14 
On the Preservation of Timber. 
d'c. In" salt-mines, pieces of oak and fir have been observed 
covered with salt water, which have been preserved for ages 
without the least alteration. It is also stated that the Americans 
employ it for preserving the outside planking of their ships. 
Of course, in localities where there is an excess of water, the 
salt may be entirely removed, and thus leave the woody tissues 
exposed ; and in localities alternately wet and very dry, sea-salt 
comes to the surface as an efflorescence. 
Chloride of Calcium. — Chloride of calcium acts in the same 
manner, but it offers some other advantages, as, for example, 
where timber is used in dry places it preserves the wood from 
alteration by its hygroscopic property, and enables it to retain its 
elasticity. 
Sulphate of Soda. — Similar remarks apply to the alkaline sul- 
phates and nitrate of potash, but the sulphate of soda has an 
action the very reverse of chloride of calcium, for it possesses the 
property of drying wood with great rapidity. 
All these saline substances can only act by mingling with the 
sap ; and timber, so to speak, thus salted, is evidently protected 
from decay, and Boucherie attributes to the alkaline chlorides a 
preservative action little short of pyrolignate of iron. 
Class XI. Puncturing Timber, Sfc. — The previous processes 
all depend upon the penetration of the preservative material in a 
state of solution, but there is one patent by Kemp, who, in addi- 
tion to the means already noticed, punctures the wood by the 
spike of a puncturing roller, and fills the perforations with a 
solid mixture of arseniate of copper, carbonate of barytes, and 
red lead. 
Class XII. Charring the Surface.— Instead of applying any 
foreign external agent to protect the timber, a patentee, of the 
name of Ferguson, has proposed to convert the outer layers of the 
wood into charcoal, by passing large heated iron rollers over the 
surface. This principle of charring wood has long been in use 
when inserting timber posts and poles in the ground ; but while 
the charred portion resists the action, and to a certain extent pro- 
tects the inner layers, yet after the lapse of some time the external 
coatinff of charcoal alone remains in a sound condition. 
Class XIII. External Coatings. Wax and Fat. — This divi- 
sion of chemical and other agents embraces all those proposals 
which mainly rely for protection on external applications, and 
among which may be noticed all the oils, fats, and resins whose 
preservative action is chiefly mechanical. It is said that a mixture 
of melted wax and fat may be introduced into wood to the extent 
of even 60 per cent., and for certain purposes is most beneficial, 
as it prevents the wood from twisting and cracking. 
