tion; to thus overrun it, this population must have been (relatively at least) numerous: add to the two conditions of heathendom and multitude, which may be considered as proved, the third condition of isolation which may be considered as matter for dispute; and then the fourth of this heathendom and isolation lasting from the time of Hengist to that of Augustine; and the present fact of our language being what it is is explained. For proving anything as to the period of which I have been speaking, a period which is rendered Pre-historic, not so much by conditions of time as by conditions of space, the absence of contemporary historians having been entailed by geographical and political isolation, arguments of two kinds, literary arguments and natural history arguments, must be employed. Neither the one kind nor the other is sufficient by itself. The empires of the natural sciences and of literature touch at many isolated points, and here and there they lie alongside of each other along lengthy boundary lines. But empires need not be hostile though they be conterminous; and that the empires of which we have just spoken may be united happily and in a most efficient alliance for work in common, may be seen from the title page of that most excellent German periodical, the Archiv für Anthropologie,' where we have the name of the Physiologist Ecker coupled in editorship with that of the Antiquarian Lindenschmit. The necessity for a combination of the two lines of evidence and argument is as obvious when we have to controvert, as when we have to establish a conclusion. If you have to attack or resist a force comprising both cavalry and infantry, you must have both cavalry and infantry of your own; otherwise some day or other, either in a country intersected with woods, or in some open plain furrowed into deep undulations, one of the two arms in which you are deficient will take you in one or both flanks, and you will be surprised, broken, and routed. [G. R.] WEEKLY EVENING MEETING, Friday, April 1, 1870. SIR HENRY HOLLAND, Bart. M.D. D.C.L. F.R.S. President, PROFESSOR H. E. RoscoE, F.R.S. OWENS COLLEGE, MANCHESTER, On the Artificial Production of Alizarine, the Colouring Principle of Madder. THE speaker stated that he had to bring before the notice of his audience a discovery in organic chemistry which, whether we regard its scientific interest or its practical and commercial value, is of the highest importance, and marks an era in the history of the application of chemistry to the arts and manufactures even of greater importance than the memorable discovery made by Mr. Perkin in 1856 of the production of aniline-violet, or mauve. Since the above-named year great progress has been made in the theoretical investigation of natural and artificial colouring matters as well as in their preparation on a large scale. The chemistry of colouring matters has now taken a high and important position, and chemists instead, as formerly was their wont, of getting rid of all colouring matters as something foreign to their objects of investigation, have, since Mr. Perkin's discovery, found out that the examination of colouring matters may not only lead to scientific laurels, but may sometimes yield fruit of another and not less acceptable kind. We owe to the brains and hands of two German chemists, Messrs. Graebe and Liebermann, this remarkable discovery, which differs from all the former results which have been brought about by the application of science to the chemistry of colouring matters, inasmuch as this has reference to the artificial production of a natural vegetable colouring substance which has been used as a dye from time immemorial, and is still employed in enormous quantities for the production of the pink, purple, and black colours which are seen everywhere on printed calicoes, viz. Alizarine, the colouring principle of Madder. It is from the liquid tarry products of the destructive distillation of coal, a rich source of interest to chemists, that we now derive this new colouring matter. The following Table contains the results of experiments made on the large scale, indicating the various yields of tar from different qualities of coal distilled in the gasworks of various towns : DESTRUCTIVE DISTILLATION OF COAL. 100 tons of Cannel and Bituminous Coal distilled to yield 10,000 cubic feet of gas of spec. grav. 0.6, yield the following products: From a careful series of experiments made by a large tar distiller, the following numbers are derived, showing the average composition of gas tar : It is from Benzol, C. He, discovered by Faraday in 1825, that the aniline colours are all of them prepared. The colour-producing power of the coal products are, however, yet far from being exhausted. It is by means of another and hitherto comparatively unknown hydro-carbon, Anthracene, C1, H10, that the newest triumphs of the chemist have been won. This is a substance which in the pure state few chemists (even yet) have seen, and upon which only two or three had previously experimented, and yet by one happy discovery-and by an investigation which more than almost any other exhibits the value of the synthetic power of modern research-this unknown body has been made to yield a colouring matter of the greatest possible value. The truth of this will at once be evident when we learn that the total growth of madder is estimated to reach 47,500 tons per annum, worth 451. per ton, and having, therefore, a value of 2,150,000l. Of this nearly one-half is used in the United Kingdom, so that no less a sum than 1,000,000l. is now paid by us for madder grown in foreign countries. This will now, in part at least, go to benefit our own population, as we can now transform our coal into this invaluable colouring matter. In an experiment made on a large scale it was found that 100 tons of tar yielded 0.63 ton of anthracene, or 1 ton of anthracene can be obtained from the distillation of about 