Fuchsin test

Fuchsin test dilute solutions of triphenylmethane dyestuffs, such as fuchsin (for formula, see Section 4.15, reaction 9) and malachite green, are immediately decolourized by neutral sulphites. Sulphur dioxide also decolourizes fuchsin solution, but the reaction is not quite complete nevertheless it is a very useful test for sulphur and acid sulphites carbon dioxide does not interfere, but nitrogen dioxide does. If the test solution is acidic, it should preferably be just neutralized with sodium hydrogen carbonate. Thiosulphates do not interfere but sulphides, polysulphides, and free alkali do. Zinc, lead, and cadmium salts reduce the sensitivity of the test hence the interference of sulphides cannot be obviated by the addition of these salts. 

The fuchsin test for aldehydes was introduced by H. Schiff, the diazo-benzenesulphonic acid test by E. Fischer and F. Penzoldt. Rosinduline was discovered by O. Fischer and E. Hepp. ... 

Experiment.—Add three drops of glycol to a solution of 1 g. of lead tetra-acetate 2 in 40 c.c. of glacial acetic acid. After half an hour destroy excess of the oxidising agent with a little sulphurous acid, precipitate all the lead with sulphuric acid, filter off the lead sulphate and test the filtrate for formaldehyde with fuchsine-sulphurous acid (see p. 214). The red solution becomes blue on adding concentrated hydrochloric acid (cf. p. 214). 

Experiment 9.—Pure paraldehyde is tested by the previously described aldehyde reactions with ammoniacal silver nitrate, fuchsine-sulphurous acid, and bisulphite solutions. All are negative. 

This scheme of frequency tripling was successfully tested with fuchsin in hexafluorisopropanol (a solvent selected for its low index of refraction and relatively flat dispersion curve) to frequency-triple the output of a neodymium laser 67,68) With an input power of 10 MW/cm2 a third-harmonic output of 0.2 mW/cm2 was measured. This low value was mainly due to the relatively high absorption of fuchsin at 355 nm. An improvement of the efficiency by a factor of 80 was found with hexamethylindocarbocyanine iodide in hexafluorisopropanol because of the much lower absorption of this dye at 355 nm. Since the absorption minimum of this dye is at 383 nm, one could expect an additional efficiency increase by a factor of 70 for a fundamental laser wavelength of 1.15 / 69>. Other cyanine dyes have been used for frequency tripling a fundamental wavelength of 1.89 /mi 70>. 

The test for ethylene glycol was performed by oxidation of the sample with periodic acid and detection of the resulting formaldehyde with fuchsin-sulfurous acid reagent (9). 

Pour 2 ml of a fuchsin (magenta) solution into a test tube and pass a stream of sulphur dioxide through it. What happens Boil the solution. Comment on your observations. How can the occurring phenomena be explained ... 

A similar test involves immersing the moulding in an acid fuchsin stain solution, followed by rinsing under tap water, when the degree of uniformity in treatment can be established by a visual examination of the intensity of the stain and by comparison with a standard that has been treated to a known level. 

Procedure Transfer 10.0 mL each of the Standard Preparation and the Test Preparation to separate 25-mL volumetric flasks. Add 5.0 mL of Potassium Permanganate and Phosphoric Acid Solution to each, and mix. After 15 min, add 2.0 mL of Oxalic Acid and Sulfuric Acid Solution to each, stir with a glass rod until the solutions are colorless, add 5.0 mL of fuchsin-sulfurous acid TS (see Solutions and Indicators), dilute with water to volume, and mix. After 2 h, using a suitable spectrophotometer, concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 575 nm, using water as the blank. The absorbance of the solution from the Test Preparation is not greater than that from the Standard Preparation. PH Determine as directed under pH Determination, Appendix IIB. 

Place 1 drop of the fuchsin reagent on a spot plate and add 1 drop of the neutral test solution. The reagent is decolourized. 

Fuchsin (or Magenta) test The dyestuff fuchsin(I) forms a colourless... 

Examine the effect of heat Heat a small quantity in a small crucible or upon platinum foil. Sulphur will melt to a yellow liquid, and bum with a blue flame with the production of sulphur dioxide (test with potassium dichromate paper or with fuchsin solution). 

Cyanide. This should have been detected and confirmed in the preliminary test with dilute sulphuric acid (Prussian blue test or as Section IV.8, reaction 1). Sulphite. This anion will have been detected in the preliminary test with dilute sulphuric acid (potassium dichromate paper or fuchsin solution test). Hexacyanoferrate(II) (and Thiocyanate). Acidify 1 ml of the soda extract with dilute hydrochloric acid and add a few drops of iron(III) chloride solution. A deep-blue precipitate indicates hexacyanoferrate(II) present. Now add 0-5-1 ml iron(III) chloride solution, 0-2 g sodium chloride and half a Whatman filtration accelerator, shake the mixture vigorously and filter. A deep-red filtrate indicates thiocyanate present. 

Sulphide, cyanide, and sulphite. Acidify 10 ml of the soda extract with dilute acetic acid and boil gently for 3-4 minutes make certain that the solution remains acid (e.g. to litmus) throughout. If sulphite is present, it is advisable to heat the solution for 10-15 minutes (maintaining the volume, if necessary) whilst a stream of air is drawn through it (cf. Fig. IV.2) test for complete removal of sulphur dioxide with fuchsin solution. 

Sulphite, (i) Dilute H2S04 on solid, and action of S02 upon potassium dichromate paper (IV.4, 1). (ii) BaCl2-Br2 water test (IV.4, 2). (iii) Fuchsin solution test (IV.4, 9). 

Thiosulphate, (i) Action of dilute H2S04 upon solid, and liberation of S02 (dichromate paper test or fuchsin solution test) and sulphur (IV.5, 1). (ii) Potassium cyanide test (IV.5, 6). (iii) Nickel ethylenediamine test (IV.5, 9). 

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