PRELIMINARY EXPERIMENTS ON FEATHER PIGMENTS' BY WILDER D. BANCROFT
The experiments described in this paper were made by Mr. J. R. Adams. The pigment in the feathers of the Cock of the Rock was extracted with alcohol and some dyeing tests were made with the yellow solution. In a slightly acid solution wool was dyed yellow; in a neutral solution wool was dyed a paler yellow; and in a slightly alkaline solution no perceivable color was imparted to the wool. Silk was also dyed yellow in a slightly acid solution, while cotton was not dyed a t all. Alumina from aluminum was colored yellow. The pigment t#hereforebehaves like an acid dye. The pigment can also be extracted from these feathers by means of a hot sodium carbonate solution. In the next set of experiments, the skin of a cardinal was obtained from Professor Arthur A. Allen. The feathers were removed and washed with water to remove such dirt as could be removed. Treatment with a sodium oleate solution removed the color completely, leaving a perfectly white feather; but no good way was found to separate the dye from the sodium oleate solution. If acid is added, the color is thrown down as a reddish brown precipitate. The feathers were therefore extracted with alcohol, and a yellow solution was obtained having apparently just the same color as the corresponding extract of the feathers of the Cock of the Rock. The pigment comes out readily a t first and then more slowly and the feathers always retained a certain reddish tinge. This residual color seems to he the characteristic pink, which differentiates the cardinal feathers from those of the Cock of the Rock. The dyeing experiments came out exactly like the preceding ones. Diffusion experiments with the two pigments in acid, basic, and neutral solutions gave the same results, and it was also found that the pigment could be estracted from the cardinal feathers with a hot sodium carbonate solution. The absorption bands were determined roughly for each solution spectroscopically and thc solutions scemed practically identical. Some experiments were also made as to the fading of the colors on exposure to light. Feathers from the Cock of the Rock and from the cardinal were placed in a Fadeometer. The feathers from the Cock of the Rock changed in a few hours to yellow and then to white. The feathers from the cardinal took a much longer time to fade but the change was to a dark yellow and then to white. I n both cases the solutions leave an orange-red residue if allowed to evaporate a t room temperature. It seems probable therefore that the pigment in the feathers of the Cock of the Rock is substantially identical with that in the feathers of the cardinal, though it is not proved that the identity may he only in the extracted pigments. 1 The investigation upon which this article is based was su ported by a grant from the Heckscher Foundation for the Advancement of Research, estaglished by August Heckscher at Cornel1 University.
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The question arises, however, why a red pigment should dye yellow. There w e two possible answers. The red pigment may be decomposed into a yellow pigment, during extraction, or the red and yellow pigmentts may be ident,ical chemically, the difference being purely a question of aggregation. We know that ferric oxide (rouge) and potassium ferricyanide are red in coarse crystals and are yellow when very finely divided. It is not possible at preeent to decide between these two hypotteses; but it is intereeting to note that an orangered precipit,ate was obtained when the soluticns evaporat'ed, which should not be the case if the red pigment had decomposed. When the red feathers of the red-headed woodpecker are extracted with alcohol for ten hours, they change to a light. shade .of gold, and the red feathers of the red-winged blackbird change to yellow under the same conditions, after which t,here is practically no further extraction. In the case of the fruit pigeon, the yellow was extract.ed completely in ten hours; but, the red was not affected a t all. 7 he red of the scarlet tanager is extremely resistant to alcohol and so is the brown of the canvas-back duck. It seems probable that there are a t least two groups of red or yellow colors, t,hose which are extremely resistant to alcohol and those which are not. There is no doubt as to the apparent difference between them; but it is of course poseible that there is some other substance present in the feathers in one set, of cases which acts as a mordant and retards ext,rac,tion. There seems also to be a very distinct relation between the resistance to extraction by alcohol and the resistance to fading in light. The brown of the canvas-back duck and the red of the scarlet tanager are practically fast to light. The yellow Toucan feathers hleach in six hours in the Fadeometer and the red, changes t0.a brown which bleaches on a longer exposure. Both colors come out readily with alcohol, W-ith the fruit pigeon the yellow faded rapidly while the red did not. The feathers of the Blue and Yellow Macaw were exposed in the Fadeometer for 105 hours, at which time the orange had changed to a yellow which was not removed by further exposure. On extraction the orange changed to a lemon-yellow, which could not be extracted. On the other hand the yellow of the golden pheasant can be extracted in about sixteen hours and fades in less than fifteen hours. If one wished to make three classes, one could take the toucan, golden pheasant, and cardinal as.having pigments which fade readily and which are easily extracted with alcohol. The feathers from the fruit pigeon, the blue 'and yellow macaw, and the yellow-headed Amazon parrot fade slowly and the pigment can only be extra,cted slowly. The black of the crow, the brown of the canvas-back duck, and the red of the scarlet tanager do not fade at all and are almost, impossible to extract. It, is well known that the reds of the bronze-headed trogon and of the flamingo are extremely fugitive to light. No experiments have been done with these to determine resistance to extraction by alcohol.
