90 TIMBER AND TIMBER TREES. [CHAP. vil. 



Steam, saturated with the preservative, is forcibly driven 

 in. The chief advantages clainaed for this process are (i) 

 that unseasoned wood can be effectively treated, (2) the 

 antiseptic liquid is driven in to a greater depth than by 

 any other method, and (3) the process is very rapid, it 

 being possible to impregnate many tons of timber in less 

 than an hour in large cylinders. 



A very ingenious method, invented by Boucherie, has 

 been employed in France. This consists in attaching a 

 pipe to the lower part of a log, so that the antiseptic 

 solution employed, under a pressure of about one 

 atmosphere, is gradually forced in to displace the natural 

 fluids of the sap-wood of the tree. The pressure is 

 obtained by elevating the reservoir of antiseptic. Sulphate 

 of copper and chloride of zinc have been thus used, but 

 since the log must be treated with the bark on (other- 

 wise there is great loss at the surface) there are many 

 drawbacks to this method — e.g. loss in conversion and 

 carriage — except where whole trunks are employed and 

 directly treated on the spot. 



