On Distilled Waters

A simple ealibration eurve based on distilled water is suitable for tungsten determination (linearity range is 1-50 mg/dm of W), no interferenee from Fe, Co, Cr, Ni was found. The aeeuraey of the method is eonfirmedby analysis of eertified referenee materials of high alloy steels and niekel based alloys (in range of 0.3 to 15 % W). The analyzed values are agreeing well with the eertified values. 

The accuracy of the method was tested experimentally by running duplicate titrations on distilled water, artificial seawater with and without sulfate, and artificial Dead Sea waters. For each run, alkalinity was calculated by two methods ... 

Figure 34. Surface pressure - area isotherms for monolayers of Ci 8TCNQ (a), the mixture of the dihydrothiophene and G 8TCNQ (b), and the complex (c), spread on distilled water, as compared with that on the aqueous subphase with 10 5M LiTCNQ (c ).

The monolayer behavior of A-stearoyltyrosine (Fig. 16) was more complex. Under conditions (0.0liV HCl, 22 C) where the racemic material formed a condensed film having a limiting molecular area of 39 2 A, the force-area curve of L-(+)-A-stearoyltyrosine exhibited a liquid-expanded film at large areas (ca. 100-45 per molecule) followed by a transition beginning at 16.5 dynes/cm surface pressure to a condensed phase having a smaller limiting molecular area of 34 2 A . However, both these latter samples exhibited only the liquid-expanded phase on distilled water alone. 

Figure 1. Effect of pH on surface pressure of a BSA monolayer spread on distilled water subsequently injected with SDS...

Wash away any salts in the preparation by floating the grid, specimen side down, on distilled water. 

Float the grids with the sectioned cells for 10 min on distilled water... 

The clearest results were obtained with the normal, saturated fatty acids and alcohols. These formed stable films, which would stand considerable compression laterally, and (at room temperature on distilled water) gave a very clearly marked critical area at which the surface pressure first appeared, this point being of course Pockels s critical point of the first diminution of surface tension. As the area was reduced from large initial areas no surface pressure could be detected until the area had reached about 22 sq. A. per molecule and at 20 5 sq. A. the pressure increased very rapidly indeed with further increase of pressure. The curve I of Fig. 15 shows the relation between surface pressure and area per molecule, which is obtained with accurate apparatus for the fatty acids on water curve III is that obtained with the alcohols.3... 

With the fatty acids on distilled water the very steep curve I continues almost down to zero pressure. On dilute acid solutions, however, this steep curve only occurs above about 17 dynes per cm., and below this pressure there is a second, nearly straight portion of the curve (see curve III), cutting the abscissa at about 25 sq. A. Both the upper and lower parts of these curves are very little changed when the number of carbon atoms in the acid is altered from 14 to 22 carbon atoms the steep curve always tends to an area within 1 sq. A. of 20 5 the lower part on acid solutions tends to 25 sq. A. for the medium-chain aoids, about 16 carbons, and to very slightly smaller areas for longer chain acids (24 for the 22... 

Float the nitrocellulose filter on distilled water until evenly wet, and then place in a filter holder. Wash with cold 6X SSC using about 3 ml/cm2 of filter and a flow rate of 0.2 ml/cm2/min. 

Two types of samples were prepared for detailed morphological examination. Sections of the as-polymerized material were examined directly by WAXS and DSC. Samples also were prepared by casting films from a solution of the polymer in dimethyl formamide (DMF) at 52°C. Solvent was allowed to slowly evaporate, and the films were dried by annealing for 670 hr at 52°C, followed by slow cooling to room temperature. Thin films suitable for electron microscopy were cast from 0.5 wt % polymer in DMF onto clean glass slides, and after 20 hr of annealing at 52°C, floated off on distilled water and mounted on 300-mesh copper grids. 

The spot-test technique is as follows. Place a drop of the test solution on a spot plate and add 1-2 drops of the reagent. It is essential that the solution be strongly alkaline the addition of 1 drop of 2m sodium hydroxide may be advisable. According to the concentration of magnesium a blue precipitate is formed or the reddish-violent reagent assumes a blue colour. A comparative test on distilled water should be carried out. 

The nature of the adsorbed monolayer depends on the interaction of the polar head group and the substrate surface. For example, if a glass microscope slide is raised up through a barium stearate monolayer spread on distilled water, the molecules in the film will be oriented with the hydrocarbon chains outwards, and hence the adsorbed film is hydrophobic 1I80. When a previously coated plate is dipped back into the surfactant-coated water, a second oriented layer will be deposited and the coated surfac m ain becomes hydrophilic as the head groups point outward. 

