chloride of tin a dirty yellow precipitate; with perchloride of tin a light yellow precipitate; with chloride of gold a yellow precipitate, not changed by boiling the fluid.

15

I have analysed rubiacin, rubiacic acid, and rubiacate of potash, and have obtained results which agree very well with one another. These analyses give for rubiacin the formula C, H, O10, for rubiacic acid C, H, O17, and for rubiacate of potash C, H, O15 + KO. It therefore appears that rubiacic acid contains seven atoms of oxygen more than rubiacin, and the facility with which they may be converted one into the other is easily conceivable. In rubiacate of potash two atoms of water existing in rubiacic acid are replaced by one atom of potash, which is not usually the case with potash salts. I do not, however, consider these formulæ as completely established, since I was obliged, from want of material, to operate on such extremely small quantities.

Rubian. This substance is obtained, as I mentioned above, by treating the brown precipitate produced by an acid in an extract of madder with cold water, after having removed the excess of acid. It has the following properties:

In thin layers it is perfectly transparent and of a yellow colour. When dry it is brittle. It is soluble in water; the solution has an extremely bitter taste. A concentrated boiling solution forms a jelly on cooling. It is precipitated from its aqueous solution by all acids, in yellow flocks. It is decomposed by nitric acid. In the watery solution lime and baryta water produce red flocculent precipitates, perchloride of iron a dark reddish-brown colour, but no precipitate, sugar of lead a brown flocculent precipitate, nitrate of silver a flocculent precipitate, corrosive sublimate no precipitate, tincture of galls and solution of glue no precipitates. The solution imparts a slight tinge to mordanted cloth, but so slight that this substance cannot be considered as a colouring matter. The solution deposits nothing during evaporation at all resembling apothem, and it therefore is not extractive matter. It dissolves in alcohol with a yellow colour, and in alkalies with a red colour. It dissolves in concentrated sulphuric acid with a red colour; the solution on being heated becomes black, and gives off sulphurous acid. When heated on platinum foil it melts, swells up immensely, and burns, leaving some ash. When heated in a tube it melts and gives yellow fumes, which condense and form a crystalline sublimate very much resembling rubiacin, so that I am induced to think that there is some relation subsisting between these two substances.

Pectic Acid.-There can hardly be a doubt, I think, that that part of the brown precipitate which is insoluble in alcohol, but soluble in water, is pectic acid, as will be seen from its behaviour towards reagents, which is as follows: -It is soluble in water; the solution has a light yellow colour, and reddens litmus paper slightly. In the watery solution acids produce white flocculent precipitates, alcohol a gelatinous white precipitate, lime and baryta water thick gelatinous pink precipitates, common salt a flocculent precipitate, nitrate of potash a flocculent precipitate, sugar of lead a gelatinous reddish precipitate, sulphate of copper a gelatinous greenish precipitate, corrosive sublimate no precipitate. On evaporating the watery solution, the substance separates on the surface of the fluid in the shape of a pellicle, and is left at last as a brownish extract, which may easily be detached from the sides of the vessel. In solutions of caustic and carbonated alkalies it first swells up, and on heating the fluid it dissolves with a light red colour, forming slimy fluids, from which it is precipitated by acids in flocks. Solutions of salts, even of alkaline salts, produce precipitates in the alkaline solutions. It is

decomposed by boiling concentrated nitric acid. When heated on platinum foil it burns without melting, leaving a considerable ash. It seems that the pectic acid from madder retains in combination with it a portion of colouring matter, from which it cannot be separated. Hence the red colour with which it dissolves in alkalies.

Concerning the two fats which I mentioned above as constituents of the brown precipitate, I have little to say. They also retain in combination a quantity of colouring matter, from which I have found it impossible to separate them. They are both soluble in alcohol, but one more so than the other. One of them dissolves with rubiacin in perchloride of iron, the other not. The former is more easily fusible than the latter, but both melt below the temperature of boiling water.

