PRESERVATION OF WOOD. 205 
and the protraction of decay by the aniline might be expressed as being equal 
only to 6.66 per cent. Phenylic acid is known to be efficacious in the preserva- 
tion of animal substances, and as the heavy tar oil contains it, the virtue of the 
latter was supposed to consist in the amount which it held of the former. But 
Rottier’s experiments do not confirm this conjecture. Coal tar deprived of its 
phenylic acid proved as efficacious as that of commerce, which contains a large 
quantity. Napthaline has proved very effectual in protecting collections pertain- 
ing to natural history from insects; but the presumption arising from this fact 
is not borne out by the experiments of Rottier as regards the preservation of 
wood. It is otherwise, however, with the heavy green oil; this evinced uncom- 
mon efficacy. It remained, therefore, to determine upon which of its constituents 
the virtue depends. Pyrene and paranaphthaline, on direct experiment, yielded 
no favorable results; whence it is to be inferred that it is the green oil itself 
which operates to the protection of wood from decay. It would seem also, from 
the experiments, that the higher the temperature at which the coal tar is distilled 
so much the more operative is it, probably from containing a greater quantity of 
the oil. 
The fact should, however, not be overlooked that the experiments just men- 
tioned have been conducted on a small seale, and the results have not remained 
uncontroverted. More decisive certainly are the experiments made with such 
materials as the sills of railroads, as well on account of the size of the materials 
submitted to trial as the parallelism of the circumstances under which the pro- 
cess is applied. Thus much at least we have already learned, that the preser- 
vation of wood, even to the extent which is now within our reach, is a subject 
which may well excite attention. If we had attained no other result but that 
of being able to impart to soft wood the durability of oak, and hence to substitute 
the eaiee for the latter, this of itself would be of great importance, and be 
attended with many advantages to the various branches of industry in which 
the use of wood is indispensable. 
