a weighed quantity of the sample, and comparing the depth and solidity of the colours with those produced by the same weight of another sample of known quality, and even this method may lead to uncertain results, if practised on too small a scale. The Paluds, which is the most esteemed of the Avignon madders, has a dark red hue, whereas the other kinds have naturally a yellow, reddish-yellow or brownish-yellow colour. Nevertheless, means have been devised of communicating to the latter the desired reddish tinge, which, therefore, no longer serves as a test. A method formerly employed to ascertain the comparative value of a number of samples of madder consisted in placing a small quantity of each sample on a slate, pressing the heaps flat with some hard body, and then taking them to a cellar or other damp place. After 10 or 12 hours they were examined, and that which had acquired the deepest colour, and increased the most in volume was considered the best. This method led, however, to so many frauds on the part of the dealer, for the purpose of producing the desired effect, that it is no longer resorted to. Madder is sometimes adulterated with sand, clay, brick-dust, ochre, saw-dust, bran, oak-bark, logwood and other dye-woods, sumac and quercitron bark. Some of these additions are difficult to detect. Such as contain tannin may be discovered by the usual tests, since madder contains naturally no tannin. If the material used for adulteration be of mineral nature, its presence may be discovered by incinerating a weighed quantity of the sample. If the quantity of ash which is left exceeds 10 per cent. of the material employed, adulteration may be suspected. The ash obtained by incinerating pure madder consists of the carbonates, sulphates, and phosphates of potash and soda, chloride of potassium, carbonate and phosphate of lime, phosphate of magnesia, oxide of iron and silica. If a considerable amount of any other mineral constituent is found, it is certainly due to adulteration.

There is probably no subject connected with the art of dyeing which has given rise to so much discussion as the composition of madder, and the chemical nature of the colouring matters to which it owes its valuable properties. The subject has engaged the attention of a number of chemists, whose labours, extending over a period of about fifty years, have thrown considerable light on it. Nevertheless, the conclusions at which they have severally arrived do not perfectly agree with one another, nor with the views entertained by the most intelligent of those practically engaged in madder dyeing. The older investigators supposed that madder contained two colouring matters, one of which was tawny, and the other red. Robiquet was the first chemist who asserted that it contained two distinct red colouring matters, both of which contributed to the production of the dyes for which madder is employed; and his views, though they were at the time of their promulgation strongly objected to by some of the most eminent French dyers and calico-printers, still offer probably the best means of explaining some of the phenomena occurring during the process of madder dyeing. The two red colouring matters discovered by Robiquet were named by him Alizarine and Purpurine, and these names they still retain. Several crystallised yellow colouring matters have been discovered by other chemists; but the only one which exists ready-formed in the madder of commerce is the Rubiacine of Schunek, and this substance may also be taken as the type of the whole class, the members of which possess very similar properties. Among the other organic substances obtained by different chemists from madder, two resinous colouring matters, sugar, a bitter principle, a peculiar extractive matter, pectin, a fermentative nitrogenous substance, and malic, citric, and oxalic acids, may be mentioned.

When madder is extracted with boiling water, a dark brown muddy liquid, having a taste between bitter and sweet, is obtained. On adding a small quantity of an acid to this liquid, a dark brown precipitate is produced, while the supernatant liquid becomes clear, and now appears of a bright yellow colour. The precipitate consists of alizarine, purpurine, rubiacine, the two resinous colouring matters, pectic acid, oxidised extractive matter, and a peculiar nitrogenous substance. The liquid filtered from this precipitate contains the bitter principle and the extractive matter of madder, as well as sugar and salts of potash, lime and magnesia. No starch, gum, or tannin can be detected in the watery extract. After the madder has been completely exhausted with boiling water, it appears of a dull red colour. It still contains a quantity of colouring matter, which cannot, however, be extracted with hot water, or even alkalies, since it exists in a state of combination with lime and other bases, forming compounds which are insoluble in those menstrua. If, however, the residue be treated with boiling dilute muriatic acid, the latter dissolves a quantity of lime, magnesia, alumina, and peroxide of iron, as well as some phosphate and oxalate of lime, which may be discovered in the filtered liquid; and if the remainder, after being well washed, be treated with caustic alkali, a dark red liquid is obtained, which gives with acids a dark reddish-brown precipitate consisting of alizarine, purpurine, rubiacine, resin, and pectic acid. That portion of the madder left after treatment with hot water, acids, and alkalies, consists almost entirely of woody fibre.

