200 PRESERVATION OF WOOD. 
wood and obstruct unnecessarily some of the tubes destined to convey the anti- 
septic fluid. . : ‘ 
The screw by which the middle of the log was raised being now withdrawn, 
the log of course sinks, the two side walls of the incision approach, pressing 
together the included cordage, the circuit of the opening is completely closed, 
and thus an artificial reservoir is formed in the midst of the piece which is to 
be impregnated. 
Into the hole, bored as above directed, a tube of hard wood is driven, and is 
fastened to one of India-rubber which has been previously adjusted to the cop- 
per taps of the leaden pipe, thus establishing a communication between the 
small reservoir in the middle of the log and the distributing apparatus. During 
the preliminary steps, the India-rubber tube is closely compressed by means of 
a hand-serew, but when, at the commencement of the process, this is removed, 
the impregnating fluid flows into the reservoir prepared for it in the log, and 
‘drives the sap before it through the pressure exerted by the fluid in the vessel 
which feeds the supply tube. Under favorable circumstances this effect is 
instantaneously manifested by an exudation at the end of the log, which pres- 
ently changes into drops, and falls into the channel provided for it. ‘To remove 
any included air which might interfere with the process, a small hole should be 
made with a copper pin through the cord enveloping the incision, which must 
be closed with the stroke of a hammer as soon as the fluid begins to issue. It 
will also greatly promote success, if in the course of the operation the incision 
be occasionally well cleansed, and again closed with the same care as at first. 
The sap, which at first issues pure, becomes more and more mixed with the 
vitriolic solution as the process approaches its termination. When this mix- 
ture shows 3° (its normal strength being 1°) the penetration of the wood may 
be regarded as complete, and for pieces of the length of a railroad sill, the time 
in which this result is reached may vary from 48 to 100 hours; all pieces 
which, after the lapse of the latter period, do not exhibit in the centre of the 
end-surface a readily distinguishable impregnation, must be turned, and the 
operation conducted in the opposite direction. 
For the preparation of longer pieces, such as telegraph poles, building ma- 
terials, &c., in which the difficulties are greater, it will be useful to observe the 
following precautions: 1. To place the vessel which contains the solution 
higher, in order to increase the pressure. 2. ‘To cleanse the imbibing surfaces 
oftener, with a view to remove impurities which may gather upon them. 3. To 
elutriate the fluid more frequently. 
The arrangements for operating are like those above described, with the ex- 
ception that here but two beams, laid parallel to one another at a distance cor- 
responding to the length of the pieces, and with an inclination of 1 to 8, are 
required; the introduction of the solution will take place only at that end 
which shall give it the same direction with the natural sap; the artificial res- 
ervior ,constructed and closed as before described, will be near the but-end of the 
log, and the surface of the incision next to this extremity should be covered 
with a sheet of copper to prevent the penetration and escape of the impregna- 
ting fluid through the shorter section, 
The acceleration of the process depends on the kind of wood, the season at 
which it is cut, and the effective pressure employed. Apart from these, the 
rapidity of impregnation may be assumed as proportional directly to the pres- 
sure and inversely to the diameter and the square of the length. Moist winds 
and snow hasten the process; dry winds and great aridity retard it; frost alto- 
gether arrests it. 
This mode of preparation has been tried and approved by a number of the 
railroad and telegraph administrations of France. In 1856 more than 400,000 
cross-ties thus prepared had been laid on the North road, 8,000 of the number 
having been deposited as early as 1846. In the former year these latter were 
