atratus; a, central medulla of areolar structure; 1, 1, pillars of first or innermost growth; 2, 2, pillars of second layer; d, extremity of firstformed spine; e, extremity of second layer; f, g, h, i, extremities of third, fourth, fifth and sixth layers; b c, line of section across base; kl, line of section across middle. Magnified 7 diam. (§ 112, 113).— Fig. 74. Portion of transverse section of stem of Pentacrinites Briareus. Magnified 20 diam. (§ 120).—Fig. 75. Portion of transverse section of stem of Pentacrinites (species unknown). Magnified 25 diam. (§ 120). PLATE XIX.-Fig. 76. Transverse section of stem of Pentacrinus Caput Medusa. Magnified 15 diam. (§ 120).-Fig. 77. Portion of the external part of the same section more enlarged. Magnified 150 diam. (§ 120). PLATE XX.-Fig. 78. Section of the superficial layer of the shell of Crab, parallel to the surface, showing the reticulated appearance, and the papillary elevations of the subjacent layer. Magnified 75 diam. (§ 127). -Fig. 79. Portion of the same section more enlarged, showing the polygonal cells of which the layer is composed. Magnified 400 diam. (§ 124).—Fig. 80. Portion of transverse section of claw of Crab, near its extremity, showing the fibrous appearance which passes in a radiating manner from one surface to the other; and the parallel lines indicative of successive growths. Magnified 50 diam. (§ 125).-Fig. 81. Portion of the same section more enlarged, showing that the fibrous appearance is given by radiating tubuli. Magnified 400 diam. (§ 125).

Report by the Rev. W. WHEWELL, D.D. and Sir JAMES C. Ross upon the recommendation of an Expedition for the purpose of completing our knowledge of the Tides.

THE knowledge which we possess of the tides, looking at the connexion of the phænomena over the whole surface of the ocean, is extremely imperfect at present, and not at all likely to be completed in any material degree in any finite time, by the observations which voyages mainly directed to other objects will supply. The coasts and islands which surround or break the waters of the Pacific are especially the seats of this ignorance. We know the time of the tide near Cape Horn; but cannot trace the progress of the tide-wave along the western coast of South and North America. We know the time of tide on the coasts of New Zealand; but cannot connect this fact with the rise and fall of the water on the coasts of the smaller islands in the centre of the ocean. We know the tide hour on the eastern coast of New Holland; but cannot trace the progress of the tide to the Philippines, or to the coast of China, though some observations of Admiral Lütke made a few years ago supply a valuable addition to our knowledge on this subject. The course of the tide-wave among the islands of the Indian Sea is likewise unknown. Observations made by voyagers mainly guided by other purposes, appear little likely to supply this deficiency in our knowledge; for even when made with sufficient care and for several weeks at detached places, they are rarely connected with each other or with neighbouring places. It does not appear that while we are thus left to depend on chance for our tidal knowledge, we shall ever be able to know from observation whether the tide-wave in the Pacific does or does not move from east to west.

But a ship sent out on purpose to observe the tides would very soon ascer

tain a great body of facts of this kind. The observers would, of course, observe the facts of the tides in connexion with each other; and would arrange their plan of operation so as to extend their lines of connexion from known points to unknown. By such a mode of proceeding the cotidal lines for every part of the Pacific and Indian Oceans might probably be drawn (omitting the minor details in the interior of archipelagos, &c.) in a year, or at most, in two years.

The tide observations made at the request of Dr. Whewell in 1834 for a fortnight by the coast-guard on the coasts of Great Britain and Ireland, prove how great an accession our tidal knowledge may receive from connected observations; and still more those made in June 1835 for a fortnight along the coasts of the whole of Europe and the eastern coast of the United States of North America. By means of these observations the general course of the tides in the seas thus explored has been determined.

If an expedition were sent for the purpose of making tide observations, it would not be at all necessary to have, as in the instances just mentioned, simultaneous observations along the whole line of sea observed. It would suffice to connect a few places by corresponding observations, in some cases for a fortnight, in others for a few days; then, to connect one of these places with others, and thus to proceed through the whole region observed.

It appears by the experience of the surveys which we have referred to, that the observations may be made by sailors such as those employed on the coast-guard, under proper directions. On those occasions the necessary apparatus was speedily constructed by the persons employed. It might however be useful also to employ, in several places, self-registering tide-gauges, such as are already established in several English ports.

We conceive that the project contemplated by the Association in its recommendation is very desirable; and might best be attained by sending out a vessel which should have for the object of its voyage to make tide observations upon such a connected system. For this purpose, the vessel ought to carry, in addition to a crew sufficient to work her, ten or fifteen men, who by themselves (in pairs), or under the direction of petty officers, might be trusted to make tide observations for a week or a fortnight at selected points of coast. The surveying vessel ought to be provided with a launch, to be employed in carrying these observers to their station, visiting them while engaged in their work, or fetching them away when their task at each place is done. From one region to another of the ocean, standard stations ought to be selected, at which tide observations should be continued for a longer time, and the observations made in each region should be compared with those at the standard station. The comparison of the observations with each other, as the survey proceeded, would point out the direction in which it was desirable to extend the survey, and the special points to be attended to. We therefore recommend that application be made to the Admiralty that they would appropriate to this service a suitable vessel.