A short description of some of the substances just mentioned will not be out of place here, as it may assist in rendering the process of dyeing with madder more intelligible.

The most important of these substances is alizarine, since it forms the basis of all the finer and more permanent dyes produced by madder. The matière colorante rouge of Persoz and the madder-red of Runge also consist essentially of alizarine, mixed with some impurities. Robiquet first obtained it in the form of a crystalline sublimate, by extracting madder with cold water, allowing the liquid to gelatinise, treating the jelly with alcohol, evaporating the alcoholic liquid to dryness and heating the residue; and since the application of heat seemed to be an essential part of his process, it was for a long time doubted whether alizarine was contained as sach in madder, and was not a product of decomposition of some other body. It was proved, however, by the experiments of Schunek that it does in reality pre-exist in the ordinary madder of commerce, though not in the fresh root when just taken out of the ground. It has the following properties: - It crystallises in long, transparent, lustrous, yellowish-red needles. These needles when heated to 212° F. lose their water of crystallisation and become opaque. At about 420° F. alizarine begins to sublime, and if carefully heated may be almost entirely volatilised, only a little charcoal being left behind. The sublimate obtained by collecting the vapours consists of long, brilliant, transparent, orange-coloured crystals, which are pure anhydrous alizarine. If madder, or any preparation or extract of madder, be heated to the same temperature, a sublimate of alizarine is also obtained, but the crystals are then generally contaminated with drops of empyreumatic oil, produced by the decomposition of other constituents of the root. This oily matter may, according to Robiquet, be removed by washing the crystals with a little cold alcohol. Alizarine is almost insoluble in cold water. It is only slightly soluble in boiling water, and is deposited, on the solution cooling, in yellow crystalline flocks. When the water contains large quantities of acid or salts in solution, it dissolves very little alizarine, even on boiling. The colour of the solution is yellowish when it is quite free from alkalies or alkaline earths. Alizarine dissolves much more readily in alcohol and ether than in water; the solutions have a deep yellow colour. Alizarine is decomposed by chlorine, and converted into a colourless product. It is also decomposed by boiling nitric acid, the product being a colourless, crystallised acid, phthalic acid, the same that is formed by the action of nitric acid on naphthaline. Alizarine dissolves in concentrated sulphuric acid, yielding a yellow solution, which may be heated to the boiling point without changing colour and without any decomposition of the alizarine, which is precipitated unchanged on the addition of water. Alizarine dissolves in caustic alkalies with a splendid purple or violet colour, which remains unchanged on exposure of the solutions to the air. The ammoniacal solution, however, loses its ammonia entirely on being left to stand in an open vessel, and deposits its alizarine in the form of shining prismatic crystals, or of a crystalline crust. The alkaline solutions give with solutions of lime and baryta salts precipitates of a beautiful purple colour, with alumina salts a red, with iron salts a purple precipitate, and with most of the salts of metallic oxides precipitates of various shades of purple. The affinity of alizarine for alumina is so great, that if the compound of the two bodies be treated with boiling caustic potash lye, it merely changes its colour from red to purple without being decomposed. Alizarine is not more soluble in boiling alum liquor than in boiling water. The chemical formula of anhydrous alizarine is probably CHO, and 100 parts contain therefore by calculation 69.42 of carbon, 4.13 of hydrogen, and 26.45 of oxygen.

If alizarine in a finely divided or, what is still better, in a freshly precipitated state, be suspended in distilled water, and a piece of calico printed with alumina and iron mordants of different strengths be plunged into it, the latter, on gradually heating the bath, become dyed. The process is necessarily a slow one, because alizarine is only slightly soluble in boiling water, and as the mordants can only combine with that portion actually in solution, a constant ebullition of the liquid must be kept up, in order to cause fresh portions of colouring matter to dissolve in the place of that portion taken up by the mordants. A very small proportional quantity of alizarine is required in order to dye very dark colours, but it is absolutely necessary that the bath should contain no trace of either acid or base, since the former would combine with the mordants, and the latter with the alizarine. When the process is complete the alumina mordant will be found to have acquired various shades of red, while the iron mordant will appear either black or of different shades of purple, according to the strength of the mordant employed. These colours are as brilliant and as permanent as those obtained from madder by means of a long and complicated process. Nevertheless, the red is generally found to have more of a purplish hue, and the black to be less intense than when madder or its preparations are employed. On the other hand, if one of the finer madder colours which are

produced on calico, such as pink or lilac, be examined, the colours are found to contain, in combination with the mordants, almost pure alizarine. Hence it may be inferred, that alizarine alone is required for the production of these colours, and that the simple combination of this colouring matter with the mordants is the principal end which is to be attained by the dyer in producing them.

