192 EXTRACTING COLOURING FROM DYE-WOODS. 
duced to powder, it absorbs so much water that a great 
quantity of liquid is lost, and the shavings being rather thick, 
the water cannot readily penetrate, for which reason the 
time of boiling is very much prolonged. 
Notwithstanding these three long boilings, if the same 
wood be boiled a fourth time, a liquid pretty well coloured is 
obtained; which clearly shows that all the coloring matter 
has not been extracted. 
Besides this, when decoctions of logwood are required in 
large quantities, very large vessels and extensive premises 
are necessary, as well as several furnaces, in order to pro- 
duce a sufficient quantity : for the wood, when in shavings, 
is very bulky without being heavy, and large boilers are re- 
quired for making a decoction from 50 lbs. of shavings, with 
the necessary quantity of water. Several boilers must, 
therefore, be employed, otherwise the fire must be kept up 
day and night. 
I will here describe, en passant, for the benefit of those 
persons who have not many furnaces, but who have a steam- 
pipe at command, a method which I have employed for 
some time to make decoctions in great quantities, and which, 
I think, I can recommend in this instance. 
A large high narrow vat, capable of containing about 
from 100 to 150 lbs. of wood shavings, is mounted upon a 
stand or framing, and furnished with a cock below, in order 
to draw off the liquor. At a short distance above the cock, 
inside the vat, a false bottom or diaphragm, pierced with 
holes very close to each other, is fixed, in order to leave a 
space at the bottom to prevent the wood from clogging up 
the cock, and stopping the flow of the liquor. A steam-pipe, 
about one-third o fan inch in diameter, is carried to the 
bottom of the vat, which is filled with shavings. It is covered 
with a cloth and a cover, which is weighed, in order to 
prevent the steam from issuing out in too great abundance. 
The shavings must not be heaped up more than in the com- 
mon boilers. In this state, steam is allowed to flow in for 