Chlorides were determined by potentiometric titrations performed on distilled water dilutions. Carbonates and bicarbonates were either determined by titration or by calculation from pH measurements. Sulfates were determined by the gravimetric method utilizing BaS04 precipitation. 

Figure 3. Surface pressure (P) and surface potential (V) vs. area for (a) poly(i.-leucine), (b) poly(i -methione), (c) poly(i.-norleucine) on distilled water...

Fig. 3. Plots of log (N,/Nb) vs II for protein monolayers O, BSA on 25% ammonium sulfate solution at 25°C , pepsin on distilled water at 20°C. From data of MacRitchie (1963).

Fig. 5. II — A curve of bovine serum albumin on distilled water at 20°C. Curve on left is equilibrium curve, assuming no desorption. Curve on right is dynamic curve, which would be obtained if no expulsion of segments from interface occurred. From MacRitchie (1977a), reproduced with permission.

Many topicals require the addition of water to prepare their use dilution, but product labels often do not clearly specify the type of water to be used for this purpose. Normally, one would use tap water for this purpose, but label claims for germicidal activity may be based on distilled water as the product diluent. Current regulations in the United States assume that distilled water is used and do not require that this be stated on the label. Consumers are usually unaware of the need to use distilled water. 

Mohammed et al. (144, 145), in a series of studies, examined several aspects of emulsion films with and without demulsifiers as well as their chemistries. Using the Langmuir balance for studying the air/ crude/water interface, they examined the sinface pressme n-area isotherm for monolayers of Buchan crude s asphaltenes and resins and their mixtures, spread on distilled water at pH 6.2 and 25°C. They found that the asphaltenes upon compression formed solid films, that could withstand pressures up to 45 mN m" in contrast to the resin films at 7 mN m which thereafter collapsed. The asphaltenes formed highly stable emulsions in contrast to the resins alone, which formed the least stable emulsions. They found that film compressibility and emulsion stability decreased as resin content increased. Temperature increases caused no significant effects on asphaltene monolayer compressibility as was observed earlier by Reis-berg and Doscher (126) for natural crude oil films. 

FIGURE 8.16. A monomolecular film of a straight chain carboxylic acid such as myristic acid on distilled water will show a sharp transition in the n-A curve as the head groups become more closely packed. That kind of transition may be viewed as something like a reversed sublimation in which the film passes from gaseous to solid condensed without passing through the liquid expanded state. With very careful experimental work, it is sometimes possible to identify an intermediate liquid expanded phase as illustrated for myristic acid on 0.1 N HCl. 

Le Menitre 49250, Beaufort en vallee, France) were sown on distilled water either in the dark or under continuous standard far-red light as described elsewhere (1). 

Calibration in HSGC is profoundly influenced by parameters which may alter either pt or 7/. That the equilibration temperature plays an important role has already been stressed, but 7 is also altered if the composition of the mixture to be analysed changes. In other words, 7/ is influenced by the concentration of other substances present. This means that simple binary solutions cannot be used for calibration purposes. A good example to illustrate this point is the determination of halogenated pollutants in sea water. Calibration with use of solutions based on distilled water can give rise... 

This demonstration procedure should be performed on distilled water (where no interferences should be present) and then on matrix samples (dialysis water, urine, and/or blood) to evaluate the weight of matrix effect on the reliability of the method. 

Procedure. A drop of the test solution is treated on a spot plate with 1 or 2 drops of the alkaline dyestuff solution. According to the magnesium content, a blue precipitate is formed, or there is a color change from red-violet to blue. It is always necessary to be sure that sufficient alkali is present if the solution is too acid, the yellow of the free dyestuff appears, and a few drops of strong alkali should be added. If only traces of magnesium are to be detected, a comparative test on distilled water is necessary. 

If fi > 0 and 5 < 0, then an oil drop will form a lens, which may be in equilibrium with the original air-foaming liquid surface (i.e., partial wetting) or that surface after incorporation of material from the oil drop (i.e., pseudo-partial wetting). However, formation of oil lenses on the equilibrium liquid surface does not preclude the possibility that the initial spreading coefficient S is positive. If 5 > 0 and S < 0, then pseudo-partial wetting will occur and the oil drop may, for example, spread to form a duplex film, which is, however, unstable. That film will disproportionate to form oil lenses in equilibrium with oil-contaminated air-water surfaces The spreading of a drop of benzene on distilled water to form lenses in equilibrium with a benzene monolayer exemplifies this type of behavior. 

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