Coloring matter precipitation

During aging, the tannins become softer as they polymerize or combine with anthocyanins, while coloring matter precipitates and the color changes. The less oxidized ruby ports maintain the fruitiness and robustness of young wines. They have a more or less dark red color. The older, more oxidized tawny ports are golden red or golden. 

Mineral Substances.—This class comprises only a few materials, which are used rather as body or coloring matters. Svhnitrctle of bismuth is the. pearl white for the complexion. A less objectionable preparation would be a mixture of native sulphate of baryta and prepared chalk—precipitated carbonate of lime, These latter two, while being as white as the former, are not, like it, discolored by the sulphur fumes in the atmosphere, nor SO particularly injurious to the. skin. ... 

This may generally be effected by precipitating the coloring- matter of the sirups with subacetate of lead but at a sugar-work the most convenient and complete method is a filter-of animal charcoal. The filtrates arc than examined optically. When sirups... 

Reducing substances, hexavalent chromium and colored matter, interfere with the test. Reducing substances that may reduce Fe3+ to Fe2+ and thus prevent the formation of thiocyanate complex, may be destroyed by adding a few drops of H202. Add FeS04 to convert CC+ to Cr3+ at a pH below 2. Cr3+ and Fe3+ so formed are precipitated out when the pH is raised to 9 with NaOH. 

The alcoholic solution is concentrated to 1.2 L by evaporating in vacuo and shaken with an equal amount of ether. Dark coloring matters and residues of fat are thus dissolved. The aqueous phase is now mixed with acetone until a precipitate occurs and the dissolved in dilute acetic acid. The solution is brought to a weakly alkaline pH by addition of ammonia. It is then centrifuged and the inactivator is precipitated with five times the amount of ethanol. The yield amounts to about 180.000 kallikrein inactivator units in 0.4-0.5 g of substance. 

Identification An aqueous solution containing 2.8 mg of sample per liter exhibits absorbance intensities (A) and wavelength maxima as follows in neutral (pH = 7) and alkaline (pH = 13) solutions, A = 0.32 at 527 nm with a shoulder at 490 nm. In acid solution, a yellow-brown precipitate forms. Assay Not less than 87.0% total coloring matter. 

Pectin and pectic materials that contain relatively small amounts of other materials can be readily converted to insoluble calcium pectate. When these materials have been isolated from a hardwood or similar material, they consist of pectic acid mixed with hemicelluloses, lignin and coloring matter. To remove these impurities, the material is treated with liquid bromine. The pectic acid and hemicelluloses are precipitated by alcohol and washed with this solvent until free of brominated lignin. The pectic acid is then separated from the hemicellulose by conversion to insoluble calcium pectate. 

The powdered solanaceous plant is thoroughly moistened with an aqueous solution of sodium carbonate and extracted with ether or benzene. The alkaloids are extracted from the solvent with dilute acetic acid, the acid solution is shaken with ether as long as it takes up coloring matter. The acid layer is then rendered alkaline with sodium carbonate, the precipitated alkaloids are collected, washed and dried, then dissolved in ether or acetone. 

Lac resin A purplish-red pigment prepared from lac by precipitation of the coloring matter with a metallic compound Also called shellac. 

Test for the Presence of Blood. Gunning has discovered in acetate of zinc a rea ut that precipitates the slightest traces of tee coloring matter of blood from solutions, even where the liquids are so dilate as to be colorless. Blood washed from the hands in a pail of water can readily be detected in this way. The flocculent precipitate thrown down by acetate of zinc must be washed by decantation, and Anally collected on a watch-glass, and allowed to dry, when the microscope will readily reveal ciystals if any blood bo present. (See Ab. 6415.)... 

Histones are characterized by their basic character . they yield a high percentage of arginine and lysine on hydrolysis. They are soluble in water, and are precipitated on the addition of ammonia. The protein constituent of hemoglobin, the red coloring matter of the blood, is classed as a histone it is called globin. 

It is normal to find potassium bitartrate crystals, associated with precipitated condensed coloring matter, in wine with several years aging potential. When phenols condense, they become bulky, precipitate and are no longer able to express their protective colloid effect. 

---