Purpurine, the other red colouring matter of madder, with which the matière colorante rose of Gaultier de Claubry and Persoz, and the madder-purple of Runge, are substantially identical, can hardly be distinguished by its appearance from alizarine, which it also resembles in most of its properties. It crystallises in small orangecoloured or red needles. When carefully heated it is almost entirely volatilised, yielding a sublimate of shining orange-coloured scales and needles. It is slightly soluble in boiling water, giving a pink solution. It is more soluble in alcohol than in water, the solution having a deep yellow colour. It dissolves in concentrated sulphuric acid, and is not decomposed on heating the solution, even to the boiling point. It is decomposed by boiling nitric acid, and yields, like alizarine, phthalic acid. It is distinguished from alizarine, by its solubility in alum liquor. When treated with a boiling solution of alum in water, it dissolves entirely, yielding a peculiar opalescent solution, which appears of a bright pink colour by transmitted light, and yellowish by reflected light. The solution deposits nothing on cooling, but on adding to it an excess of muriatic or sulphuric acid, it becomes colourless, and the purpurine falls down in yellow flocks. On this property depends the method of separating it from alizarine. The compounds of purpurine with bases are mostly purple. It dissolves in alkalies with a bright purplish-red or cherry-red colour. If the solution in caustic potash or soda be exposed to the air, its colour changes gradually to reddish-yellow, and the purpurine contained in it is decomposed, a characteristic which also serves to distinguish purpurine from alizarine, the alkaline solutions of which are not changed by the action of oxygen. The composition of purpurine approaches very near to that of alizarine, but its chemical formula is unknown. It communicates to calico, which has been printed with various mordants, colours similar to those imparted by alizarine, but the red is more fiery, and the black more intense than when alizarine is employed. On the other hand, the purple dyed by means of purpurine has a disagreeable reddish tinge, and presents an unpleasant contrast with the beautiful purple from alizarine. The name of this colouring matter is therefore very inappropriate, and is calculated to mislead. The colours dyed with purpurine are less stable than those dyed with alizarine, they are less able to resist the action of soap and other agents than the latter. Hence, very little purpurine is found in combination with the mordants, in such madder colours as have undergone a course of treatment with alkalies and acids, after having been dyed; indeed, the principal object of this treatment appears to be the removal of this and other substances, so as to leave compounds of alizarine only on the fabric. Purpurine seems to abound more in the lower, stronger qualities of madder than in the finer. To this cause, Robiquet chiefly ascribed the superiority of the latter in dyeing fast colours, and no better way of accounting for it has hitherto been suggested. Parparine forms the basis of the red pigment called madder lake.

Rubiacine is the name which has been applied to a yellow crystallised colouring matter contained in madder. It coincides in most of its properties with the madder-orange of Runge. It crystallises in greenish-yellow lustrous scales and needles. When heated it is entirely volatilised, yielding a crystalline sublimate. It is only slightly soluble in boiling water, but more soluble in boiling alcohol, from which it crystallises on cooling. It dissolves in concentrated sulphuric acid, and is not decomposed on boiling the solution. It also dissolves in boiling nitric acid without being decomposed. It dissolves in caustic alkalies with a purple colour. Its compounds with earths and metallic oxides are mostly red. When treated with a boiling solution of pernitrate or perchloride of iron it dissolves entirely, yielding a brownish-red solution, which deposits nothing on cooling, but gives, on the addition of an excess of muriatic acid, a yellow flocculent precipitate, consisting of a peculiar acid, called rubiacic acid.