On Colouring Matters. By Dr. SCHUNCK.

AT the meeting of the British Association at Southampton I gave a short account of my experiments on the colouring matters of madder. I have continued this investigation, and have found the extent of the subject too great to allow me to devote my attention to any other of the colouring matters. I shall therefore, without any further preface, state the new results which I have arrived at in regard to the chemical constituents of this root.

On treating finely-ground madder roots with boiling water, a brown fluid is obtained having a taste between bitter and sweet. In order to extract all the substances capable of solution in water, about sixteen quarts of water are required for every pound of madder. To this fluid any strong acid, such as sulphuric or muriatic acid, is added in slight excess. Nitric acid must not be used for the purpose. Oxalic acid is best adapted for the purpose, as it can afterwards be completely removed by chalk. The acid produces a dark brown precipitate, which is separated by filtration and washed with water until the excess of acid is removed. The percolating fluid is yellow. This brown precipitate consists of six vegetable substances, viz. two colouring matters, two kinds of fat, pectic acid and a substance of an intensely bitter taste, which I am as yet unable to refer to any known class of bodies. The whole quantity of colouring matter contained in the aqueous extract of madder is precipitated by the addition of a strong acid. In proof of this I took a quantity of the aqueous extract, added sulphuric acid, separated the brown precipitate by filtration and removed the excess of acid with cold water, and then boiled it with water, into which a small piece of mordanted cloth was introduced. The cloth assumed the same colours which it would have done with madder. To the fluid to which acid had been added I put chalk until all the acid was saturated, and I then found after filtering that it communicated no colour whatever to mordanted cloth.

Of the two colouring matters, one is Robiquet's Alizarin, and the other I shall call Rubiacin. Both are contained in the brown precipitate produced by acids in the aqueous extract of madder. In order to obtain them, this brown precipitate is first treated with boiling alcohol until nothing more is dissolved. A dark brownish-purple, somewhat gelatinous mass is left behind, consisting principally of pectic acid. The alcoholic fluid, which contains the two colouring matters together with the fats, has a dark brownish-yellow colour. After being distilled and then evaporated to dryness, a residue of a dirty orange colour remains. This residue is placed on a filter and washed with cold water, until the percolating fluid, which is at first yellow, becomes colourless. On evaporation this fluid leaves a transparent yellow substance with a bitter taste, mentioned above. This substance is soluble in pure water, but insoluble in water containing acids, and hence it is precipitated on adding acid to the aqueous extract of madder; but on washing the precipitate with water, after the acid has been removed it begins to dissolve. In order to obtain it, therefore, the brown precipitate must only be washed so long as it still contains free acid. I shall call this substance Rubian. The mass left undissolved by cold water is then treated with boiling water, and the fluid is filtered boiling hot. On cooling it deposits a quantity of red flocks, which consist of alizarin mixed with fat. This process must be repeated until the boiling fluid deposits nothing more on cooling. If any rubian be still left in the mass on treating with boiling water, the filtration of the boiling fluid is very much impeded, and it is therefore advisable to remove this substance completely with cold water previously to treating with

hot water. The whole of the alizarin dissolved in the boiling water is deposited on cooling, but mingled with fat, which probably accompanies it through the filter in a state of suspension produced by the heat of the boiling fluid. This fat disguises its properties very much, and has been the cause, in all previous investigations, of alizarin never having been obtained in a state of purity except through the agency of heat, which has always left it doubtful whether it existed in the plant as such, or was formed by the action of heat from some other substance. I hope to establish satisfactorily its existence as a constituent of the madder root, and also the fact of its being a pure colouring matter, a circumstance which has likewise been doubted. In order to obtain it in a state of purity, the red flocks which are deposited by the boiling watery solution are separated by filtration and dissolved in boiling alcohol. To the boiling solution, which has a brownish-yellow colour, hydrate of alumina is added, and the boiling is continued for some time. The alizarin combines with the alumina, forming a dark-red compound, while the fluid loses its colour. Fresh alumina is added, until no more colouring matter can be thereby separated. A great part of the fat remains dissolved in the alcohol, while a part combines with the alumina. The coloured alumina is separated by filtration and washed with alcohol for some time. It is then treated with a weak boiling solution of caustic potash, which dissolves the excess of alumina and all the fat which may have combined with the alumina, but leaves the compound of alizarin and alumina undissolved, merely changing its colour from red to dark purple. This process is repeated several times, until the alkaline fluid is no longer red, but of a pure purple colour. The residue is treated with muriatic acid, which dissolves the alumina and leaves the alizarin behind in crystalline flocks of an orange colour, which are washed with water to remove the acid and then dissolved in alcohol. The alcoholic solution on evaporation gives shining, prismatic, orange-coloured crystals of alizarin, which may, if necessary, be purified by a second crystallization from alcohol.