I shall conclude this paper with some practical deductions which I have made from the experiments detailed in the preceding.

Few subjects connected with the arts have raised so much discussion as the nature of the process of madder-dyeing. The investigation of Robiquet on this subject, instead of clearing it up, seemed only to add to its complexity. He considered his alizarin as the substance mainly concerned in the production of madder colours. This has been denied by others, though I think on insufficient grounds. A remarkable discovery in regard to madderdyeing, was the fact that lime is very essential in this process. It was found that madder, if not grown on calcareous soil, is incapable of producing fast colours, but that if in this case chalk be added to the madder during dyeing, or if calcareous water be employed, the desired effect is produced. This again has given rise to endless discussions. It was found by Persoz that the minutest quantity of lime added to alizarin impaired its colouring power during dyeing, and the effect of lime in madder-dyeing appeared to him an inexplicable mystery. I will not enter further into the disputes on this subject, but shall state at once my own views. It seems to me that former investigators have erred in supposing that madder contained only one colouring matter, whereas I think I have proved that there are two, perfectly distinct and definite, alizarin and rubiacin, which perform distinct functions during the process of dyeing. I have found, as I stated above, that of the two colouring matters, alizarin and rubiacin, the former is the only one that is capable of dyeing when in a free state, and further, that the brown precipitate produced by acids in a watery extract of madder contains the whole of these two colouring matters in a free state. If then a piece of mordanted cloth be dyed with this brown precipitate, after being freed from all excess of acid, the whole effect is produced by the alizarin contained in the brown precipitate. If, however, a small quantity of lime, chalk, soda, or any alkaline base, either caustic or carbonated, be added to the brown precipitate before dyeing, then its power of dyeing is very much increased. In order to prove this, I took six pieces of mordanted cloth, all of the same size. Nos. 1, 2 and 3, were mordanted in the usual way with acetate of alumina, and Nos. 4, 5 and 6 with acetate of iron. Nos. 1 and 4 were dyed with a certain quantity of the brown precipitate; Nos. 2 and 5 with the same quantity of the brown precipitate, to which, however, there had previously been added a very small quantity of lime water; Nos. 3 and 6, lastly, with the same quantity of brown precipitate, and a large excess of lime water. The dyeing was performed each time in the same vessel with the same quantity of water, and for the same length of time. Now I found at the conclusion that No. 2 exhibited a far darker, fuller, and more brilliant shade of red than No. 1, and No. 5 a much more intense purple colour than No. 4, whereas Nos. 3 and 6 showed hardly any colour at all. Now I can offer only one explanation

of these differences. When a small quantity of lime is added to the brown precipitate, it combines exclusively with the rubiacin, or is transferred during the process of dyeing exclusively to the rubiacin. The first effect of the dyeing is the combination of the alizarin with the alumina and peroxide of iron of the mordants. These compounds then attract and combine with the lime compound of rubiacin contained in the fluid, by which means a greater intensity of colour is produced. I repeated this experiment with the pure colouring matters. I took two pieces of mordanted cloth of the same size, and dyed the one with pure alizarin, and the other with the same quantity of alizarin to which rubiacin combined with lime was added, and I found that the latter was much darker than the former. I therefore conclude that madder colours are always double compounds of alizarin, rubiacin, alumina, and an alkaline base, or of alizarin, rubiacin, peroxide of iron, and an alkaline base.

