the dark or black portions remaining unchanged. Touracous in captivity have been known to reduce their splendid crim son decorations to a shabby pink by too frequent ablutions with rain-water! The red pigment separates from its solution in ammonia or other alkali when a strong acid is added, in flocks, which may be dried into a rich crimson solid. This, when analysed, contains, along with carbon, hydrogen, nitrogen, and oxygen, about 8 per cent of copper, this copper being so bound up with the other elements present as to be incapable of removal by any treatment of the pigment short of its entire destruction.'1 The existence of an animal pigment so rich in copper as turacin, offers many interesting problems for study. Traces of this metal seem generally diffused in most vegetables and many animals; but here are more than traces-weighable and visible quantities. It is true that these plantain-eaters have been seen to pick up in their native countries grains of malachite, the green mineral carbonate of copper; but we must rather look to the vegetable food they consume as the true source of this metal. And when the copper has been ingested, how does it find its way, in the complex pigment of which it is an essential part, precisely to those feathers, and to those barbs of feathers, and to those parts of such barbs, which are red, and not to the black portions? For if one of these feathers is burnt in a Bunsen gas-burner, not till the red part of the feather is reached will the green flash of the copper tinge the flame. However, in the crest of the violet plantain-eater (Musaphaga violacea), and perhaps in traces in the blood of all these birds, turacin, and therefore copper, does occur. Still the whole mystery of this strange pigment is far from being understood. 3. A word or two about a third animal pigment must suffice. In the black and dark feathers of some birds, in black human hair, and possibly in the skin of some mammals, a black pigment is found. It is a remarkably stable compound, resisting the action of such a powerful chemical agent as tolerably strong sulphuric acid. Sorby obtained 1 grain of it from 100 grains of the feathers of the rook (Corvus pica), and found it to contain the following average 1 See, for further details, Church on Turacin, in the Philosophical Transactions of the Royal Society, 1869, pp. 627-636. percentages of these four elements: carbon, 55.4; hydrogen, 4.25; nitrogen, 8.5; oxygen, 31.85. The chemical and physiological relationships of this pigmentum nigrum are at present unknown. It differs widely from albumen, though it may be a product of its decomposition. 4°. Turning to the colouring matters of plants, leaf-green, or chlorophyll, in virtue both of its importance and abundance, claims the first place. Strange to say, however, in spite of the thousands of tons of this substance which are annually produced by grasses, herbs, and forest-trees, chemists have not yet ascertained its component elements, much less their relative proportions. We do not know whether it contains iron or nitrogen, although we are sure that it is never produced in the absence of compounds capable of supplying these elements. And further, it is possible that leaf-green may consist of more than one substance, or that the leaf-green of all plants may not be identical in every respect. Still some progress has been made in the study of this colouring matter, and a good many facts about it have been ascertained. It occurs, for instance, in all land plants having an independent existence-that is, not living upon other growing organisms, or on decaying organic matter. Chlorophyll, moreover, is found in those cells of plants where the absorption and decomposition of carbonic acid gas goes on, with which characteristic process of vegetable life it is closely concerned. Thus starch-granules are formed in such cells in the midst of a complex material to which the name of protoplasm is given, this protoplasm or formative substance being dyed, as it were, with chlorophyll. It is, then, extremely probable that chlorophyll, when under the influence of the sun's radiant energy, stands, in relation to the carbonic acid gas which plants decompose, very much in the same position of importance as hæmaglobin does to the gases of the blood. One of the most characteristic properties of chlorophyll is the action of its solutions on light. The solar rays in part pass through the liquid, which appears green by such transmitted light. But in part they are reflected from its surface, and from some depth beneath, and become so changed thereby as to appear red. Thus a fresh solution of chlorophyll in ether is perfectly clear and green when you look through it, but on being looked at, it seems to be full of minute particles of vermilion-it is an opaque red. 5°. It has long been known that many flowers, fruits, and even leaves, give to spirit of wine a colouring matter which is scarlet with acids, violet or purple in a neutral liquid, and blue or green in the presence of an alkaline substance like soda-dahlia-flowers, grape-skins, and red-cabbage leaves are examples. One colouring matter is probably common to all these plants and to many others. It has been called by many different names, but quite lately has been termed colein, from