PRESERVATION OF WOOD : 201 
found to be as sound as they were the day they were laid, and this remarkable 
preservation, which they still manifest, leaves no room to conjecture the possible 
extent of their duration. 
Expensive apparatus has been sometimes employed for the purpose in ques- 
tion; as, for instance, an air-pump, operated by a steam-engine, to exhaust the 
air from the wood, and thus facilitate the penetration of the metallic solution. 
Powerful hydraulic presses have also been used to promote this result. Such 
costly contrivances, however, may be wholly dispensed with. Biittner and 
Wohring, of Dresden, among others, have proposed a process which is at once 
practical and cheap, and which quickly attains the desired end; their method 
has been consequently introduced in the case of several Saxon, Austrian, and 
other roads. 
This method consists, as regards its chief feature, in the exhaustion of the air 
from the vessels of the wood—a condition indispensable to arapid and thorough 
impregnation, not by mechanical forces, but exclusively by those of temper- 
ature. The whole operation is, in fact, conducted on this principle, the wooden 
sills being boiled for the space of an hour in a solution of metallic salts, and 
then left to cool undisturbed in the same until the temperature has sunk to 40° 
R. The physico-chemical process is here as follows: Through the heating of 
the wood to more than 100°, not only are the included gases but also the ex- 
tractive substances expelled, the escape of the former being made manifest, 
throughout the operation, by the rising of large air bubbles, and the separation 
of the latter by a viscous substance floating on the surface of the solution and 
indicating even by its scent its vegetable origin. The wood, as it cools, being 
surrounded by the solution, rapidly absorbs it to supply the vacuity occasioned 
by the expulsion of air—an effect which is aided by the pressure of the atmo. 
sphere on the liquid surface exposed to it. 
That the hot way for the impregnation of wood is decidedly preferable to 
any cold method of preservation would seem to result from the law that all 
organic chemical combinations are more certainly obtained in that way; be- 
sides that the contingency of protracted rains, which, in the cold process, some- 
times wash away the metallic salts, is thereby avoided. At the same time, 
through the heat and vapor pervading the wood, a coagulation of the albumen 
may be occasioned, which probably, even without the intervention of the metal- 
lic salt, would of itself impart a preservative quality to the wood; for, as has 
been already said, the decomposition is to be solely ascribed to the ingredients 
of the vegetable sap, while the vegetable fibre in its simple state not only 
withstands the influence of the weather, but remains impassive under the sharpest 
reagents. 
After persistent boiling for an hour and a half the heat will be found to have 
thoroughly penetrated the sill, and the highest rarefaction of the included air to 
have been attained; consequently the capacity of absorption will have also 
reached its highest point, which is estimated at 14 cubic foot = 62 pounds of the 
solution for a piece of wood of 2 cubic foot contents. It has been determined 
by many experiments that this is to be regarded as the maximum of absorption, 
which will not be increased even if the boiling be continued for several hours. 
Asacubic foot, = 50 pounds of the solution, is sufficient, therefore, for the preser- 
vation of a sill of pine wood, and its absorption is effected in one hour’s boiling 
and from six to seven hours’ cooling, it is apparent that the same apparatus may 
be twice used within twenty-four hours for the proposed operation. : 
The apparatus in use on the government railroad of Saxony consists, in the 
main, of a boiler of 10 horse-power, exerting a tension of two atmospheres, 
with a provision of four pine-wood receptacles, each 114 feet high and 8 wide, 
for every boiler of the above description. The steam is conducted through an 
inch-wide tube from the boiler to the bottom of the receptacle, and traverses 
the latter through a tube of like width provided with small holes. The pieces 
