THE COLOURING MATTERS OF SANDALWOOD AND OTHER DYE-WOODS.
In addition to the dye-woods in more common use, the tropics furnish
a number of woods which contain fine colouring matters, but which are
only in restricted use, either on account of their cost or because they
are not always to be bought. To these belong the camwood or barwood of
Madagascar, the East Indian sandalwood, and other woods which have not
yet been used for colouring purposes even in the tropics.
The most commonly used of the rarer dye-woods is sandalwood, obtained
from _Pterocarpus santalinus_. It is garnet red in colour, sinks in
water, and produces a fine red meal, which rapidly becomes brown in
air owing to oxidation of the colouring matter. According to recent
researches, sandalwood contains two colouring matters, one obtained
from the other by oxidation. Only one of these, santalin, is known
with certainty. Sandalwood contains about 16 per cent. of santalin,
which when pure forms a crystalline powder, differing from other
wood colouring matters in being almost insoluble in water. Up to the
present it has only been used in dyeing to obtain handsome and fast red
colours. From it very bright lakes may be obtained, which may be used
equally as well as the red wood lakes. The aluminium and tin lakes are
especially fine. The extract of sandalwood is obtained by boiling very
fine chips with water, then adding alcohol and leaving the mixture.
When stannic chloride or alum, or a mixture of the two, is added to the
solution of the colouring matter a red precipitate is produced which,
after washing and drying, furnishes a bright red lake.