Liquid filtration plating solutions

The resistance of the filter plate is negligible. The problem is to determine the filtration, washing and drying times, the cake thickness, the volumes of filtrate, washing liquid and drying air. The solution to this design case is outlined below in steps. 

The cooled melt is gradually mixed with 500 g. of crushed ice, the liquid thus obtained is filtered and 120 g. of nitric acid (d. 1-4) are added to the brown filtrate, which is then heated at 50° for half an hour. After the solution has stood for twelve hours at ordinary temperature, the greater part of the dinitronaphtholsulphonic acid produced will have separated. It is filtered off and crystallises from hot dilute hydrochloric acid in small yellow needles which are dried first on porous plate and then in a desiccator over sulphuric acid and potassium hydroxide. Melting point 151°. Yield about 85 per cent of theoretical. 

The distillate is at once extracted with ether and the extract, after having been separated from the water, is heated on the water bath until most of the ether has distilled. The residue, which contains unchanged phenol as well as the salicylaldehyde, is now vigorously shaken in a small glass-stoppered bottle with two volumes of concentrated commercial sodium bisulphite solution. A thick paste of the bisulphite compound of the aldehyde is formed. After this paste has stood for from half an hour to one hour the bisulphite compound is separated by filtration at the pump, pressed well on the filter funnel, and washed several times, first with alcohol and finally with ether, until completely free from adherent phenol. The crystals (small plates, iridescent like mother-of-pearl) are then decomposed with dilute sulphuric acid in a small round-bottomed flask whi( h is fitted with an air condenser and gently warmed on the water bath. After the liquid thus produced has cooled, the aldehyde which separates is extracted with ether and the ethereal solution is dried with anhydrous sodium sulphate. The pure aldehyde which remains when the ether is evaporated distils at 196°. The yield amounts to 10-12 g. 

Oxalato-tetrammino-cobaltic Chloride, [Co(NH3)4(C204)]C1, is prepared by dissolving chloro-aquo-tetrammino-eobaltic chloride in an aqueous solution of oxalic acid and heating the mixture for some time. The oxalato-compound gradually crystallises from the warm solution, and the crystals are collected and washed on the filter with alcohol until the filtrate is free from chlorine and from oxalic acid. It crystallises in carmine-red six-sided plates if dissolved in concentrated sulphuric acid and concentrated hydrochloric acid is added to the liquid, it is transformed into dichloro-tetrammino-cobaltic chloride. Sodium nitrite and acetic acid convert it into dinitro-tetrammino-cobaltic chloride.1... 

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. 

Preparation of Zinc.—To obtain perfectly pure zinc is a task of some difficulty, so much so that the commercial article is never met with in a puro state, hut rather with variable quantities of arsenic, cadmium, tin, lead, manganese, iron, cobalt, and nickel. In order to obtain perfectly pure metal, the purest commercial ziuo should be dissolved in dilute sulphuric acid, filtered from any residue, and the foreign metals thrown down by Immersing plates of zinc in the liquid till no further deposit takes place. After separating the precipitated metals, which may be tin, lead, copper, cadmium, antimony, and a trace of arsenic, the solution is treated with carbonate of soda, and the carbonate of zinc, which Falls after filtration and thorough washing, Is dried, heated to redness to expel carbonic acid, mixed with charcoal or lampblack, and introduced into a crucible as represented in Fig. 23, placed in a furnace,... 

Oxidation of toluene-o-sulphonamide to saccharin. In a 600-ml beaker, mounted on an electric hot plate and provided with a mechanical stirrer, place 12 g (0.07 mol) of toluene-o-sulphonamide, 200 ml of water and 3g of pure sodium hydroxide. Stir the mixture and warm to 34-40 °C until nearly all has passed into solution (about 30 minutes). Introduce 19g (0.32 mol) of finely powdered potassium permanganate in small portions at intervals of 10-15 minutes into the well-stirred liquid. At first the permanganate is rapidly reduced, but towards the end of the reaction complete reduction of the permanganate is not attained. The addition occupies 4 hours. Continue the stirring for a further 2-3 hours, and then allow the mixture to stand overnight. Filter off the precipitated manganese dioxide at the pump and decolourise the filtrate by the addition of a little sodium metabisulphite solution. Exactly neutralise the solution with dilute hydrochloric acid (use methyl orange or methyl red as external indicator). Filter off any o-sulphonamidobenzoic acid (and/or toluene-o-sulphonamide) which separates at this point. Treat the filtrate with concentrated hydrochloric acid until the precipitation of the saccharin is complete. Cool, filter at the pump and wash with a little cold water. Recrystallise from hot water. The yield of pure saccharin, m.p. 228 °C, is 7.5 g (58%). 

The principle of operation for a cross-flow filtration system is to recirculate a liquid solution or suspension, usually using a positive displacement pump, through the membrane module, which may be arranged as multiple tubes, a spiral wound sheet or in a plate and frame configuration. The use of... 

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