2000 tons of coal, not reckoning the quantity of anthracene contained in the pitch. Madder is the root of several species of Rubia, amongst which the Rubia tinctorum is the most valued for its dyeing properties. This grows in Holland, Asia Minor, and in the south of France and of Russia. A species native to England is the Rubia peregrina. This belongs to the order Rubiacea, the native members of which, as the Galiums, are mostly inconspicuous wild plants. Some of the foreign species are on the contrary important plants, such as the Cinchona, Ipecacuanha, and Coffee plants, and these are distinguished for the number and variety of the peculiar principles which they yield, as quinine, cinchonine, caffeine, alizarine. Thanks to the kindness of Dr. Schunck, the speaker was able to show a young madder plant. In spite of the many investigations which have been made of madder, chemists are still in doubt as to the nature of many of its constituents. Some attribute its colouring powers to the presence of at least two substances-alizarine and purpurine-whilst others say that only one of these produces the true madder colours. Alizarine was discovered and obtained from madder, as a crystalline sublimate, by Robiquet and Colin, in 1831, but little importance attached to this discovery until Schunck, in 1848, showed that all the finest madder colours contain only alizarine combined with bases and fatty acids. The second colouring matter, termed Purpurine, was discovered by Persoz. It contributes to the full and fiery red colour in ordinary madder dyeing, but dyes a bad purple, alizarine being essential to the latter. Purpurine disappears during the purifying processes of soaping, &c., being far less stable than alizarine. It is distinguished from alizarine by its solubility in boiling alum liquor. These two colouring principles may likewise be easily distinguished by the spectrum, alizarine producing a set of dark absorptionbands, quite different from those of purpurine, which again vary according to the nature of the solvent. Alizarine can be obtained in yellow needle-shaped crystals by simple sublimation from the dried madder; but this colouring matter is, singularly enough, not contained ready formed in the fresh madder root, but is the product of a peculiar decomposition. For a proof that fresh madder does not contain alizarine we have only to extract the moist root with alcohol, when neither the alcoholic extract nor the insoluble residue will be found to possess tinctorial power. We owe this knowledge to the researches of Schunck and Higgin, who have proved that alizarine is produced by a peculiar kind of fermentation which partly occurs in the root on standing, and partly takes place in the dyebeck, when the powdered madder is treated with water. A crystalline glucoside, termed Rubianic Acid (Schunck), is contained in the root, and it is this which splits up simply into alizarine and glucose. This acid crystallizes in fine yellow needles, and gives a definite and crystalline potash salt, from which it was shown to contain 26 atoms of carbon in the molecule. Hence, as no other product but glucose is formed, it follows that alizarine must contain C2 - C12 = C. This decomposition of rubianic acid into alizarine was shown by boiling with an acid, and adding caustic soda when the blue solution of alkaline alizarine was seen. The formation of alizarine in extracts of madder root is effected by a ferment peculiar to the plant, and called Erythrozym. It is a ferment sui generis, since no other ferment produces the same effect. When mixed with a solution of rubian or rubianic acid, at the ordinary temperature, the latter is rapidly decomposed as with acids. This is what takes place in making fleur de garance. Dyers raise the temperature of their madder-baths gradually up to the boiling-point, because the application of a high temperature destroys the ferment. When the temperature is gradually raised, the ferment acts upon the glucoside, and produces alizarine. That the colouring matter in fresh madder root is not alizarine can be easily shown by rubbing the soft portions of the root on to paper, when a yellow stain will be produced, which, on treatment with an alkali, shows the bright red colour of an alkaline solution of rubian instead of the blue solution of alizarate. According to Schunck, the origin of purpurine, and its relation to alizarine, are still involved in obscurity. The hypothesis which of late years has done more than any other to stimulate experiment and enlarge our views in organic chemistry is undoubtedly Kekulé's theory of the Tetrad nature of Carbon and his explanation of the constitution of the Carbon Compounds. In the socalled Paraffine group of organic substances, the carbon atoms are supposed to be connected together by single links of the four bonds attached to each atom, thus giving rise to saturated compounds by the attachment of other elements or radicals to the free bonds. In the group of aromatic substances with which we are specially concerned the carbon atoms are more closely linked together, or in other words, a less number of atoms of hydrogen are necessary to saturate an aggregation of carbon atoms than is the case in the other group. We can explain this, upon the assumption of the tetrad character of carbon, by supposing that each carbon atom is attached to its neighbour alternately by one and by two bonds. Another singular property of these aromatic bodies is that they all contain at least six atoms of carbon and that the simplest hydrocarbon of which they are made up is Benzol C, H.. So that we may regard all these aromatic compounds as Benzol derivatives, and this hydrocarbon may be considered as the skeleton round which many complicated substances are arranged. So that by the replacement of one atom of hydrogen by N H, we obtain Aniline, by OH Phenol, &c. From the knowledge gained by his investigation on the Quinones, |