Indian Forest Records. 
[VOL. III. 
88 
Description of the Process and Plant required. 
The Open Tank process consists in either immersing timber for a 
varying period of time in a hot solution of an antiseptic fluid, or of heating 
the timber in a hot bath and then quickly transferring it to a cold bath 
containing the preservative, or again of treating the timber in a hot 
antiseptic solution and allowing it to remain in the bath while the fluid 
cools down. The necessary apparatus consists of a tank, capable of 
withstanding heat and fitted either with coils of pipes for heating the 
solution, or capable of being placed over an open hearth. Such a plant 
is not of an expensive nature and is at the same time easily moveable, 
therefore it possesses great advantages over the large and costly apparatus 
necessary for hydrostatic or pneumatic impregnation. 
Method of Treatment. 
The treatment, as now carried out, consists in the immersion of the 
timber for a period varying from 15 minutes to 24 hours and more, in a 
solution heated to a temperature of 7 7° C. and over. The temperature and 
period of immersion vary according to the density and anatomical struc¬ 
ture of the wood; as an example, a piece of Pine or Boswellia serrata 
of 2" x 2" x 18" becomes saturated throughout by an antiseptic such 
as Carbolineum oil, after an immersion of 15 minutes, at a temperature 
of 77° C., while the solution only penetrates to the depth of one-eighth 
of an inch along the fibre and one-sixteenth of an inch across the fibre 
in the case of closer grained woods, such as the Dipterocarps, indica¬ 
ting that a more drastic treatment is required. 
• 
Theory on which the Process is based. 
The theory underlying the Open Tank process is based on the fact 
that a vacuum exists in seasoned timber and that it is further increased 
by immersion in a hot bath, in that the air on being heated expands 
and is expelled from, the wood. Now, after the timber has been immer¬ 
sed in a hot solution if allowed to stay in the liquid as it cools down, 
on the temperature dropping the vacuum comes into play and as the 
wood is immersed, instead of the air again filling the cellular spaces, 
its place is taken by the antiseptic fluid. 
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