Coleus, a genus of plants, in many species of which it occurs abundantly, both in stem and leaf. There is scarcely a doubt that it is closely allied to chlorophyll, but, unlike that pigment, it has no important office to fulfil in the plant. It is distributed in the most curious manner in the parts of the plants where it is found. In a leaf of Coleus, say C. verschaffelti, it is irregularly distributed in the cells of Coleus verschaffeltii. a, Leaf, half natural size, showing distribution of colouring matter. the epidermis (a, fig. 88), some of these containing much, some a trace, and others none. But its mode of occurrence in the hairs of the stem and leaf is still more curious; a hair 1 See Church on Colein, Journal Chem. Society, 1877, i. 253-262. made up of, say, six cells, may have the end-cells richly tinted, and all the others free from colein. (See b in fig. 88.) Colein is a red resinous-looking substance, which will not dissolve in ether, and but slightly in water, but is very soluble in spirit of wine. A weak alcoholic solution becomes nearly colourless after a few moments, but when it is poured on a porcelain plate it regains its colour as it dries up. With a drop of ammonia solution the colein becomes purple, violet, indigo, green, and then yellow; with a drop of acid it takes a scarlet hue. Colein has the percentage composition, carbon, 57.7; hydrogen, 4.7; oxygen, 37.6. It is probably thus identical with the colouring matter of red wine, most red, blue, and purple flowers and fruits, and with the red pigment of the copper beech. Its solution forms a very sensitive test-paper for acids and alkalies. 6°. A third vegetable pigment, the chief colouring substance to which madder-root (Rubia tinctorum) owes its value as a dye, affords a most striking example of the methods and results of modern chemical research. After many long and tedious investigations as to the composition and relationships of this madder pigment, called alizarin, Graebe and Liebermann decided that its chemical composition was represented by the expression, C14 Hg 04. These chemists further ascertained that it yielded a hydrocarbon (that is, a compound of carbon and hydrogen), having the formula C14 H109 when distilled with zinc-dust and zinc-hydrate. Now this hydrocarbon, called anthracene, was already a well-known substance, which could be made from several chemical compounds, and occurred in considerable quantities in the less volatile parts of coal-tar. If alizarin, the red pigment derived from madder, gives anthracene, may not anthracene be made to give alizarin? The German chemists above named accomplished this transformation also. By a process which is essentially one of oxidation, two of hydrogen are taken away from anthracene, and four of oxygen added. This process, as improved by Perkin, consists in oxidising the anthracene by bichromate of potassium, heating the anthraquinone (C14 Hg O2) formed with oil of vitriol, and then treating the last product with caustic potash. The materials being cheap, alizarin thus made has displaced the preparations from madder-root to a great extent, so that the growth and imports of that valuable plant have greatly fallen off since this grand and almost unique discovery of how to prepare artificially a vegetable colouring matter. It is believed that the madder-root (much is grown at Avignon) used in this country in the three years following the discovery, chiefly for dyeing "Turkey red," is represented by the following values: 1874, 1876, £800,000 411,000 239,000 Strange that the heating of a few scarlet crystals with some powdered zinc in a test-tube should have produced so considerable an effect on commerce, destroying an old industry and creating many new ones. But the chemistry of the last thirty years has furnished many equal marvels, while the chemistry of the future promises to be still more fruitful. In this same matter of pigments scores of new and splendid dyes have been produced. Indigo, too, that old favourite, the prince of pigments, has at length revealed the secret of its structure to the questionings of the chemist, so that the elements of this colouring matter can now be put together without the assistance of the organic processes going on in the indigo-plant. But as yet the artificial building up of indigo is too costly and elaborate a process to be commercially available. 7°. With the coal-tar colours we are almost too familiar nowadays. Some of these colours in chief request are distressingly violent, and being often used unmixed and in masses fatigue the eye. The passing rainbow, set in a vast expanse of shaded grey, is pleasant and refreshing; but we should soon be wearied of a sky for ever filled with great arches of pure prismatic hues. But whatever the artistic and decorative failings of the coal-tar pigments as commonly employed may be, the chemistry of these brilliant and complex compounds is full of interest. It was in the spring of 1856 that the first of the coal-tar dyes saw the light. Mr W. H. Perkin, then a young student of the College of Chemistry, during some experiments preparatory for an entirely different research, had occasion to attempt the oxidation of a liquid derived from coal-tar, and called aniline. Aniline (itself formerly made only from |