204 PRESERVATION OF WOOD. 
H. Vohl, of Bonn, recommends the so-called kreosote (coal-tar oil) for the 
preservation of wood. This kreosote consists for the most part of an ethereal 
oil, with which small quantities of true kreosote and carbolic acid (phenylic acid) 
are mixed. Its practical examination is easy, requiring only that the oil should 
be mixed in a graduated cylinder with some ten per cent. of a strong alkaline 
lixivium, well shaken, and then left to settle. The liquid will separate into 
three distinct portions, the lower of which is purely an alkaline lye; the middle, 
which is brown, and of the consistency of sirup, contains the kreosote and 
carbolie acid; and the upper consists of the ethereal oil. As the volume of the 
substances employed is known, the quantity of kreosote and ecarbolie acid is 
easily determined. Since it is in these that the virtue of the impregnating oil 
resides, this criterion seems well adapted for determining the relative value of 
the latter. It has been stated that the coal-tar oil, received as well from Eng- 
land as from Belgium and France, contains a maximum of from eight to ten per 
cent. of kreosote and carbolie acid, whereas the preparation obtained from the 
photogenic manufacture is much richer in these constituents. 
The presence of much ethereal oil in the fluid obstructs the absorption of the 
latter by the wood, and an eligible method for the preparation is to treat the 
kreosote with an alkaline lye, until, without being decomposed, any desirable 
quantity of water may be mixed with it; a certain proportion of the oil is sepa- 
rated, which is to be decanted from the mixture. The alkaline solution of kre- 
osote, which, after the dilution, has a specific weight of 1.05 in relation to water, 
is applied by spreading it on the wood. When this application is absorbed, 
which soon takes place, the operation is repeated until the wood is sufficiently 
impregnated. Were the wood thus prepared exposed to the weather, a great 
part of the kreosote would be washed away ; hence Vohl employs, for the fixa- 
tion of the kreosote, a weak solution of the sulphate of iron, (iron-vitriol.) The 
sulphate of the vitriol neutralizes the alkaline menstruum of the kreosote, and 
this, now become free, attaches itself to the substance of the woody fibre. The 
precipitated oxide of iron, which entered together with the kreosote, is» con- 
verted gradually into a hydrate of iron, at the expense of the atmospheric oxy- 
gen contained in the wood. The sulphate of soda (glauber salts) formed there- 
with is removed by degrees through the atmospheric moisture. Wood prepared in 
this manner, though exposed to every atmospheric alternation, exhibited, at the 
end of cight years, no trace of deterioration from decay or fungous formations. 
Kreosote has been found of great advantage in the preservation of the rigging 
and sails of ships, not only supplying the place of tar, but excelling it in its 
beneficial effects. The efficacy of this operation rests on the facility with 
which kreosote combines with organic substances treated with lime, such as 
skins, leather, &c.; and in view of this the sails and ropes are first passed 
through a weak solution of lime and then through a strong tan-bath. The lime 
is precipitated through the operation of the tannic acid on the vegetable fibre, 
which thus impregnated readily absorbs the kreosote. Vohl observed no rot- 
tenness in sails thus prepared, after six years’ exposure to all kinds of weather. 
In order to promote the duration of timber used in the construction of bridges, 
it has been proposed to protect those parts exposed to moisture and the atmo- 
sphere with roofing-felt. : 
Rottier, professor of chemistry in the University of Ghent, has recently made 
many experiments, with a view to discover which it is, among the various con- 
stituents of the coal-oil tar, that operates most efficaciously for the protection of 
wood from decay. His examination extended to the light or ethereal oil, the 
earbolic or phenylic acid, the aniline, the naphthaline, the insoluble residuum 
of the distillation, and the green, fluorescent oil which, redistilled at 275° to 
320°, yields pyrene and paranaphthaline. 
Of these elements, the light oil and the aniline evinced little or no efficacy. 
Wood saturated with the first lasted no longer than the same kind without it, 
