0,1 the Preservation of Timber. 
7 
for Duhamel has proved that the smallest pieces of wood do not 
cease to imbibe the liquid after being immersed for six months. 
Class 11. Heated Liquid. — Champy's process is an improve- 
ment on the previous plan, and in some cases might even now be 
advantageously employed, as, for example, in preparing timber 
for fences for railways and agricultural purposes. Champy 
plunges the still humid wood into fat heated to 392°, but any 
liquid of a preservative character, whose boiling point is higher 
than that of water, as oils, resin, tar, &c., may be substituted. 
During the immersion the hygroscopic water is converted into 
vapour and expelled, driving out the air and gas in the tissue. 
On cooling, the atmospheric pressure forces the preservative 
material into the vacuum thus formed in the pores of the wood. 
Light woods, such as pines, firs, poplars, &c.. have been increased 
in weight by this process from 50 to 60 per cent., and have 
proved remarkably sound for years, especially in chemical manu- 
factories, where the acid vapours act more rapidly than ordinary 
atmospheric agents. 
Class III. Gaseous Materials. — Another plan, to which I 
am inclined to attach great value, was first suggested by a 
German, Moll. He exposes wood in a close chamber into which 
he forces steam, rarefying the air, causing the gas contained in 
the pores to escape, and then introduces creosote in the form of 
vapour. Mr. Bethell employs a similar plan in one of his more 
recent patents, and Laing substitutes sulphurous acid gas for the 
creosote vapour. When the difficulty of driving a liquid body 
to the centre of large balks of t:mber is considered, it is obvious 
that great advantage would be gained by substituting a gaseous 
substance. 
It has occurred to me, that by constructing an apparatus which 
could be maintained at a high temperature while filled with 
timber, exhausting the gases by mechanical means, and then 
forcing in the vapour of coal tar in process of distillation, a more 
perfect saturation of the timber would be effected than is even 
accomplished in the ordinary apparatus as improved by Boueherie. 
Class IV. Pressure in Close Vessels. — Monsieur Breant first 
suggested the advantage of employing pressure to force the 
preservative liquid into the pores of wood, and this idea was 
carried into practice by Payne and Bethell. Their plan, and 
that now in common use, consists of a wrought-iron cylinder firmly 
secured to its seat, in a horizontal position, with one end open, 
which can be closed by a lid. The cylinder is fitted with suitable 
arrangements for heating the contents by steam, exhausting 
the products, and then forcing in the preservative liquid by means 