Two amorphous resinous colouring matters, forming brownish-red compounds with bases, have also been obtained from madder. Both are very little soluble in boiling water. One of them is a dark brown, brittle, resin-like substance, very easily soluble in alcohol, which melts at a temperature a little above 212° F. The other is a reddish-brown powder, less soluble in alcohol than the preceding. These two colouring matters, together with rubiacine, constitute probably the tawny or dur colouring matter of the older chemists. They do not contribute to the intensity of the colours dyed with madder, and exert a very prejudicial effect on the beauty of the dyes. If printed calico be dyed with a mixture of alizarine, and any one of these three colouring matters, the colours are found to be both weaker and less beautiful than when alizarine is employed alone. The red acquires an orange tinge, and the purple a reddish hue, whilst the black is less intense, and the parts of the calico which should remain white are found to have a yellowish colour. Hence it is of importance to the dyer that their effect should be counteracted as much as possible, by preventing them either from dissolving in the dye-bath or from attaching themselves to the fabric.

The other constituents of madder possess no interest in themselves, but may become of importance in consequence of the effects which they produce during the process of dyeing. The pectine, in the state in which it exists in the root, is probably an indifferent substance, but in consequence of the ease and rapidity with which it passes into pectic acid, it may in dyeing act very prejudicially by combining with the mordants and preventing them taking up colouring matter. The extractive matter of madder, when in an unaltered state, produces no injurious effects directly; but by the action of oxygen, especially at an elevated temperature, it acquires a brown colour and then contributes, together with the rubiacine and the resinous colouring matters, in deteriorating the colours and sullying the white parts of the fabric. The extractive matter, when in a state of purity, has the appearance of a yellow syrup like honey, which is easily soluble in water and alcohol. When pure it is not precipitated from its watery solution by any earthy or metallic salt, but if the solution be evaporated in contact with the air, it gradually becomes brown, and then gives an abundant brown precipitate with sugar of lead. When its watery solution is mixed with muriatic or sulphuric acid and boiled, it becomes green and deposits a dark green powder. Hence this extractive matter has, for the sake of distinction, been called Chlorogenine, and Rubichloric Acid. The bitter principle of madder will be referred to presently. The Xanthine of Kuhlmann, and the madder-yellow of Runge are mixtures of the extractive matter and the bitter principle. The sugar contained in madder is probably grape sugar. It has not hitherto been obtained in a crystallised state, but it yields by fermentation alcohol and carbonic acid, like ordinary sugar. The woody fibre which is left after madder has been treated with various solvents until nothing more is extracted, always retains a slight reddish or brownish tinge from the presence of some colouring matter which cannot be completely removed, and seems to adhere to it in the same way as it does to the cotton fibre of unmordanted calico.

There is a question connected with the chemical history of madder which must not be passed over in silence, since it is one which possesses great interest, and may at some future time become of great importance, viz. the question as to the state in which the colouring matters originally exist in the root. It has long been known, that when ground madder is kept tightly packed in casks for some time, it constantly improves in quality for several years, after which it again deteriorates; and it was always supposed that this effect was due to some process of slow fermentation going on in the interior of the mass, an opinion which seemed to be justified by the evident increase in weight and volume, and the agglomeration of the particles which took place at the same time. Nevertheless the earlier chemical examinations of madder threw no light whatever on this part of the subject, since the red colouring matters were found to be very stable compounds, not easily decomposed except by the action of very potent agents, so that when once formed it seemed improbable that they would be at all affected by any mere process of fermentation. Hence some chemists were led to the conclusion that the improvement which takes place in the quality of madder on keeping is caused by an actual formation of fresh colouring matter. A very simple experiment may indeed suffice to prove that the whole of the colouring matter does not exist ready formed, even in the article as used by the dyer. If ordinary madder be extracted with cold water, the extract after being filtered has generally an acid reaction, and cannot contain any of the colouring matters, since these are almost in. soluble in cold water, especially when there is any acid present. Nevertheless the extract when gradually heated is found capable of dyeing in the same way as madder itself. If the extract be made tolerably strong, it possesses a deep yellow colour and a very bitter taste; but if it be allowed to stand in a warm place for a few hours, it gelatinises, and the insoluble jelly which is formed is found to possess the whole of the tinctorial power of the liquid, which has also lost its yellow colour and bitter taste. Hence, it may be inferred that the substance which imparts to the extract its bitter taste and yellow colour is capable also of giving rise to the formation of a certain quantity of colouring matter.

