RED COLOURS. A. HEAT WITH AMMONIUM SULPHIDE.-A greenish or bluish colour, which, by the action of baryta water, is changed into green-ALOES PURPLE. If the liquid becomes purple, ARCHIL is also present, B. BOIL WITH A SOLUTION OF ALUMINIUM SULPHATE. a. The liquid is coloured red, with a beetle-green reflection-MADDER. (Confirm by spectroscope.) b. The liquid becomes red, but there is no reflection. Add an equal volume of sodium sulphite. (1.) It is bleached. Presence of BRAZIL-WOOD, SANTAL, MAGENTA, CORALLINE, SAFRANIN. BOIL WITH ALCOHOL OF 80 PER CENT. a. The liquid colours distinctly. If bluish-red, MAGENTA; if yellowish. red, SANTALIN. b. Liquid colours very little, or not at all-BRAZIL-WOOD, CORALLINE, SAFFLOWER. (1.) Heat with lime water. No colour-SAFFLOWER. Red colourBRAZIL-WOOD, CORALLINE. (2.) Heat with dilute sulphuric acid. Orange colour-BRAZIL-WOOD, Yellow turning to grey on addition of copper chloride-CORALLINE. (Confirm by spectroscope.) (2.) It is not bleached. COCHINEAL LAC-DYE, LAC-DYE, KERMES, ARCHIL. (a.) Boil with alcohol; liquid becomes red-ARCHIL. If it only faintly colours, or at least if the colour is not decided, it may be COCHINEAL, LAC-DYE, KERMES. (b.) Heat with baryta water; no change-LAC-DYE; the liquid becomes red-COCHINEAL, KERMES. (c.) Heat with lime water: a red colour-KERMES; a violet colourCOCHINEAL. YELLOWS. Heat with a dilute solution of neutral ferric chloride. N.B. This test must be applied when the colouring-matter is separated in a fairly pure state. A. Colour but little altered-ANNATTO, TURMERIC, ANILINE YELLOW, PICRIC ACID, NAPHTHALINE YELLOW. Test with a drop of concentrated sulphuric acid: a blue or green colour is produced-ANNATTO. If the spot becomes at once, or after a little time, more or less brown or red, then add alcohol, with a few drops of hydrochloric acid and some boric acid, (a.) Liquid becomes of an intense pink colour, and on diluting with water, there is a reddish-yellow colour-TURMERIC. (b.) Pale pink colour, on dilution with, water, crimson YELLOW. ANILINE (c.) There is no change of colour on the addition of hydrochloric acid, &c. Heat with ammoniacal copper solution, bluish-green; confirm the presence of picric acid by the cyanide of potassium test, a blood-red colour-PICRIC ACID; the colour becomes an olive greenNAPHTHALINE YELLOW. B. Various shades of colour from green to almost black-MADDER YELLOW, FUSTIC, FUSTET, QUERCITRON, FLAVIN, BERRIES, WELD. Boil with aluminium sulphate, with the addition of an equal volume of water; liquid becomes yellow, with a red reflection-MADDER YELLOW, with tin. Yellow, with a bluish-green reflection-FUSTIC. Liquid yellow without reflection. Heat with baryta water, a red colour-FUSTET. The colour is only darkened. Boil with glacial acetic acid. On cooling, if the liquid is yellow, or greenish-yellow-ENGLISH FLAVIN. If the solution is not at all, or only faintly, coloured, boil with basic lead acetate. This, with regard to fabrics, if a tissue is dyed with WELD, the tissue will not change colour; if with QUERCITRON or BERRIES, the tissue will change to orange-brown; but articles of food will be scarcely coloured with these substances. GREEN COLOURS. If the green colouring-matter is not soluble in water, it is probably chlorophyll, unless indeed it is a mineral colouring substance. Chlorophyll best recognised by the spectroscopic characters of its alcoholic solution (see page 89). If not chlorophyll nor a mineral substance, then A. Boil with a moderately concentrated solution of potassic cyanide. (a.) Colour changes into brown or yellow-ANILINE GREEN, GREEN, containing INDIGO-SULPHURIC ACID (carmine green). (b.) Does not change, or changes into a brownish- or yellowish-green→ GREEN, containing INDIGO with or without CARMINE GREEN B. In any of the foregoing cases add an equal volume of water, and then a solution of aluminium sulphate until an abundant precipitate is formed; filter and wash. (Excess of the precipitate must be avoided.) (a.) Filtrate yellow or reddish—ANILINE GREEN. (b.) Filtrate blue-(1) precipitate colourless-CARMINE GREEN with PICRIC ACID; (2) precipitate yellow-CARMINE GREEN with a vegetable yellow. Dissolve the yellow precipitate in water, add sulphuric acid, and filter: a green fluorescence-FUSTIC; no fluorescence WELD, TURMERIC. Test for turmeric in the original substance by boiling with alcohol, and adding boric and hydrofluoric acids. (a.) Filtrate colourless, precipitate yellow-INDIGO. (b.) Filtrate blue; if the precipitate is colourless, PICRIC ACID may be present, and should be tested for; if coloured, there is probably a vegetable colour present. |