Witt filter plate

The apparatus depicted in Fig. 11,34, 1, intended for advanced students, may be used for the filtration of a small quantity of crystals suspended in a solvent either a Hirsch funnel or a glass funnel with Witt filter plate is employed. The mixture of crystals and mother liquor is filtered as usual through the funnel with suction. Rotation of the three-way tap wifi allow air to enter the filter cylinder, thus permitting the mother liquor to be drawn oflF by opening the lower tap. The mother liquor can then be applied for rinsing out the residual crystals in the vessel, and the mixture is again filtered into the cylinder. When all the crystals have been transferred to the funnel and thoroughly drained, the mother liquor may be transferred to another vessel the crystals may then be washed as already described (Section 11,32). 

The solid in the tower may be supported on a Witt filter plate, but a plug of glass wool is satisfactory the plug of glass wool above the solid acts as a filter for fine particles of the desiccant. 

Filtration of corrosive liquids with suction. A strongly alkaline or acid suspension is best filtered through a sintered glass funnel. Alternatively, glass wool or asbestos may be plugged into the stem of a glass funnel or supported upon a Witt plate in a glass funnel. 

If suction is to be employed, a platinum cone must be used to support the tip of the filter paper or a Witte plate or a Buchner funnel may be used with a paper that just fits the flat, perforated surface. 

Drain the crystals on a bare Witte plate or a Buchner funnel, wash them once or twice with small portions of cold water, and spread them to dry on clean filter paper supported on a glass plate. A second and third crop should be secured from the mother liquor. 

Filter the solution through a folded filter and set it aside in a quiet place to crystallize. The crystals are glassy in appearance and should not be too large or grown together. Drain them on a Witte plate and evaporate the mother liquor for a second crop. They may be obtained as needles as lath-shaped crystals or in a compact, many-sided form. The last named is the most desirable form, and conditions should be varied to avoid supersaturation (Exercise 6) until such crystals are obtained. Meanwhile, prepare some effloresced sodium sulfate by gently warming about 100 g. of the crude crystals until they fall into white powder. Place this powder in the bottom of an empty desiccator and... 

Pour the hot solution into at least 21. of cold water to which a few grams of sodium sulfite has been added and allow the white crystalline powder to settle. The water should contain a little sodium sulfite or sulfur dioxide, which will tend to prevent oxidation. Wash the precipitate several times by decantation, the wash water in each case containing sulfur dioxide and made acid with hydrochloric acid. Finally, collect the precipitate on a small Witte plate provided with a close-fitting filter paper, washing it on to the plate with portions of the filtrate and taking care not to let all the liquid drain through the filter, exposing the moist compound to the air. 

Obtain two funnels the rims of which are of just the same size. Provide one of them with a stopper which fits your filter flask and also with a Witte plate. Attach the calcium chloride drying tube to the stem of the other. / a Provide also a piece of rubber tape such as / is used to wrap joints in electrical wires and... 

When well-formed individual crystals have been obtained, filter them on a Witte plate, wash once with dilute nitric acid (1 3), pump as dry as possible, place the moist crystals in a suitable vessel, and put this in a desiccator over sulfuric acid. Watch the crystals carefully, with occasional stirring, and bottle them at once when they are dry. Do not touch them with the fingers, as this will discolor them. If they are allowed to overdry in the desiccator, they lose both crystal water and nitric acid and turn into a sticky mass of brownish-colored basic salt, which will not take up water from the air to reverse the reaction. Consequently, effloresced crystals cannot be used to complete the drying of the moist crystals. If the crystals are exposed to moist air, they deliquesce, undergo hydrolysis in the resulting solution, and form a basic salt. If they are bottled before they are dry, they will in time become discolored. If properly prepared, they will remain perfectly transparent and have a very pretty amethyst color, the intensity of which depends upon the size of the crystals. Crystals of iron alum have the same color. 

Powder very finely 20 g. of antimony oxide, Sb2C>3 (or metallic antimony), and add this in small portions at a time to 250 cc. of hot concentrated sulfuric acid contained in an evaporating dish. Maintain the heat until all of the powder has been dissolved, if necessary adding a little more acid to keep the white sulfate in solution. Allow the solution to cool and filter off the fine crystals on a platinum cone or a Witte plate with very small holes, pumping them as dry as possible. Spread the pasty mass on pieces of unglazed dishes, putting one such piece on top of another, to make a pile that consists of alternate layers of plate and sulfate. Put the entire pile in a desiccator so as to prevent absorption of moisture from the air. If the sulfate is rather wet, it may be necessary to scrape it off the plates and repeat the operation with fresh ones. Finally, spread... 

Method I.—Intimately mix 36 g. of antimony sulfide (or powdered stibnite), Sb2S3 43 g. of anhydrous sodium sulfate and 16 g. of fine charcoal in a clay crucible, which should be about half filled with the mixture. Cover with a little charcoal and heat in the furnace to quiet fusion and then for 10 min. longer. Pour out on sheet iron or on a large iron pan. Powder the cold melt and boil it half an hour with 7 g. of sulfur and 300 cc. of water. Filter, add a little sodium hydroxide, and evaporate to crystallization in a porcelain dish. Because of hydrolysis, the crystals cannot be washed with water. Collect on glass wool or on a bare Witte plate and wash with alcohol containing a little sodium hydroxide. Obtain several crops of crystals. Finally,... 

Hydroxylamine begins to crystallize in large white flakes at 0°C. Cooling below — 10°C. seems to produce only a trivial increase in the yield. The crystals produced in this fashion are collected quickly upon a filter (Witt plate), washed with cold ether, and placed in a desiccator for 15 minutes to remove the adhering solvents. If the hydroxylamine is not to be used at once, it should be placed in a stoppered tube in an ice chest. Yield 21.0 g. (63.5 per cent of theory). 

Filter pump, flask and Witt plate. Lithia bottles. 

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