122. If the roots of madder be examined with a mi croscope, the interior part is observed to contain a con siderable proportion of specks of a bright red colour ; but the ligneous part which surrounds these, as well as the bark, abounds with a brownish yellow colouring mat ter, which tends greatly to degrade the red that madder would otherwise afford. The pernicious effects of this yellow matter, when madder is used as a dye, may in some degree be avoided, by extracting the colouring matter in water which is but moderately warm, the yel low matter being but imperfectly dissolved so long as the heat is below the boiling point. The outer bark and ligneous parts are also more easily pounded than the pa rachymatous parts, to which the red colour is more im mediately attached, and, on this account, a separation may, to a certain extent, be effected by mechanical means. This separation established among the French dyers the distinction of madder into robee, ?nis-robee, and course. After the first operation of the mill, the madder is passed through a sieve with a cover fitted to it, and, by this means, what is called the short madder, which is used for inferior colours, is obtained ; the remainder be ing again ground and sifted, produces the mis-robee ; and a third operation affords the robee or finest madder.
123. Water of the ordinary temperature of the at mosphere may be made to dissolve almost all the red colouring matter from madder ; but for this purpose it must be employed in large quantity ; and the colour is more beautiful when the solution is obtained by cold than by hot water. Alkalies increase the solving power of water, particularly with respect to the yellow mat ter. The residuum is very inconsiderable, so that mad. der appears to consist almost wholly of colouring mat ter. The latter portinnc of the extract, which seems to be chiefly yielded by the ligneous and cortical parts, is fawn-coloured.
124. The red colouring matter of madder is soluble in alcohol, and, on evaporation, a deep red residuum is left. Fixed alkali forms, with this solution, a violet ; the sulphuric acid, a fawn-coloured ; and the sulphate of potash, a fine red precipitate. Precipitates of various shades may be obtained by alum, nitre, chalk, acetite of lead, and muriate of tin. The infusion of the best Zea land madder, a solution of alum having been previously added to it, affords, with alkaline carbonates, a lake of a blood-red colour, which has greater or less intensity, ac cording to the quantity of alum that has been dissolved in it. This lake is transparent in oil, but with water it is opaque, and destitute of beauty. Calcareous earth precipitates a more d..rk and brown-coloured lake than alkalies, particularly if employed in the form of lime water. The carbonate of magnesia produces with alum a clear blood-red extract, which readily dissolves in wa ter.
125. D'Ambourney and some others pretend, that the roots of madder may be used with greater advantage when they are freshly gathered, than after they have been kept for some time, and reduced to the state of powder. This assertion, however, is by no means coun tenanced by the general experience of practical dyers, who find, that, if properly dried, and carefully preserved from moisture, madder improves by kerping, at least during the two first years.
126. The colour yielded by the chat, chayaver of the Tamils, which Dr Roxburgh has ascertained to be a species of oldenlipulta, is nearly allied to that madder. This plant is a small biennial, rarely a triennial, growing spontaneously on light sandy soils, and extensively culti sated on the Coromandel coast. The cultivated roots are et y slender, and from one to two feet in length the tt 11.1 are shorter, and irld more colouring matter, is also of a superior quality. T .
he colour, which of an orange hue, seems to reside almost entirely in the hark of the roots.
127. The chAy root is said to be extensively employ ed as n die in India but the colours obtained from it, by those who have examined its properties in this coun try, do not warrant us to recommend its importation. Dr Bancroft states. that the best specimens of it which he could procure, did not seem, in any instance, to yield a colour superior to that of madder, but, in gene ral. greatly inferior both in beauty and durability. With the solutions of tin, it produced a very bright and last ing red on wool ; though, like that of madder, it incli ned too much to the orange. With the oxides of iron it produced nothing darker than drab colours, either upon wool or cotton. Ilroad cloth dyed without any basis, ac quired from chat' root a brownish red, which was nei ther so bright nor so durable as that which it assumes in the same way from madder.
128. The colouring matter yielded by the roots of ga lium, a genus of plants belonging to the same order as the preceding, differs but little from that of madder ; on ly when the brown external covering of the root is re moved, the colour which it imparts to wool is somewhat brighter, with an aluminous basis. The several species of galium chiefly employed in dyeing, are the follow ing : tinctorium, galium verum, galium go, galium sylvaticum, galium boreale, galium aparine. J he galium tinctorium is found in great abundance in the woods of North America, and its roots arc employed by the native inhabitants to dye porcupine quills of a red colour. The galiutn verum, yellow ladies' bed-straw, or cheese ;Tuning, affords a colour which is but little in ferior to the starlets dyed with cochineal. The roots, which afford the colouring matter, arc covered by a very dark hark, which must be removed, to prevent its affect ing the colour of the rest of the root. The dye thus obtained is employed by the people of the I highlands, and of sonic of the islands of Scotland, for giving a bright red to their woollen stuffs. The galium and the galium sylvaticum, yield a colour equally bright and lasting. The galium'boreale is said to afford a more brilliant red than any other spdcies. Its roots are used as a dye by the inhabitants of Switzerland. The galium aparine, con non rough ladies bed-straw, cleavers, or goose grass, also affords a red dye, but inferior to the last. Dr Bancroft has noticed a variety of other colour ing matters nearly allied to madder, but their properties are too unimportant to merit consideration in this work ; we shall therefore now proceed to make some observa tions on Brazil wood.