A manual of the principles and practice of road-making: comprising the location, construction, and improvement of roads, (common, macadam, paved, plank, etc.) and rail-roads. By W. M. Gillespie ...

254 IMPROVEIMENT OF THE SURFACE.
WOODEN PAVEMENTS.
Pavements formed of wooden blocks, Fig. 116.
usually hexagonal in shape, possess
many advantages. They cause little
resistance to draught; are almost en- l
tirely free from noise; are easily
kept clean; are easy to a horse's hoof;
lessen very much the wear and tear
of vehicles; are pleasant to travel-
lers; admit of great speed, and are cheaper in their firs
cost than granite blocks.
To counterbalance these recommendations, they are
slippery and therefore dangerous in wet weather; and are
very perishable, both from wear and from decay. The
slipperiness has been obviated by grooving and striating
their surface, but this lessens their ease of draught and
noiselessness, and increases their cost.* The rapidity of
their wear may be lessened by setting them on a foundation of broken stone, or of concrete, so shaped as to rapidly drain the water from their bottorms; and by covering
their surfaces with a mixture of boiling tar and clean
gravel. Their decay may be prevented by various chemical preservatives, of which the principal are, Kyan's, who
saturates the wood with a solution of bichloride of mercury or corrosive sublimate (one pound to five gallons of
water); Burnett's, who uses'a solution of chloride of zinc.
(one pound to ten gallons of water) absorbed in a vacuum;
Renwick's, with coal tar; and Boucherie's, witli the iipure pyrolignite of iron, absorbed by the vital action of
the sap vessels.
* A description of various forms proposed for wooden pavements may
he found in the N. Y. American Repository, vol. iii.; and in London Mechanics' Magazine, and Repertory of Patent Inventions, passim.