Reagents discolored

The acid is rather slow to react with aUphatic hydrocarbons unless a double bond or other reactive group is present. This permits straight-chain fatty alcohols such as lauryl alcohol [112-53-8] C22H2 0, to be converted to the corresponding sulfate without the degradation or discoloration experienced with the more vigorous reagent sulfur trioxide. This is important in shampoo base manufacture (see Hairpreparations). 

Note Sulfuric acid (4%) can also be employed in place of hydrochloric acid [3]. If ammoniacal mobile phases are employed the ammonia should be removed completely (e.g. heat to 105 °C for 10 min) before dipping or spraying otherwise background discoloration can occur. The addition of titanium(III) chloride to the reagent allows also the staining of aromatic nitro compounds [6]. 

Note Traces of ammonia from the mobile phase should be removed from the plate completely to avoid background discoloration (grey veil) [1]. If the layer is sprayed too heavily the initially grey-black chromatogram zones can fade again [2]. The reagent which is usually employed as a 1 to 2% solution [2, 3, 6, 7] can be treated with a few drops of nitric acid to clarify the solution [2]. 

The metal lost from the inside of pumps, reaction vessels, pipework, etc. usually contaminates the product. The implications of this depend upon the product. Ppb levels of iron can discolor white plastics, though at this level the effect is purely cosmetic. Ppm levels of iron and other metals affect the taste of beer. Products sold to compositional requirements (such as reagent-grade acids) can be spoiled by metal pick-up. Pharmaceutical products for human use are often white tablets or powders and are easily discolored by slight contamination by corrosion products. 

If the temperature is allowed to rise much above 5°, charring results and the product is discolored. A Dry Ice bath may be used to advantage. The reagent thus prepared should be used within a few hours, since dioxane is slowly attacked by sulfur trioxide. 

Urea—formaldehyde and melamine—formaldehyde reagents are resin formers, which not only cross-link cotton but also copolymerize with themselves. These have been used both as simple cross-linkers or prepolymer systems. If too much of the polymerization is concentrated on the fiber surface, the fabric may be sufficiendy stiffer that it takes on a boardy character. As such, the finisher must control the action of agent to give the desired crisp hand but prevent the development of boardiness. Melamines have been recommended for applications when complete shrink resistance is required. However, both finishes were rejected for the white-shirt market because of loss of strength when hypochlorite bleach is used on account of vulnerable NH groups and the ensuing discoloration (37). 

N potassium bromide-bromate so In and 5m of coned HO. Close the flask immediately with the stopper previously moistened with a drop of 10% KI soln, mix the contents by swirling and, after allowing to stand for 10+0.5 mins, add 25ml of 10% KI soln. Titrate the liberated iodine with Q.1N Na thiosulfate soln until near discoloration add 5ml of starch soln and continue titration until the blue color is completely discharged. Run concurrently a blank titration using the same reagents as above... 

Identification Add 0.1 mL of iodine TS to a suspension of 1 g of sample in 10 mL of water, and shake the mixture for 30 s. The reagent is discolored (distinction from polyvinylpyrrolidone, which produces a red color). Add 1 mL of starch TS, and shake the mixture. No blue color appears. 

Spray Reagent Dissolve 1.23 g of p-anisidine and 1.66 g of phthalic acid in 100 mL of methanol. Store the solution in darkness, and refrigerate to prevent discoloration. Discard if the solution becomes discolored. 

Two solutions were prepared for each historical silk sample. Nessler s reagent was added to one, and deionized-distilled water was added to the other, so that an independent measurement could be made of the amount of discoloration contributed to the solution by the silk and its degradation products and contaminants, if any. For these measurements, deionized-distilled water was used as the blank, and a separate absorbance measurement was made on the solution of water and Nessler s reagent. 

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