THE PRESERVATION OF WOOD FROM DECAY. 83 
around them, and the tank filled with the solution to be used. Sometimes the 
tree, immediately after felling, was placed upright, with its lower end in a vat of 
liquid. In either case the preservative solution was drawn upward by the capil- 
lary force of the tree, and penetrated even to the leaves. According to Hyett ^ 
a poplar tree, ninety feet high, placed thus with its lower end in a solution of 
crude acetate (pyrolignite) of iron of sp. gr. 1.056, absorbed about ten cubic feet 
of the solution in six days. In a variation of this method, the preservative was 
appHed to the top of the recently cut log. being enclosed in a kind of rubber cup. 
Different sorts of wood were then found to be differently penetrated. Beech 
absorbed the antiseptic readily, poplar with less ease, and ash scarcely at all. 
Heart-wood of Scotch fir, says Hyett, resisted permeation entirely. But all these 
methods of impregnation have been supplanted by the process which originated 
with Breant, and which, adopted since by Bethell, Burnett, and Boucherie, has 
been made well-nigh perfect. The wood to be preserved is enclosed in a strong 
iron cylinder, from which the air is exhausted by means of a powerful steam 
pump. Then, under great pressure, the antiseptic fluid is allowed to flow in 
and permeates the wood in a most complete manner. Of course, the cylinders 
vary in size, and different pressures are employed. The most convenient dimen- 
sions seem to be about thirty-five feet by five, and the suitable pressure, about 
125 pounds to the square inch. 
As for the antiseptics which have been applied by these various methods to 
the preservation of wood, the list is very long, beginning with the recommenda- 
tion of tar by Glauber, in 1657. Coal-tar, vegetable tar, creosote, petroleum 
bitumen, and the so-called "pyrolignite of iron," have all been employed. Rosin 
has been used for the protection of wooden pavements in Cleveland. Solutions 
of rubber in naphtha or bisulphide of carbon have been recommended, but are 
of course too costly. Munzing, in 1840, suggested the use of the refuse liquor 
of the chlorine manufacture. Tannin, extracted from peat moss, gave unsatis- 
factory results. An arsenical solution, obtained from arsenical pyrites, was found 
to be dangerous to the workmen. Lime, and the alkalies, according to Parnell 
really hasten the decay of wood; lime, however, has been highly recommended 
by some writers, and possibly it may work very differently with different varieties 
of wood. The other agents which have been proposed as preservatives, are com- 
mon salt, sodium sulphate, borax, saltpetre, potassium dichromate, sugar of lead 
zinc chloride, zinc sulphate, verdigris, copper nitrate, copper sulphate, ferric 
nitrate, ferrous sulphate, corrosive sublimate, and the various agents used in the 
process commonly known as " creosoting." This Hst may not be quite complete,, 
but it is nearly so. Some of these compounds have been found ineffective, and 
others, as for instance borax, '^ have not been sufficiently tested. 
The value of salt as an antiseptic is well known, but needs farther testing 
with reference to the preservation of wood. For this purpose it seems first ta 
6 See Parnell's Applied Chemistry. 
7 Recommended by Sigismund Beer. 8ci. Amer. "Vol. 18. 
VII-6 
