Colour impart

Procedure (copper in crystallised copper sulphate). Weigh out accurately about 3.1 g of copper sulphate crystals, dissolve in water, and make up to 250 mL in a graduated flask. Shake well. Pipette 50 mL of this solution into a small beaker, add an equal volume of ca AM hydrochloric acid. Pass this solution through a silver reductor at the rate of 25 mL min i, and collect the filtrate in a 500 mL conical flask charged with 20 mL 0.5M iron(III) ammonium sulphate solution (prepared by dissolving the appropriate quantity of the analytical grade iron(III) salt in 0.5M sulphuric acid). Wash the reductor column with six 25 mL portions of 2M hydrochloric acid. Add 1 drop of ferroin indicator or 0.5 mL N-phenylanthranilic acid, and titrate with 0.1 M cerium(IV) sulphate solution. The end point is sharp, and the colour imparted by the Cu2+ ions does not interfere with the detection of the equivalence point. 

The facile phase-transfer catalysed N-alkylation of phenylhydrazones provides an effective route to A-alkyl-A-phenylhydrazines, as shown in Scheme 5.5 [27]. Deprotonation of both the hydrazones and the triazenes leads to resonance stabilized anions. It is therefore highly probable that the alkylation occurs on the initially formed anions, instead of the neutral species, as indicated by the red colour imparted to the organic phase in the reactions of the triazenes, which results from the formation of the ion-pair [Q ArN=N-NAr]. 

Early workers had noted the colours imparted to diffusion flames of alcohol by metallic salts, but detailed study of these colours awaited the development of the premixed air-coal gas flame by Bunsen. In 1859, Kirchhoff showed that these colours arose from line spectra due to elements and not compounds. He also showed that their wavelengths corresponded to those of the Fraunhofer lines. Kirchhoff and Fraunhofer had been observing atomic emission and atomic absorption, respectively. 

Extraneous Colouring Matters.—Most of the products in question are coloured a more or less deep yellow by means of organic colouring matters or, sometimes, saffron, the depth of colour depending on whether enhancement of the natural colour of the flour or imitation f the colour imparted by eggs is desired. In Italy the use of picric acid, Victoria yellow, Martius yellow and metanil yellow for this purpose is prohibited. 

A table showing the colours imparted to the flame by salts of different metals is given in Section V.2(3). Carry out flame tests with the chlorides of sodium, potassium, calcium, strontium, and barium and record the colours you observe. Repeat the test with a mixture of sodium and potassium chlorides. The yellow colouration due to the sodium masks that of the potassium. View the flame through two thicknesses of cobalt glass the yellow sodium colour is absorbed and the potassium flame appears crimson. 

In a limited number of substances containing nitrogen, the presence of the latter may be proved by heating the substance with an excess of pulverised soda-lime in a test-tube with a Bunsen flame this causes decomposition with evolution of ammonia, which is detected by its odour or by means of a black colour imparted to a piece of filter-paper moistened with a solution of mercurous nitrate. Nitro-compounds, eg., do not give this reaction. 

The colours imparted to the flame by salts of different metals are shown in Table 2.1. 

Bunsen was investigating the salts in mineral waters, and he decided to use the flame colours for identification purposes. His new laboratory at Heidelberg was equipped with gas, but Bunsen found that the burners available emitted too much light to observe the colours imparted to the flame by the salts. In conjunction with... 

Decolorizer. A material added to glass to counteract the colour imparted by impurities such as iron the decolorizer may be an oxidizing agent, removing the colour by chemical action, or it may counteract the colour already present by introducing the complementary colour. The materials used include the oxides of As, Ce, Co, Mn, Nd and Se. 

One application where red phosphorus is widely used is for electrical switches and moimtings moulded from glass-filled nylon. These are internal parts where the brick-red colour imparted by the phosphorus is unimportant. Other flame retardants are also effective in nylon but different end uses favour different additives depending on their performance characteristics. This is shown in Table 1 where red phosphorus is compared with a t)rpical halogen system and two other halogen-free additives, magnesium hydroxide and melamine cyanurate. Among the... 

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