Stirred Settling

Samples containing >10% crude fat must be defatted before analysis with petroleum spirit (light petroleum, 40-60°C boiling range). This may be done either in a Soxhiet extractor, or in a beaker by stirring, settling and decanting three times with 30 ml petroleum spirit. Allow the fat-free sample to air-dry in a fume cupboard. 

Aggregation of Particles. Sinclair 91) discusses the coagulation in a homogeneous aerosol. For ordinary concentrations of aerosols the coagulation rate is low. Stirred settling of the aerosol produces faster rates. Equations applicable to these processes are given. 

Kinetics (Cord.) of centrifugation, 115-117 of cyclones, 117-120 electrostatic controlled (see Electrostatic controlled kinetics) equation of motion, 76-77 without external forces, 77-80 ideal stirred settling, 86-88 impaction (see Impaction) isokinetic sampling, 120-124 limitations on, 84 one-dimensional motion, 84-86 respirable sampling, 124-128 stop distance, 83... 

In air-cleaning electrostatic precipitators, the flow is turbulent and the collection situation is analogous to stirred settling, as described in Section 3.8. Consider the wire-and-tube geometry shown in cross section in Fig. 15.7. In a period dt that is brief compared with that required for turbulent mixing, all particles within a distance V- dt of the tube wall will be removed. For simplicity, we assume that par-... 

Cautiously add 250 g. (136 ml.) of concentrated sulphuric acid in a thin stream and with stirring to 400 ml. of water contained in a 1 litre bolt-head or three-necked flask, and then dissolve 150 g. of sodium nitrate in the diluted acid. Cool in a bath of ice or iced water. Melt 94 g. of phenol with 20 ml. of water, and add this from a separatory funnel to the stirred mixture in the flask at such a rate that the temperature does not rise above 20°. Continue the stirring for a further 2 hours after all the phenol has been added. Pour oflF the mother liquid from the resinous mixture of nitro compounds. Melt the residue with 500 ml. of water, shake and allow the contents of the flask to settle. Pour oflF the wash liquor and repeat the washing at least two or three times to ensure the complete removal of any residual acid. Steam distil the mixture (Fig. II, 40, 1 or Fig. II, 41, 1) until no more o-nitrophenol passes over if the latter tends to solidify in the condenser, turn oflF the cooling water temporarily. Collect the distillate in cold water, filter at the pump, and drain thoroughly. Dry upon filter paper in the air. The yield of o-nitrophenol, m.p. 46° (1), is 50 g. 

Add the aluminium chloride in 25 g. portions to the 1 -litre of dry nitrobenzene contained in a 2 - 5-litre round-bottomed flask stir after each addition. The temperature may rise to about 80° dming the addition -. cool the flask occasionally under running water. When all the aluminium chloride has been added, cool the solution to room temperature a little solid may settle to the bottom. 

The number of washings may be reduced to about twenty, if time is allowed for diffusion of the alkali from the surface of the catalyst into the surrounding wash water. Use 750 ml. of water in each washing, allow diffusion to proceed for 3-10 minutes, stir again, and decant the supernatant liquid as soon as the catalyst settles to the bottom. 

Prepare a solution of 41 g. of anhydrous palladium chloride (1) in 10 ml. of concentrated hydrochloric acid and 25 ml. of water (as in A). Add all at once 60 ml. of 6iV-sulphuric acid to a rapidly stirred, hot (80°) solution of 63 1 g. of A.R. crystallised barium hydroxide in 600 ml. of water contained in a 2-htre beaker. Add more 6iV-sulphuric acid to render the suspension just acid to htmus (5). Introduce the palladium chloride solution and 4 ml. of 37 per cent, formaldehyde solution into the hot mechanically stirred suspension of barium sulphate. Render the suspension slightly alkaline with 30 per cent, sodium hydroxide solution, continue the stirring for 5 minutes longer, and allow the catalyst to settle. Decant the clear supernatant hquid, replace it by water and resuspend the catalyst. Wash the catalyst by decantation 8-10 times and then collect it on a medium - porosity sintered glass funnel, wash it with five 25 ml. portions of water and suck as dry as possible. Dry the funnel and contents at 80°, powder the catalyst (48 g.), and store it in a tightly stoppered bottle. 

After 3 hours the stirring is stopped and the solution allowed to settle. By this time just about all the foil will have turned to dust, which is going to make the next step of vacuum filtration very difficult because it will plug up the filter paper in a second. So the chemist lets it settle, then pours off the liquid through the vacuum filtration setup (see methodology section). The flask is rinsed with lOOmL methanol, the methanol poured through the grey filter cake and the filter cake discarded. All of the filtrate is placed in a flask and vacuum distilled to remove all the methanol, isopropyl alcohol and water which will leave the chemist with oil and junk in the bottom of the flask. 

Since the formamide reaction solution is going to be a lot cleaner than the tarry mess of the original recipe, the chemist has yet another option to explore. Instead of hydrolyzing in the reaction pot, the chemist can add SOOmL of clean dHjO and stir just like in the crappy original method except that this time the chemist is going to look for a heavy oil layer that will settle at the bottom. The up-... 

In contrast to the reaction with lithium amide, the sodium amide suspension immediately settles out after stopping the stirring and the supernatant ammonia has a grey or black colour, due to colloidal iron. In some cases it took a long time before all of the sodium had been converted (note 4). A further 0.1 g of iron(III) nitrate was then added to accelerate the reaction and some liquid ammonia was introduced to compensate for the losses due to evaporation. 

In the case of thickeners, the process of compaction of the flocculated material is important. The floes settle to the bottom and gradually coalesce under the weight of the material on top of them. As the bed of flocculated material compacts, water is released. Usually the bed is slowly stirred with a rotating rake to release trapped water. The concentrated slurry, called the underflow, is pumped out the bottom. Compaction can often be promoted by mixing coarse material with the substrate because it creates channels for the upward flow of water as it falls through the bed of flocculated material. The amount of compaction is critical in terms of calculating the size of the thickener needed for a particular operation. The process of compaction has been extensively reviewed in the Hterature (41,42). 

Orthokinetic flocculation is induced by the motion of the Hquid obtained, for example, by paddle stirring or any other means that produces shear within the suspension. Orthokinetic flocculation leads to exponential growth which is a function of shear rate and particle concentration. Large-scale one-pass clarifiers used in water installations employ orthokinetic flocculators before introducing the suspension into the settling tank (see Water,... 

The design of the sludge-blanket clarifiers used primarily in the water industry is based on the jar test and a simple measurement of the blanket expansion and settling rate (12). Different versions of the jar test exist, but essentially it consists of a bank of stirred beakers used as a series flocculator to optimize the flocculant addition that produces the maximum floc-setfling rate. Visual floc-size evaluation is usually included. 

When boric acid is made from colemanite, the ore is ground to a fine powder and stirred vigorously with diluted mother Hquor and sulfuric acid at about 90°C. The by-product calcium sulfate [7778-18-9] is removed by settling and filtration, and the boric acid is crystallised by cooling the filtrate. 

Batch-stirred vessels are most often used in treating material with powdered activated carbon (72). The type of carbon, contact time, and amount of carbon vary with the desired degree of purification. The efficiency of activated carbon may be improved by applying continuous, countercurrent carbon—Hquid flow with multiple stages (Fig. 3). Carbon is separated from the Hquid at each stage by settling or filtration. Filter aids such as diatomaceous earth are sometimes used to improve filtration. 

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