Bottom creaming

Figure 3.27 Breakdown mechanisms of emulsions (from top to bottom creaming, coalescence, flocculation and Ostwald ripening).

Heavy solvents (high specific gravity) are undesirable in most cases because it is hard to stabilize the emulsion when the EC is mixed with water. If the specific gravity of the solvent is near that of water, the setting tendency of the emulsion is decreased. The terms top creaming and bottom creaming are used to describe emulsions in which the insecticide-containing solvent has risen to the top or settled to the bottom of the emulsion. Other... 

Figure Bl.14.13. Derivation of the droplet size distribution in a cream layer of a decane/water emulsion from PGSE data. The inset shows the signal attenuation as a fiinction of the gradient strength for diflfiision weighting recorded at each position (top trace = bottom of cream). A Stokes-based velocity model (solid lines) was fitted to the experimental data (solid circles). The curious horizontal trace in the centre of the plot is due to partial volume filling at the water/cream interface. The droplet size distribution of the emulsion was calculated as a fiinction of height from these NMR data. The most intense narrowest distribution occurs at the base of the cream and the curves proceed logically up tlirough the cream in steps of 0.041 cm. It is concluded from these data that the biggest droplets are found at the top and the smallest at the bottom of tlie cream.

Hydrolysis of methyl m-nitrobenzoate to m-nitrobenzoic acid. Place 90 -5 g. of methyl m-nitrobenzoate and a solution of 40 g. of sodium hydroxide in 160 ml. of water in a 1-htre round-bottomed flask equipped with a reflux condenser. Heat the mixture to boiling during 5-10 minutes or until the ester has disappeared. Dilute the reaction mixture with an equal volume of water. When cold pour the diluted reaction product, with vigorous stirring, into 125 ml. of concentrated hydrochloric acid. Allow to cool to room temperature, filter the crude acid at the pump and wash it with a httle water. Upon drying at 100°, the crude m-nitrobenzoic acid, which has a pale brownish colour, weighs 80 g. and melts at 140°, Recrystalhsation from 1 per cent, hydrochloric acid afibrds the pure acid, m.p. 141°, as a pale cream sohd the loss of material is about 5 per cent. 

Cyclopropyltriphenylphosphonium Bromide (5). The lactone salt is pyrolyzed by placing it in a round-bottom flask fitted with an adaptor attached to a vacuum source (aspirator is sufficient). The flask is heated (oil bath) to 180-190° for 48 hours. The residue is a virtual quantitative yield of the tan product, which may be crystallized from ethyl acetate giving cream crystals, mp 189-190°. An alternate setup is convenient if a drying pistol (Abderhalden) is available. The compound is placed in the pistol, which is then evacuated. Decalin (bp approx. 187°) is refluxed over the pistol to provide the heating source. The work-up is the same. 

With the bit directly on bottom, start the air down the hole. Straight air should be pumped at normal drilling volumes until the surfactant sweep comes to the surface, appearing at the end of the blooey line and foaming like shave cream. 

Figure 15.6 Influence of solid pigments on the NIR absorbance spectra of coiored poiypropyiene carpets. Note that as the carpets change from dark biue (bottom trace) to cream coior (top trace) the baseiine shift increases, the baseiine tiit increases, and the intensity of the absorbance peaks decreases. Reprinted with permission from Rodgers (2002). ...

Another technique consists of submitting the emulsion to centrifugation and determining the droplet volume fraction < / at the top (bottom) of the cream (sediment). The centrifugation typically takes several hours until the equilibrium volume fraction is achieved. After equilibration, if the droplets occupy a distance much less than that of the centrifuge lever arm, the spatial gradient in the acceleration can be neglected, and the osmotic pressure can be determined (see Fig. 4.1) ... 

Bis(dimethyl hydrogen phosphite-/ )bis(dimethyl phosphito-P)platinum(lI) (0.420 g, 0.66 mmole) and c/s-[dichlorobis(triphenylphosphine)platinum(ll)] (0.524 g, 0.66 mmole) are refluxed in toluene (25 mL) for 30 hours. The colorless reaction mixture is filtered while hot using vacuum to remove any unreacted c/s-[dichlorobis(triphenylphosphine)platinum(Il)]. The filtrate is transferred to a 100-mL, round-bottomed flask and evaporated to dryness on a rotary evaporator, using gentle heating if necessary. The cream-colored residue is dissolved in a mixture of dichloromethane (15 mL) and methanol (15 mL) and the solution is allowed to concentrate slowly under water aspirator vacuum on a rotary... 

Return the mixture to the saucepan. Cook over low heat, stirring and scraping the bottom of the pan with a wooden spoon or a heat-resistant rubber spatula, until the mixture is thick enough to coat the spoon. Immediately remove from the heat and strain through a fine-mesh sieve into a bowl with the heavy cream. Chill thoroughly. 

The pressure drop and pumping requirements are functions of the type of flow and of the rheological properties of the dispersion. If the flow rate in a pipeline falls below the critical deposit velocity then particles or emulsion droplets will either sediment or cream to form a layer on the bottom or top wall, respectively, of the pipe. Some correlations that have been developed for the prediction of critical deposit velocity are discussed by Nasr-El-Din [86] and Shook et al. [90]. 

In a small heavy-bottomed saucepan, stir together the sugar, cream of tartar, and V3 cup water, and bring to a boil over high heat. 

Fill the pastry bagwith buttercream. One at a time, turn the cakes over and starting at one end, insert the piping tip almost an inch deep and insert a bit of cream. Do this every V2 inch. You should end up with 3 or 4 holes in the bottom of each Goldie where you ve inserted the buttercream. (My motto is "A bite of cream in every bite ) When all the Goldies are filled, cover them with plastic wrap and chill in the refrigerator for at least 15 minutes. 

To assemble, slice the cooled shortcakes in half and arrange them on individual plates. Spoon V4 cup or more of the strawberry-mint mixture onto the shortcake bottoms, and finish with a dollop of Vanilla Whipped Cream. Place the other halves of the shortcakes on top and devour ... 

A hand cream appears smooth and uniform after you prepared it, but in a week of storage most of the water settles on the bottom and most of the oil separates on the top. What do you think may have gone wrong with the hand cream preparation ... 

Lachman would limit the fermentors to 5000 gallons, wisely we think because of the lack of cooling facilities. Production of piquette (pomace wine for distilling) is described. It should have at least 5-7 percent alcohol. Extraction with water passed from the bottom of one tank to the top of the next was used. The washed pomace was still worth 0.75- 1.25 per ton for cream of tartar production. 

Figure. 5.2. Principle of operation of a centrifugal milk separator. Milk enters at the bottom of the unit and separates into heavier shim (dark grey) and lighter cream (pale grey) fractions which are recovered at the top of the separator (Reproduced with permission from Dairy Processing Handbook, Tetra Pak Processing Systems AB, Lund, Sweden, 1995).

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