It follows from this that the maximum of tinctorial power in madder is produced when the alizarin is in a free state, and the rubiacin is in combination with lime or some alkaline base. If an excess of lime be added then the alizarin also combines with it, and is thus rendered incapable of attaching itself to the alumina and peroxide of iron of the mordants. A slight excess of lime exists in the root when grown on a calcareous soil; for if a quantity of madder which has dyed as much cloth as it is capable of doing and is seemingly quite exhausted of colouring matter, be treated with sulphuric acid, and the acid be carefully removed by washing, it is found that after being so treated it is capable of again dyeing almost as much mordanted cloth as it did before, a fact long known in practice. I may state in addition, that the colours produced by the brown precipitate to which a small quantity of lime has been added, resist the action of soap and acids, &c., to which all madder colours must be subjected in order to heighten them, much better than if no lime had been added. I therefore conclude, that though the possibility in general of dyeing with madder is due to alizarin, the solidity and brilliance of madder colours must be ascribed to rubiacin.

Seventh Report of a Committee, consisting of H. E. STRICKLAND, Esq., Prof. DAUBENY, Prof. HENSLOW, and Prof. LINDLEY, appointed to continue their Experiments on the Vitality of Seeds. THERE has been this year a second sowing of the seeds collected in 1837 and in 1844, and in addition to these, ten kinds of new seeds gathered in 1846 have been proved. These were the entire number available for the purpose, selected from a great quantity presented by Miss Molesworth, of Cobham, Surrey; the remainder consisted of kinds previously tested, or were not in sufficient quantities for general distribution or preservation, and according to her instructions were sown in the Oxford garden*.

* With these seeds Miss Molesworth sent the results obtained by herself, after sowing a great number of seeds of various dates (from 1827 to 1845 inclusive), at Cobham Lodge in 1846; by which it appears that none of greater age than those gathered in 1834 vegetated, and of this date one kind only, viz. the Stone Pine, three seeds of which came up about thirty days after they were sown. The remaining kinds which vegetated were as follows:-a species of Malva, a Euphorbia, and Galega sibirica, gathered in 1836; Tomates, of 1837; Lupinus hirsutus, of 1842; Dianthus chinensis, of 1843: Mesembryanthemum pomeridianum, Lupinus Cruikshanksii, Nolana paradoxa, Helichrysum repandum, Amaranthus speciosus, Datura Tatula, Medicago pentacycla, and Dianthus superbus, of 1844, and several of 1845, the whole of which came up.

Amongst those of uncertain date (from 1833 to 1842, the seeds collected in those years having been mixed) a few seeds of Celosia cristata, yellow, Lathyrus sylvestris, Malva diversiloba, Calandula stellata, Onopordon acanthium, Sisyrinchium laxum, Scrophularia peregrina, and Silene armeria came up.

1847.

L

Professor Balfour has also contributed twenty-nine kinds of seeds of various dates, in small quantities, and which have consequently been sown only at Oxford.

The sowing of the seeds has been performed under similar circumstances to those detailed in the Report for 1846.

The results are registered in the following Table :

On the Turbine or Horizontal Water-Wheel of France and Germany. By JOSEPH GLYNN, F.R.S., M. Inst. C.E. &c.

Ar the meeting of the British Association in Glasgow, in 1840, Professor Gordon brought the subject of the Turbine before the Mechanical Section; he had seen it in use on the Continent, and the account he gave of its utility and value induced the Section to recommend the appointment of a committee, consisting of Professor Gordon, Mr. Smith of Deanston, and Mr. Fairbairn of Manchester, to inquire and report to the Association the merits and defects of this machine, and the difference between the power and effect of the water-fall applied to it.

No grant of money was asked for, and no report has been made. Indeed, to have obtained the requisite facts and materials for such a report, a journey to France and Germany would have been necessary, as there have been no machines of this kind yet erected in England; nor was there until recently any work in the English language treating upon them, although there were several both in French and German.

Lately, however, Sir Robert Kane, whose excellent book on the industrial resources of Ireland is so well known, has translated from the German of Moritz Ruhlmann a work on horizontal water-wheels, turbines, or whirlwheels, which is rendered valuable to practical men by Professor Kane's notes and observations.

In order that the subject of this paper may be better elucidated and traced from its first elements, it may be proper to notice the philosophical toy which figures in many works on hydrostatics and hydraulics as Dr.