. Biological stains, a handbook on the nature and uses of the dyes employed in the biological laboratory. Stains and staining (Microscopy). 3. THE OXYQUINONE GROUP The oxyquinone dyes include derivatives of anthracene,. thru its oxidation product anthraquinone O O These dyes are the first to be considered here in which the quinoid structure occurs. The quinoid ring, which is the most important chromophore in nearly all the dyes to be discussed in the three fol- lowing chapters, forms very strong chromogens, which require only the addition of auxochrome groups to be converted into strong dyes,
. Biological stains, a handbook on the nature and uses of the dyes employed in the biological laboratory. Stains and staining (Microscopy). 3. THE OXYQUINONE GROUP The oxyquinone dyes include derivatives of anthracene,. thru its oxidation product anthraquinone O O These dyes are the first to be considered here in which the quinoid structure occurs. The quinoid ring, which is the most important chromophore in nearly all the dyes to be discussed in the three fol- lowing chapters, forms very strong chromogens, which require only the addition of auxochrome groups to be converted into strong dyes, either basic or acid. The chromogen anthraquinone is con- verted into a dye by the addition of hydroxyl groups, its best known derivatives among the dyes being: 1:2 dihydroxy-anthra- quinone (alizarin) and 1:2:4 trihydroxy-anthraquinone (purpurin). Both of these compounds occur in nature in the root of madder, being the colored principles of madder extract. They have the prop- erty of combining with metalic oxides to form so-called "lakes", insoluble compounds of different color from the dye entering into them. This makes them valuable ones to use after mordanting with aluminium, iron or chromium compounds. ALIZARIN O OH II / OH C. I. NO. 1027 II, O {An acid dye; absorption maxima about [], , [] in alkaline solution.) Alizarin stains tissues a feeble yellowish red if used on them directly. In the presence of aluminium compounds intense red colors are formed; bluish violet in the presence of iron; and brown- ish violet in the presence of chromium. It has been used as a stain for nervous tissue. The chief present use of alizarin, however, is as an indicator. 42. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Conn, H. J. (Harold Joel), 1886-1975; Ambler, Joseph Alfred, 1889-; Kornhause
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