Color value change

Students will describe the concept of color value change. 

Use the concept of light wave reflection to explain why color value changes when a solution is diluted. 

This is especially true in industrial and urban areas. Fig. 87 shows a paint containing Chrome Yellow, which was subjected to a test as described in Section 1.6.2.2 treatment with 1 N sulfuric acid for one hour at 70°C. The distinct color change on the circular test area is accompanied by a considerable gloss reduction. In the corresponding lead chromate-free system, it is only the binder that is affected, which reduces the gloss the color value on the other hand is retained. 

Collection should befor at least 1 h, orsay 10 times as long as is needed for the color to change from reddish-purple to blue, which occurs after about 30 yg of NaOH has been collected. Collection may have to be for as long as 3 h if the concentration of NaOH is well below the Threshold Limit Value / Time Weighted Average (TLV-TWA), viz. 2 mg/m3 of air. 

In this demonstration, color value was changed by dilution. How else can color value be changed ... 

The colorant behaves like an indicator, in that it changes color with change in pH, but unlike the usual indicators, it ordinarily changes in amount of color rather than in kind of color. The increase in color seen when the pH value is raised occurs almost instantaneously, whereas the... 

Change In total color, determined by Hunter Colorimeter, Model D25M-9. d Color value, Hunter Colorimeter, Model D25M-9. 

TAMOL dispersants have wide application in the textile industry as primary and auxiliary dispersants for dyes, pigments, or fillers to give better suspension, color value, fluidity, and grinding properties. Unlike many dispersants, these light-colored products do not change color at high temperatures or upon exposure to light and, thus, do not alter the color of dyestuffs. 

Solutions of homoserine and its lactone slowly reach equilibrium under most conditions at room temperature. As a result, samples of these derivatives prepared for analysis often gradually change in concentration even during the chromatographic steps, and color values usually reflect such losses. Acidic conditions favor lactone formation, and trifluoroacetic acid at 20°C for 1 hr can be used to convert essentially all of the homoserine (free or in peptides) to the lactone form (Ambler 1965). Alkaline conditions favor homoserine formation, but may often be too harsh for many peptide procedures (see Ambler 1965). 

In all of the examples we have studied here each of the atoms in the lattice have the same coordination number, and, if we restrict ourselves to modeling the coloring with changes in a values only, have identical third moments. This is not true of systems where the coordinaton numbers are different. 46 shows an example. We can simply show... 

FIGURE 5.18 Changes in a color values at the surface (-0-), at an intermediate position (- -), or at the centre (- -) of meat cubes after pressurization at 10°C for lOmin in air. Results are from at least six measurements on the same semimembranosus meat sample. (From Carlez, A. et ah, Lebensm. Wiss. TechnoL, 28, 528, 1995. With permission.)... 

These findings can be explained by the great tendency of the hydroxy- and amino groups to chelate with metal ions. Chelation can be observed by the occurence of several effects a drop in pH values, changes of spectra and color, change of solubility and decrease of metal ion concentration in solution ... 

Figure 10.5 compares color-coded calculated electron density at the van der Waals surfaces projected onto the van der Waals surfaces for four hydrazine radical cations, the Hab values obtained from our analysis of the cross-rates for these couples (from Table 10.4), and how these Hab value changes would affect the rate constants if only differences in Hah affected the rate constants (labeled Ar rei)- It is seen that although Ay changes are by far the most important factor in determining the 2 x lO " range in / n(fit) obtained for the couples studied, changes in Hab lead to clearly detectable effects on intrinsic rate constants. 

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