Drying adhering liquid

Although the crystals are likely to be pure, the mass of crystals will retain some liquid when the solid crystals are separated from the residual liquid. If the adhering liquid is dried on the crystals, this will contaminate the product. In practice, the crystals will be separated from the residual liquid by filtration or centrifuging. Large uniform crystals separated from a low-viscosity liquid will retain the smallest proportion of liquid. Nonuniform crystals separated from a viscous liquid will retain a higher proportion of liquid. It is common practice to wash the crystals in the filter or centrifuge. This might be with fresh solvent, or in the case of melt crystallization, with a portion of melted product. 

After re-cooling to 70°C with dry ice, the wash solvent is completely decanted and any residual adhering liquid is removed from the product by evacuating the flask for several hours, first at room temperature and then at 100°C. 

Ordinary varnishes are more or less dense liquids which, when spread on the surface of an object, leave, after a longer or shorter time, a dry, adherent, smooth layer with a continuous, shining surface, which is unaltered by the air or moisture. 

The cell windows should be maintained clean with no scratches and adhering liquids. The placement of the cuvettes is very important. Otherwise, cell walls can block the radiation beam, resulting in irreproducible erroneous results. Cells should always be stored in matched pairs, dry, and preferably inside a protective container. Catalogs provide figures and a list of the different types of cells available commercially. 

On drying, the liquid adheres as a uniform solid film on the surface. 

The reversible potentials for both compounds obtained under wet conditions ([C4mpyr][N(Tf)2], [H2O] 0.13 M) are very similar to those obtained in extensively dried ionic liquid. For these compounds, it may be concluded that the voltammetry of adhered microparticles provides an efficient and convenient method for obtaining water-free reversible potentials for water-sensitive reduction processes in ionic liquids under bench top conditions, without the need to use extensively dried ionic liquids or operate under more cumbersome dry box or vacuum line conditions. 

Three phases of the drying process are distinguished I, II, and III. In phases I and II, the mother liquor, first as bulk and second as adhering liquid, is evaporated. This evaporation occurs at the temperature and pressure close to the equilibrium vapor pressure of the mother phase (see Figure 14.8). 

Figure 14.8 Schematic representation of the liquids evaporated, dried in the d ing phases l-lll. In phases I and II, surrounding and adhering liquid is removed via evaporation.

The air-dried material was extracted 3 times in water over a boiling water bath for about 30 min. The resulting extract was poured off and the residual plant material freed from adherent liquid in a press. The combined extracts were then precipitated with basic lead acetate and filtered. The filtrate, after removal of Pb by HjS04, was treated with Ba(OH)j to remove SO, and was concentrated under reduced pressure. The solution was then precipitated by mercuric acetate, and the resulting Hg salt, after washing, was decomposed with HjS, filtered from HgS, and evaporated to dryness in a vacuum. 

The technique used to study dewetting dynamics on materials consists of making a flat, smooth elastomer surface. A hquid puddle is deposited within a 50-mm-diameter ring of 0.1-mm-thick plasticized adhesive paper adhering to the substrate. The adhesive paper acts as a spacer. A microscope slide is drawn over the liquid to obtain a liquid film of ca. 0.1-mm thickness. At this thickness, the liquid film is unstable, being much less than the equilibrium value, of ca. 1.5 mm calculated from Eq. (29). Nucleation of dry patches... 

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. 

---