. Plants and their uses; an introduction to botany . ll transformed and dissolved, a pieceof white woolen or cotton soaked in the solution and thenexposed to the air soon takes on a permanent blue color. A considerable number of plants have been found to con-tain indican, and several different species are cultivated inIndia and other warm countries for the manufacture ofindigo. Of these plants the most important one is the dyersindigo shrub (Fig. 275). Logwood is obtained from a small Central American tree(Fig. 276). It is exported in the form of logs from which thesap-wood has been removed. T
. Plants and their uses; an introduction to botany . ll transformed and dissolved, a pieceof white woolen or cotton soaked in the solution and thenexposed to the air soon takes on a permanent blue color. A considerable number of plants have been found to con-tain indican, and several different species are cultivated inIndia and other warm countries for the manufacture ofindigo. Of these plants the most important one is the dyersindigo shrub (Fig. 275). Logwood is obtained from a small Central American tree(Fig. 276). It is exported in the form of logs from which thesap-wood has been removed. The coloring matter whichit yields, is, like indigo, not present in the living plantbut is derived from a colorless glucoside called hcematoxylin(CleHuOe) which in turn readily oxidizes to form the deepviolet-purple compound kno\NTi as hmnatein (CmHioOe). Itis interesting to observe that this transformation involvesthe loss of two atoms of hydrogen just as does the changeof the white indigo into the blue. Unlike indigo, however, COLORING MATTERS 293. Fig. 275.—Dyers Indigo Shrul) (Indigofera tinrtorin. Pulse Family, Le-guminosa). Flowering branch; a, flower, enlarged; h, standard (upper-most petal), back view; c, wing (side petal), inner view; d, e, keel-petal,inner and outer views;/, flower with corolla removed; g. pistil, h, fruit,natural size; i, seed; k, same, cut vertically. (Berg and Schmidt.) —Shrub growing 2 m. tall; leaves downy beneath; flowers reddish yellow,fruit dry. Native home, Southern Asia. 294 1X1 )ISTHIAL PLANTS logwood of itself does not make a permanent dj-e. It requiresthe use of a mordant, that is to say, some substance such asa salt of iron which fixes the dye upon the fabric. Thus usedit makes one of the best blacks for wool or cotton. In com-bination with iron, etc., it is used also widely in the manu-facture of writing inks. Lamphlack is the finely divided carbon deposited fromthe smoke of rosin or oil burned with slight access of air in
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1913
