IHR f2w
trichloro-ethane (D.D.T) and copper naphthenate. These are dissolved in suitable organic
solvents like naphtha, or in petroleum products such as kerosene, spirit, etc. The treated timber
can be painted, waxed or polished.
e e is used for protection of veneers, plywood and light lumbers
against decay by acetylation. They are treated with acetic anhydride vapour, which minimises
swelling and improves resistance to decay and attack by insects.
&&2@)!2QA are odourless organic or inorganic salts and are adopted
for inside locations only. If applied over outside surfaces, the salts can be leached by rain-
water. Examples of leachable (3A-water soluble) type of preservatives are zinc chloride, boric
acid (borax), etc. Zinc chloride, sodium fluoride and sodium-penta-chloro-phenate are toxic to
fungi. These are expensive and odourless (except for sodium-penta-chloro-phenate). Benzene-
hexa-chloride is used as spray against borers. Boric acid is used against Lyctus borers and to
protect plywood in tea chests.
Some of the other water soluble preservatives are fixed (3B-water soluble) type and are as
follows.
g(( E E ( is made of three chemicals.
Arsenic-pentaoxide As 2 O 5 .2H 2 O 1 part
Copper sulphate CuSO 4 .5H 2 O 3 parts
Sodium or potassium dichromate (Na or K) 2 Cr 2 CO 7 4 parts
The preservative is in the form of a powder and is used with water. Six parts of this powder
is mixed with 100 parts by weight of water. The solution is applied in two coats. The timber is
then allowed to dry for six weeks. This treatment renders the timber immune to the attacks of
white ants and is known as AsCu treatment.
eE( E 2 (
Chromic acid 1.7 parts
Copper sulphate 50 parts
Sodium dichromate 48.3 partsg E/2 2 (
chloride 1 part
Sodium or potassium dichromate 1 partg(( E E 2 (
Boric acid 1.5 parts
Copper sulphate 3 parts
Sodium or potassium dichromate 4 partsE E 2 (
Arsenious trioxide 3 parts
Zinc oxide 2 parts
Acetic acid Just to keep the above in solution
under operating conditions