a No.4 porosity sintered-glass filter funnel. The solution was allowed to evaporate in air in the dark for 12h, and the supernatant liquid was decanted from the crystals, which were dried as quickly as possible with filter paper. 

Figure 1. A, Dewar flask B, sintered glass filter C, metal cooling coil D, water inlet E, water outlet F, reaction vessel < , quartz immersion well /f, pyrex filter /, lamp ...

The cold solution was then allowed to stand overnight and all crystalline material filtered through a sintered glass filter. The filtrate was treated with an additional 300 ml of concentrated hydrochloric acid to yield a heavy white precipitate. The precipitate was filtered, dried and combined with the Initial precipitate obtained as described above. The combined precipitated product, 3A-dihydroxy-N-[3-(4-hydroxyphenyl)-1-methyl-n-propyl-/ henethylamine hydrochloride, had a melting point of about 184°Cto 186°C after recrystallization from boiling 4N hydrochloric acid. 

One hour after addition of the tetracycline, the clear reaction solution was poured into 1,500 ml of chloroform. A yellow product separated and was collected on a coarse sintered glass filter and air dried. The tetracycline-metaphosphoric acid complex weighed about 10 grams, contained 7.34% of phosphorus and had a bioassay of 634 gammas per milligram. Solubility in water is 750 mg/ml. 

After 30 minutes the solid sulfinic acid is separated on a fritted-glass filter. The sulfinic acid is dissolved from the filter by a mixture of 750 ml. of ether and 750 ml, of methylene chloride. The solution is dried over calcium chloride and evaporated to dryness under reduced pressure (bath temperature 25°) (Note 5). The residue is suspended in 50 ml. of water, and small portions of dilute ammonia are added to the well-stirred suspension until it has a pH of 9 (Note 6). Insoluble impurities are separated by filtration, and 2-nitrobenzenesulfinic acid is precipitated from the filtrate by adding 5-ml. portions of 6N hydrochloric acid with cooling the sulfinic acid precipitated by each portion of acid is separately collected on a Buchner funnel (Note 7). The acid, a pale yellow solid, is dried on a clay plate in a vacuum desiccator over potassium hydroxide pellets, m.p. 120-125° (dec.), weight 9.4-14.9 g. (50-80%). If the 2-nitrobenzenesulfinic acid is to be used for the hydrogenation of the next step high purity is required, and it is generally advisable to reprecipitate the acid once more in the same way (Note 8). 

This operation is the separation of the precipitate from the mother liquor, the object being to get the precipitate and the filtering medium quantitatively free from the solution. The media employed for filtration are (1) filter paper (2) porous fritted plates of resistance glass, e.g. Pyrex (sintered-glass filtering crucibles), of silica (Vitreosil filtering crucibles), or of porcelain (porcelain filtering crucibles) see Section 3.24. 

Pipette 25.0 mL of the bromide ion solution (0.01-0.02M) into a 400 mL beaker, add excess of dilute silver nitrate solution, filter off the precipitated silver bromide on a sintered glass filtering crucible, and wash it with cold water. Dissolve the precipitate in a warm solution prepared from 15 mL of concentrated ammonia solution, 15 mL of 1M ammonium chloride, and 0.3 g of potassium tetracyanonickelate. Dilute to 100-200 mL, add three drops of murexide indicator, and titrate with standard EDTA (0.01 M) (slowly near the end point) until the colour changes from yellow to violet. 

Precipitate about 0.1 g potassium (present as potassium chloride in 50 mL water) with 40 mL of the sodium TPB solution added slowly and with constant stirring. Allow to stand for 30 minutes, filter through a sintered-glass filtering crucible, wash with distilled water, and dry for 1 hour at 120 °C. Shake 20-25 mg of the dry precipitate with 200 mL distilled water in a stoppered bottle at 5-minute intervals during 1 hour. Filter through a Whatman No. 40 filter paper, and use the filtrate as the wash liquid. 

Saturated calcium hydroxide solution. Shake a large excess of finely divided calcium hydroxide vigorously with water at 25 °C, filter through a sintered glass filter (porosity 3) and store in a polythene bottle. Entrance of carbon dioxide into the solution should be avoided. The solution should be replaced if a turbidity develops. The solution is 0.0203M at 25 °C, 0.0211 M at 20°C, and 0.0195M at 30 °C. 

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