135. Barwood is obtained from Africa, principally from Angola, and is used as a dye. 1Vith the alumi nous mordant, it affords yellowish-brown reds to wool and cotton, though they are rather fugitive on the latter. The colour extracted from barwood may be saddened by employing solutions of iron along with it, either alone or conjointly with alum. The dark red, which is com monly seen upon the British imitations of East India silk handkerchiefs, is generally given by barwood and sul phate of iron.
136. Red saunders, the wood of a tree which is brought from Coromandel, is also used as a (lye. Its colouring matter is imperfectly soluble in water, even with the as sistance of potash or soda. Dr Bancroft found, that a diluted sulphuric acid acted very efficaciously in ex tracting the colour of this wood. Vogler says, that, by extracting the colour of red sounders by alcohol, he communicated to wool a colour almost equal to scarlet. A very bright and lasting orange may be given to broad-cloth, prepared, as usual, with alum and tartar, by employing equal portions of ground sumach and rasped saunders.
137. The wood of the Hxmatoxylon Campechianum affords a colouring matter, which is used very exten sively in dyeing. In commerce, it is known by the name of logwood, and also of India or Campeachy wood. Logwood is so heavy as to sink in water ; it possesses great hardness, and, by the compactness of its grain, takes a fine polish. Its prevailing colour is red, tinged with shades of orange, yellow, and brownish black, and is extracted in the same manner as that of Brazil-wood. Six quarts of distilled boiling water are capable of extracting almost all the colouring matter of one pound of logwood properly chipped. The decoc tion is of a yellow colour, and has a sweetish taste. If the decoction be made with common water, it exhibits a full red, or dark blood colour, probably by the action of the calcareous earth which common water usually con tains in combination with it ; but by adding to it sulphu ric, nitric, or muriatic acid, the yellow is restored.
138. When logwood is of a good quality, it yields from one-fifteenth to one-twentieth of its weight of pure colouring matter, soluble in water and in alcohol, if the decoction after being obtained has been speedily evapo rated to dryness ; but if an interval of several weeks has been allowed to intervene, or if the evaporation has been conducted slowly, and the decoction has been exposed to the sun and air, the colouring matter will absorb a large quantity of oxygen from the atmosphere, and become nearly insoluble in water, while the colours dyed from it will be more fugitive than those produced by a decoc tion recently prepared. In this respect it differs greatly
from Brazil wood.
139. Chips of logwood being boiled in water acidulat ed with sulphuric acid, afford a brownish yellow decoc tion, which communicates to wool a strong yellowish bright snuff colour, of considerable durability. Nitric acid being mixed with a decoction of logwood, produces a fine bright yellow, which becomes a yellowish brown by boiling, and imparts the same colour to wool. Cloth boiled with a decoction of logwood, slightly acidulated by muriatic acid, takes a brownish yellow colour. If a sufficient quantity of alum be added to a decoction of logwood, the colouring matter is all precipitated in combination with the alumine, of a purple or reddish violet colour. A sulphate of iron occasions a copious bluish black precipitate. All the solutions of tin pro duce purple or violet colours, and a complete precipita tion of the colouring matter. Sulphate of copper gives a purplish blue colour ; sulphate of pure zinc, a dark purple ; muriate of mercury, an orange red ; muriate of antimony, a beautiful crimson ; acetate of lead, a black precipitate, with a slight tinge of red ; lnuriate of barytes, a reddish purple ; muriate of magnesia, a yel low ; sulphate of lime, a purple ; arscniate of potash, a deep yellow.
140. The best and most permanent of the purple or violet colours obtained from logwood, are produced by mordants, principally composed of the solutions of till. In another part of this article, we shall describe the pro cess employed for dyeing in this way upon wool, a co lour which was very fashionable in France, upwards of thirty years ago, under the name of Prune de Monsieur. Wool dyed with logwood, and either sulphate of copper or verdigrise, acquires a blue colour, of little brightness and durability, which is chiefly recommended by its cheapness. The high price of indigo has of late ren dered this mode of dyeing blue very general, particular ly in France.