The mass left undissolved by boiling water consists of rubiacin and two distinct kinds of fat. I have only been able to discover one method of extracting the rubiacin from this mixture. This method is founded on the solubility of rubiacin in perchloride and pernitrate of iron. It is immaterial which of these two salts be taken. Persulphate of iron would not answer the purpose. If the mixture of rubiacin with the two fats be treated with a somewhat concentrated boiling solution of perchloride or pernitrate of iron, a solution of a deep reddish-brown colour is obtained, while a brown residue remains insoluble in an excess of the iron salt solution, and consisting of one of the two fats in combination with oxide of iron. The fluid is filtered, and on the addition to it of muriatic acid, a yellow flocculent precipitate is obtained, which is separated by filtration and washed until all the iron salt and the excess of acid are removed. This precipitate consists of rubiacin, the second of the two fats, and of a new body which I shall call rubiacic acid. The latter substance does not exist ready-formed in madder, but is produced by the action of the persalt of iron on rubiacin. This action consists in the rubiacin taking up a certain number of atoms of oxygen from the persalt of iron, and the acid which is thus formed combines with peroxide of iron, producing a compound soluble in water with a reddish-brown colour, and decomposable by any strong acid. Part of the rubiacin however escapes this action, and is precipitated together with the rubiacic acid and fat on the addition of muriatic acid. The precipitate is treated with boiling alcohol, which dissolves the rubiacin and the fat, and leaves behind the rubiacic acid in the shape of a yellow powder. This process is repeated until nothing more is

dissolved by the alcohol. The boiling alcohol, after being filtered, deposits on cooling rubiacin in small shining yellow crystals, which must be purified by recrystallization. The fluid has a yellowish-red colour. On evaporation it gives a quantity of an easily fusible dark reddish-brown fat, which by repeated fusion in boiling water and agitation with the fluid while in a melted state, may be separated from the rubiacin which adheres to it. The rubiacic acid which is left by the boiling alcohol is treated with a weak boiling solution of carbonate of potash, in which it dissolves with a dark brown colour. The solution after cooling and standing some time deposits a mass of brickred needle-shaped crystals of rubiacate of potash, which are easily purified by recrystallization. By dissolving this salt in boiling water and adding any strong acid, rubiacic acid in a state of purity is precipitated as a bright lemonyellow powder. The dark solution from which the rubiacate of potash has crystallized contains a quantity of the brown fat dissolved in the potash.

The brown substance left undissolved by the perchloride or pernitrate of iron is, as I stated above, a compound of one of the two fats with oxide of iron. On being treated with muriatic acid the oxide of iron is dissolved, leaving behind the fat, which, after being washed with water, is dissolved in boiling alcohol. From this it is deposited on cooling as a light brown powder.

I mentioned above that the residue which is left on treating the brown precipitate with boiling alcohol, consists principally of pectic acid. It is treated with boiling water until nothing more is dissolved. The solution, which has a light brown colour, and is somewhat mucilaginous, gives a brown, transparent substance, which easily separates in scales from the sides and bottom of the vessel. After treating the residue with water until nothing more is dissolved, there still remains a dark brown substance undissolved, which I suppose to be a compound of some of the preceding substances with oxide of iron, as it leaves a considerable quantity of ash, consisting of peroxide of iron, on being burnt.

To the aqueous extract of madder, in which the brown precipitate had been produced by oxalic acid, I added chalk until all the excess of acid was saturated, and after filtration I evaporated it. It left a dark brown syrup, which may be separated by means of alcohol into two substances. That which is dissolved seems to be grape-sugar, and that which is left behind is a species of extractive matter, which agrees in its properties with xanthin, as described by Kuhlmann. It has a brown colour. During evaporation in contact with the air it deposits a brown substance or apothegma, like all extractive matters. But it is distinguished from all other extractive matters which I know, by being converted into a green insoluble substance when its solution is boiled with dilute sulphuric or muriatic acid. I have not examined it further, but I may mention that it is probably this body which exerts such a deleterious influence during the process of madder-dyeing, rendering the red and purple brown and unsightly.

I shall now proceed to give a more detailed account of the properties of some of the substances, the methods of obtaining which I have just described. Alizarin.—It is necessary to state that the substance which I called alizarin in the paper read by me on this subject at the Southampton meeting of the British Association, I now call rubiacin. I am of opinion that the substance discovered by Robiquet, and called by him alizarin, does not agree in its properties with that which I call rubiacin; but after carefully comparing his account with the results obtained by myself, I have come to the conclusion that the substance to which I have applied the name of alizarin is identical with his.