Color causes

General Methods. Traces of acetylene can be detected by passing the gas through Ilosvay s solution which contains a cuprous salt in ammoniacal solution. The presence of acetylene is indicated by a pink or red coloration caused by the formation of cuprous acetyHde, CU2C2. The same method can be used for the quantitative deterrnination of acetylene in parts per biUion concentrations the copper acetyHde is measured colorimetricaHy (87). 

The conjugated chromophore (color-causing) system can be extended by electron-donor groups such as —NH2 and —OH and by electron-acceptor groups such as —NO2 and —COOH, often used at opposite ends of the molecule. An example is the aromatic compound alizarin [72-48-0], also known since antiquity as the ted dye madder. 

Organic colors caused by this mechanism are present in most biological colorations and in the triumphs of the dye industry (see Azinedyes Azo dyes Eluorescent whitening agents Cyanine dyes Dye carriers Dyes and dye intert diates Dyes, anthraquinone Dyes, application and evaluation Dyes, natural Dyes, reactive Polymethine dyes Stilbene dyes and Xanthenedyes). Both fluorescence and phosphorescence occur widely and many organic compounds are used in tunable dye lasers such as thodamine B [81-88-9], which operates from 580 to 655 nm. 

Testing for excess of nitrous acid at the end of the reaction. For this purpose starch-potassium iodide papers are best used, and these indicate nitrite in acid solution by turning blue instantaneously. With some practice, the nitrite reaction can be clearly distinguished from the coloration caused by certain diazo compounds, such as those bearing nitro substituents. The latter react only after 0.5 to 2 seconds. Often the difference becomes more marked after dilution of the diazo solution with concentrated hydrochloric acid. A properly conducted diazotization should exhibit on completion a very weak nitrite reaction, corresponding to an excess of about 10 4 m. 

The endpoint of this oxidation is indicated by the appearance in the reaction mixture of a red-orange color caused by excess bromine. 

This aminopropanol treatment for removal of bound gossypol appeared to be an excellent means to test the role of bound gossypol in the color problem. The water and salt-solution insoluble fraction (l) of LCP flour that contained the brown color causing pigments was treated for 15 min at 80°C with 2Z... 

In most spectrophotometric analyses, it is important to prepare a reagent blank containing all reagents, but with analyte replaced by distilled water. Any absorbance of the blank is due to the color of uncomplexed ferrozine plus the color caused by the iron impurities in the reagents and glassware. Subtract the blank absorbance from the absorbance of samples and standards before doing any calculations. 

A commun means of detecting hypochlorites is the production of u blue color (caused by free iodine) with starch iodide paper by hypochlorites in weakly alkaline solution. Silver nitrate also precipitates part of the hypochlorite in solutions as white silver chloride. 

Elemental phosphorus exists in several allotropic forms (Van Wazer 1982). The best known and most important commercially is the a-white phosphorus whose properties are given in Table 3-2. Commercial white phosphorus is 99.9% pure, with a slight yellow color caused by traces of red phosphorus impurities. Hence, white phosphorus also is known as yellow phosphorus. When a-white phosphorus is cooled below -79.6°C, P-white phosphorus forms. Other important solid allotropes of phosphorus are red and black phosphorus (Van Wazer 1982). 

Yellowish white precipitate of iron (III) phosphate Reddish brown coloration caused by complex formation Reddish brown precipitate formed in the presence of hydrochloric acid... 

Immediately upon connecting the cell to a source of direct current, a deposit of gray metallic zinc appears on the surface of the cathode and bubbles of chlorine gas appear at the surface of the anode. A simple chemical test for chlorine may be made by leading this gas into an aqueous sodium iodide solution, whereupon the solution assumes a yellow color caused by displacement of iodine by chlorine. Accordingly, it is concluded that the products of the electrolysis of a zinc chloride solution are elemental zinc and elemental chlorine, and the next problem is that of explaining the mechanism by which these products may be produced. 

Figure 6.2 Fading of hair color caused by 6 months of exposure to sunlight at the ground surface in a temperate environment faded upper surface (a) lower surface shows original brown coloration (b) transverse section showing histological alteration to the uppermost margin of the hair fiber (c bar equals 10pm).

Fritsch, E. Rossman, G. R. (1988b) An update on color in gems. Part 3 Colors caused by band gaps and physical phenomena. Gems Gemol., 24, 81—102. 

Some potential applications of enzymes that have been identified for the improvement of waste quality include the transformation of toxic and color-causing aromatic compounds, cyanide, pesticides, surfactants, and heavy metals. In addition, some physical modifications in waste characteristics have been achieved through the mixing of solid wastes with enzymes. These applications are summarized in Table 1, and some promising applications are described in the following. 

For qualitative identification, the Rf values are calculated from the distances measured on the plate or paper. Alternatively, the distances migrated can be measured relative to a standard run on the same plate, which usually is more reproducible. The colors caused by the visualizing reagents can also be used for identification sometimes. 

Identification Transfer 1 g of sample and 1 g of potassium metabisulfite to a 100-mL volumetric flask, dissolve in about 50 mL of pH 3.0 Citrate-Citric Acid Buffer (see Assay, below), and dilute to volume with the same buffer. The red color caused by anthocyanins is bleached. 

A library obtained in this way can then be examined with regard to its interaction with a receptor. It is challenging to find an easy way to identify substances which are capable of interacting with the receptor. If a binding interaction takes place, the identification of the responsible structure can be carried out as follows the receptor is labeled with a dye molecule so that an interaction can be detected optically by a change in color caused by the substrate-receptor complex. Finally, the structure of an active molecule can be deduced from the label to which it is correlated. 

Ghiradella H, Aneshansley D, Eisner T et al (1973) Ultraviolet reflection of a male butterfly interference color caused by thin-layer elaboration of wing scales. Science 179(4071) 415... 

The presence of unsymmetrical dialkyl ditcllurium and unsymmetrical diaryl ditellurium" compounds in solution was confirmed by Te-NMR spectroscopy H-NMR spectroscopy , and mass spectroscopy . Cyclohexyl methyl ditellurium was claimed to have been isolated from a reaction mixture obtained by sequential addition of cyclohexyl bromide and methyl iodide to a solution of tetratelluride anions in dimethylformamide . The chromophoric Te —Te group in the aliphatic and aromatic ditellurium compounds imparts a characteristic orange to red color caused by an absorption maximum at approximately 400 nm. Most of the aromatic ditellurium derivatives are stable as solids toward atmospheric agents, but oxidize slowly when dissolved. The short-chain aliphatic ditellurium compounds are distillable red liquids having an obnoxious odor that clings to skin and clothes. Ditellurium compounds with more than ten carbon atoms in each aliphatic group are low melting solids that can be handled in air. 

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