WOOD DISTILLATION. 
lignin is effected before distillation, so that a mixture of all these by- 
products is obtained. In wood the proportion between these two essen- 
tial constituents is variable, so that the wood distillate will also vary. 
DisTILLATION. 
The distillation is carried out in large chambers whose construction 
varies at different works, while the condensation of the distillate is 
effected in water-cooled coils by the usual methods. A suitable quan- 
tity of the wood is introduced into the distillation chamber and then 
heated to about 270 deg. C. At this point the reaction becomes 
exothermic, and so much heat is evolved that further heating is unneces- 
sary, and the reaction proceeds of itself. The liquid distillate which 
is collected is known as crude pyroligneous acid, and it contains all 
the by-products which have subsequently to be separated. But not all 
the products of distillation are able to be condensed. A considerable 
proportion are gaseous, and these are used in the heating of the distil- 
lation retort, thereby effecting a saving of fuel. The residue in the 
distillation chamber is wood charcoal, and is ground up and is then 
ready for the market. 
The following indicates the average amounts of the crude products 
obtained by the dry distillation :— : 
Carbon (wood charcoal) is .. 26.0 per cent. 
Crude pyroligneous acid sy ne ee LA DIG e tala 
Non-condensed gases . cig AO api oy 
Of these, the crude acid is the most important as regards the dyeing 
industry. It consists of :— - 
Acetic acid Bei lp .. 7.0 per cent. 
Methyl alcohol and acetone .. Ay ts, BS Oe 
Tar and impurities .. ff peed SOs Olga, 
Water a te fies tee, rer ey 
so that it can be readily seen that acetic acid is its most important 
constituent. 
In working up the crude acid, the distillate is first allowed to settle, - 
and it can then be separated from a large proportion of the tar. But 
not all, since some of the tar exists in a state of an emulsion. Com- — 
plete separation is effected in the next process in which the crude pyro- 
ligneous acid is distilled. The distillate is generally absorbed or added 
to milk of lime. This serves to fix the acetic acid as calcium acetate, 
and also hydroylses any esters that may have formed. Methyl acetate, 
pesel is always present, is decomposed into methyl alcohol and acetic 
acld. : ; 
Limes Liquors. — 
The lime liquors are again distilled. The calcium acetate, being non- 
volatile, remains in the “still” residue, while the distillate contains 
the methyl] alcohol, acetone, and a few other substances. Acetic acid, 
calcium acetate, and sodium acetate are obtained by treatment of this 
“still” residue. The liquid is concentrated and finally evaporated to 
dryness. A golid is obtained, which is known as brown acetate of lime. 
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