FEATHER PIGMENTS
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Lloyd- Jones,’ is evidently of the opinion that reds and yellows in feathers are identical chemically. “Among self-colored birds the colors red and yellow are perfectly distinct. Even the lightest reds and the darkest yellows an’ easily placed in their proper class, In appearance these colors bear the relation to each other of dilute and intense conditions of the same pigment’ material. That yellow is a dilute condition can be demonstrated by even a hasty examination of the feathers, and the fact is farther borne out to the degree of certainty by a comparative chemical study of the two different kinds of feathers. Microscopically, the ‘yellow’ pigment is seen to be far more sparsely distributed than in .reds. Often under strong light the pigment in the barbules is almost imperceptible. . . . “The crucial difference between yellow and red, however, has not yet been mentioned, It is concerned with the nature and form of the pigment granules. As shown above, the pigment in reds exists as distinct, clear-cut, spherical ~ diameter. No such spheres have ever been found granules, typically 0 . 3 in in yellow feathers, in the course of my work. The pigment exists as irregular formless clumps, or agglomerations. These blotches of pigment appear finely granular in nature; but are so fine that discrete particles are beyond the limits of a IS mm oil immersion objective. This difference between reds and yellows is sharp and is constant. When minute patches of reddish pigment are present on a dun, black, or white feather, it is frequently difficult or impossible by gross examination to classify the color as red or yellow; but miscropic study of such areas serves unfailingly to distinguish the colors by virtue of the morphological difference above cited.” On a later page Lloyd-Jones draws the following conclusions:I. There is a red-brown pigment substance which produces the colors red and yellow in tumbler pigeons. 2 . I n red birds this pigment always exists as spherical granules, which are in ‘typical red’ about 0 . 3 ~in diameter; but in ‘plum color’ they are 2 . 0 ~or more in diameter.
3. I n yellows the pigment is so finely divided that its granule form cannot be determined.
It is possible that these generalizations apply only to the material studied by Lloyd-Jones; but they are certainly interesting and they may turn out to be quite general, though it is rather to be expected that different yellowsand consequently reds-will show up differently under the microscope. The general conclusions of this paper are as follows:I. Some reds and yellows are very resistant to extraction with alcohol while others are not. Those reds and yellows which are not easily extracted by alcohol are pretty fast to light and the converse seems also to be true.
‘J. Exp. Zoology, 18, 464 (1915).
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2. When extracted by alcohol, the red and the yellow pigments give yellow solutions which are apparently identical. It is not known whether the red pigment is converted into a yellow one a t the time of extraction or whether the red pigment differs structurally from the yellow one in being coarser, just as we know is the case with red and yellow mercuric oxide, ferric oside, and potassium ferricyanide.
3 . The extracted pigment behaves like an acid dye because it does not dye cotton direct and dyes wool most strongly in an acid bath and least strongly (or not at all) in an alkaline bath. It is also taken up to Pome extent by alumina
