198 PRESERVATION OF WOOD. 
water. Of this fact ocular proof may be had, if, by means of strong hy- 
draulic pressure, we drive the albuminous substances from a stick of wood and 
prepare it after the prescribed manner. The vitriolic solution which is received 
at the end of the wood, where it flows out, possesses the same properties as atits 
introduction; there has been, therefore, little or no intermediate action. For 
every sort of wood there is a certain degree of pressure under which the prep- 
aration yields the best results. Nor is the strength of the vitriolic solution of 
~ Jess consequence than the force of the pressure: too weak, the effects are cor- 
respondent, unless much time is allowed for the preparation; by to> great con- 
centration, on the other hand, we injure the absorbing vessels of the cellular 
tissue, and the preparation becomes difficult, if not impossible ; the wood in this 
case may be said to be scorched and corroded by the acids. The proportion 
recommended is a solution of one pound of the sulphate of copper in one hun- 
dred pounds of water. The water to be used for this purpose must be pure 
and as free as possible from calcareous salts. 
All kinds of wood are not suitable for this impregnation. Certain kinds 
have isolated parts, where the sap is arrested, and no passage is allowed for 
the solution. In the oak, for example, the sap only is penetrable, while the 
pith resists penetration. The beech even, which is highly adapted to impreg- 
nation, often shows, near the pith, a red portion, in which the sap becomes in- 
spissated and allows no passage. The birch and yoke elm admit of easy and 
thorough preparation, provided the age of the former be not more than forty 
nor that of the latter more than one hundred years. The pine, the linden, the 
plane, the service tree, the elm, and the aspen are well adapted to this purpose. 
In all trees the sap is the part most susceptible of impregnation, and this part, 
which is usually considered as unserviceable in constructions, the process of 
Dr. Boucherie renders fit for employment. The same is the case with many 
kinds of wood which grow in wet grounds, whose affluence in albuminous sub- 
stances would, without such preparation, subject them to rapid decay. 
For the success of the proposed method, it is indispensable that the juices of 
the tree should possess their full degree of fluidity, so as to yield readily to the 
pressure by which the preservative liquid is introduced. From the 1st of Sep- 
tember, in many countries, but in general from the 15th of that month onward, 
the vegetable activity diminishes, the leaf changes color and soon falls. * At 
this period the sap becomes thinner, circulates with more facility, and yields so 
much the more readily to the antiseptic liquid. Trees felled in September, 
October, and November may await preparation for a longer time, in proportion 
as they were later cut. ‘he more advanced the season, the less is the tendency 
of the sap to coagulate and obstruct the vessels of the cellular tissue. In trees 
felled in October this condition scarcely supervenes before the end of November, 
while in those severed in January, February, and March, provided the boughs 
be left entire, the fluidity of the sap continues till the end of May. In general 
the sap of standing trees attains its highest degree of tenacity from the middle 
of April to the beginning of June; trees felled at this season, which is the most 
unfavorable, admit only of difficult and imperfect preparation. During the 
following months of June, July, and August the process should be applied 
within eight days from the felling of the tree, else the dryness, which promotes 
coagulation in the still otherwise tenacious sap, will tend to embarrass the upe- 
ration and in some cases render it very impertect. As a general rule it may be 
assumed that the most favorable epoch for the impregnation of wood is that in 
which the felling is generally considered as advantageous. 
At whatever time the impregnation may be undertaken, it is always of great 
importance to select the soundest and straightest timber, and such generally as 
had not begun to decay and is free from clefts. The antiseptic liquid, on its 
introduction into the wood, will take the course where it meets with least 
obstruction, and if faults like those mentioned exist, will find through the 
yielding or divided parts a channel of escape. 
