105
OF ENGINEERING FOEMULÆ.
Impregnation of Timber—continued.
of timber, for a period varying from f of an hour
to 2| hours.
8 lbs. or ‘8 gallon should be the quantity
absorbed.
10 lbs. or 1 gallon for marine works.
Oak will not absorb more than 6 lbs.
Red pine will absorb 15 or 16 lbs.
Mr. Bethell prefers to use for creosoting timber
with the outer layers intact, because the outer
wood absorbs the creosote more readily, and sap-
wood fully impregnated is more durable than
heart-wood unimpregnated.
Creosoting about doubles the life of sleepers if
properly performed, and is uniformly satisfactory.
IMPREGNATION WITH METALLIC SALTS.
The result of impregnation with metallic salts
has not in all cases been satisfactory.
Burnett's Chloride of Zinc, with 25 to 40 per
cent, of metallic zinc (3 parts of hydrochloric acid
to 1 of zinc). The mixture is diluted with from
30 to 60 parts of water, aud applied under pressure
of 100 to 120 lbs. per square inch for fifteen
minutes.
Kyan’s Chloride of Mercury, diluted with 150
parts of water, applied cold without pressure.
Makgeky’s Sulphate of Copper, diluted with 40
to 50 parts of water, applied with pressure varying
from 15 to 30 lbs. per square inch, for six or eight
hours.
Paine’s Sulphate of Iron and Sulphate of Barium.
This appears to give rise to a slow decomposition
and destruction of the fibres of the wood.