In 1837 a memoir was published by Decaisne, containing the results of an anatomical and physiological examination of the madder plant, results which were considered so important that a prize was awarded to the author by the Royal Academy of Sciences of Brussels. This investigation led the author to the conclusion, that the cells of the living plant contain no ready-formed red colouring matter, but are filled with a transparent yellow juice, which on exposure to the atmosphere becomes reddish and opaque in consequence of the formation of red colouring matter. Hence he inferred that the insoluble red colouring matter was simply a product of oxidation of the soluble yellow one, and that, consequently, the more complete the exposure of the triturated root to the atmosphere, the greater would be its tinctorial power; and he even went so far as to assert that all the proximate principles obtained from the root were derived ultimately from one single substance contained in the whole plant. That the fresh roots, before being dried, do indeed contain no colouring matter capable of imparting to mordants colours of the usual appearance and intensity, may be proved by the following experiment: - If the roots, as soon as they are taken out of the ground, are cut into small pieces as quickly as possible, and then extracted with boiling spirits of wine, a yellow extract is obtained which, after being filtered and evaporated, leaves a brownish-yellow residue. Now this residue on being redissolved in water is found incapable of imparting to mordants any but the slightest shades of colour; and, on the other hand, the portion of the root left after extraction with spirits of wine, on being subjected to the same test as the extract, is found to possess as little tinctorial power as the latter. If, however, the roots, instead of being treated with spirits of wine, are macerated in water, the liquor on being gradually heated dyes the usual colours as well as ordinary madder. Hence it may be iuferred that by means of alcohol the colour-producing body of the root may be separated from the agent which, under ordinary circumstances, is destined to effect its transformation into colouring matter, the one being soluble and the other insoluble in that menstruum. It was by this and other similar facts that Schunck was led to an examination of this part of the subject. He infers from his experiments that the colourproducing body of madder is identical with its so-called bitter principle, to which he has given the name of Rubian. This body, when pure, has the following properties: - It is an amorphous, shining, brittle substance like gum, dark brown and opaque in mass, but yellow and transparent in thin layers. Its solutions are of a deep yellow colour, and have an intensely bitter taste. It is easily soluble in water and alcohol. The watery solution turns of a blood-red colour, on the addition of caustic and carbonated alkalies, and gives dark red precipitate with lime and baryta water. The solution gives a copious light red precipitate with basic acetate of lead, but yields no precipitate with any other metallic salt. On trying to dye with rubian in the usual manner, the mordants assume only the faintest shades of colour. If, however, the watery solution be mixed with sulphuric or muriatic acid and boiled, it gradually deposits a quantity of insoluble yellow flocks, which after being separated by filtration and well washed, are found to dye the same colours as those obtained by means of madder. In fact, these flocks contain alizarine, to which they owe their tinctorial power, but they also contain a crystallised yellow colouring matter, similar to, but not identical with rubiacine, as well as two resinous colouring matters, which Schunek has named Verantine and Rubiretine, and which are probably identical with the resinous colouring matters before referred to as being obtained from ordinary madder. The liquid filtered from the flocks contains an uncrystallisable sugar, similar to that which is obtained from madder itself. Rubian is not decomposed by ordinary ferments, such as yeast and decomposing casein; but by extracting madder with cold water, and adding alcohol to the extract, a substance is precipitated in pale red flocks, which possesses in an eminent degree the power of effecting the decomposition of rubian. If a watery solution of the latter be mixed with some of the flocculent precipitate (after having been collected on a filter, and washed with alcohol), and then left to stand in a warm place for some hours, the mixture is converted into a light brown jelly, which is so thick that the vessel may be reversed without its falling out. This jelly when agitated with cold water communicates to the latter very little colour or taste, proving that the rubian has undergone complete decomposition by the action of the flocculent substance or ferment added to its solution. The cold water, however, extracts from the gelatinous mass a quantity of sugar, while the portion left undissolved contains alizarine, verantine, rubiretine, and a crystalline yellow colouring matter, besides a portion of undecomposed ferment. Rubian, therefore, by the action of strong mineral acids and of the peculiar ferment of madder, is decomposed, yielding sugar and a variety of colouring matters, the principal of which is alizarine. It appears, therefore, that these colouring matters are not originally contained as such in the root, but are formed by the decomposition of one parent substance, which alone is produced by the vital energies of the plant. In addition to this substance, the plant also contains another, which possesses the property of rapidly effecting the decomposition of the first. The two are, however, during the living state of the plant, prevented from acting on one another, either in consequence of their being contained in different cells, or because the vital energies of the plant resist the process of decomposition. During the drying and grinding of