Witt plate

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. 

Witterungs-bestandigkeit, /. resistance to weathering, -einfiuss, m. atmospheric in fluence. -kunde, -lehre, /. meteorology, schutz, m. protection against weather, -ver-haltnl se, n.pl. atmospheric conditions. Wittsche Scheibe. Witt plate. 

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. 

Crystals are usually washed on a bare Witte plate or Buchner funnel, using a paper on the plate only when necessary. 

When the solution is quite cold, bring the crystals on to a bare Witte plate or Buchner funnel, using a portion of the filtrate to wash them out of the beaker. Pump off the mother liquor with a water pump, washing the crystals with one or two portions of cold water. Combine the filtrate from the crystals with the wash water and evaporate the solution for another crop of crystals. Boil the solution until a rather persistent ring of solid salt tends to form at the line where the surface of the solution touches the evaporating dish then set the dish aside to cool. The second crop of crystals may be added to the first, and the two dried together. 

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... 

When satisfactory crystals have been obtained, bring them quickly upon a Witte plate, washing them on with the mother liquor. Wash the crystals with successive small portions of concentrated hydrochloric acid, being careful that none escapes the washing. Pump off the liquid each time, then spread the crystals upon absorbent paper, press them lightly with a wad of absorbent paper, and transfer them to a desiccator over sulfuric acid. As soon as they are dry, put them in a perfectly dry bottle and seal with paraffin, since they are deliquescent. They should be bright green in color and not at all yellow. It is very hard to get a perfect specimen, but it can be done, and, when successful, the specimen will keep indefinitely. 

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... 

Shake the flask containing the crystals until any cake that may have formed is broken up and quickly pour the contents of the flask onto the Witte plate. Place the second funnel rim to rim with the first as a cover and bind the rubber tape around the joint to hold the two together by an airtight joint. Pump off the mother liquor and continue to pump air through the flask until... 

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... 

Dissolve about 10 g. of commercial beryllium hydroxide or carbonate in acetic acid and evaporate to dryness on the hot plate. Dissolve the dry residue in boiling glacial acetic acid and set aside for crystallization. The salt is deposited in small colorless octahedra. These should be drained on a Witte plate and dried on paper. The salt is decomposed by wat er. 

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,... 

After some hours standing—best until the next morning—the test tube is heated on a water bath, and the liquid is distilled off. If the distillate contains free chlorine, a little mercury is added and shaken with the liquid, which is then redistilled after filtration through a dry asbestos mat on a Witte plate. The final distillation should take place from a flask furnished with a thermometer, and the liquid should boil at 69.5°. It should be preserved in a sealed tube. The camphor may be used indefinitely, as it takes part in a cycle of reactions and is left at the end of the reaction in very nearly its original state. 

Willgerodt reaction, 923, 924J, 925, Kindler modification of, 923 Williamson synthesis, 309, 665, 670, 671 Witt plate, 51... 

Another convenient device for rapid filtration is to use a large Witt plate in a steam funnel attached to a suction flask. 

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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