77 
to the woody liber, which prevents water and air from coming in contact 
with it. B6ing insoluble in water, it cannot be removed by immersion 
in water. It is, moreover, the only substance which will permanently 
protect timber against destruction bv the Teredo ndvdtts and other 
r Jiarroa vTI'v>ri')<r *y<loJ jmtjioi o*row f «>nn.J otnf.t 
parasites. 
Impregnation with heavy oil of tar, or crepsbting, as it is sometimes 
called (from the tact that creosote was considered the active .preserva- 
tive principle), was patented in England by Uethell, in 1838. 
The method of treatment proposed by him was to remove the air from 
the wood, to heat the oil to about 120° Fahr., and to inject it iuto the 
wood by pressure. To admit of proper impregnation, the wood should 
be freed from water so far as possible. In England, air-dried wood is 
readily procured, which being placed in a closed vessel in which a vac- 
uum has been established, can be easily prepared for the reception of 
the oil. In this country, where the wood generally has to be impreg- 
nated soou after it has been cut, and wheu steaming has to be resorted 
to for driving out the sap, special means must be adopted to remove 
the water of condensation from the wood, after steaming, if the treat- 
ment is to be successful. 
As to the quantity of oil required to preserve the wood, it may be 
said that the useful effect of the impregnation is proportional to the 
quantity of oil injected into a given volume of wood. If all the void 
spaces in the wood could be filled, it would take from one-half to two- 
thirds of a cubic foot, or from 35 pounds to 50 pounds of the oil for each 
cubic foot of timber. The practical limit would probably vary from 25 
to 50 pounds per cubic foot, according to the kind of timber used. 
But impregnation to such an extent would be altogether too expen- 
sive, and the quantity is therefore limited to what has proved by ex- 
perience to be adequate for preservation under the conditions in which 
the wood is to be used. From 5 to 7 pounds per cubic foot is at pres- 
ent considered sufficient for railroad ties j about 10 pounds per cubic 
foot for bridge timbers ; and for protecting piles used in marine struct- 
ures, from 18 to 20 pounds per cubic foot are considered necessary ac- 
cording to the experience of American and French engineers, while Eng- 
lish engineers consider 10 pounds per cubic foot sufficient protection 
for timber and piles in marine works. 
The value of creosoting as a preservative against decay is shown by 
long experience. Iu England it is almost universally used for preserv- 
ing railroad ties. Creosoted ties have been found perfectly sound after 
they had been in the ground for twenty- two years. In this country, 
creosoting was first applied in 1865 by Hinckley, on the Old Colony 
Railroad, for the preservation of piles ; but the treatment was very im- 
perfect, as the oil did not penetrate to a depth of more than one-quarter 
to one-half an iuch below the surface. The piles were also trimmed and 
cut after treatment, thereby exposing untreated surfaces. 
