186 THE ELECTRIC TELEGRAPH. 



that of expelling the sap, and that of filling the pores of the 

 wood with the preservative solution. 



In his experiments on the impregnation of timber, Dr. 

 Boucherie has made the important discovery that no con- 

 nection exists laterally between the tubes of a tree, and that 

 by applying, under moderate pressure, a coloured solution to 

 certain tubes at one end of a tree, the same tubes at the other 

 end, and only these, are coloured. In this way, at one end 

 of a felled tree, he applied a coloured solution to certain tubes 

 forming the name " Faraday." The name was transmitted 

 to the other end, and was perfect at every intermediate 

 section. 



When the tree is cut down and trimmed, a solution of 

 sulphate of copper is forced into it from one end to the other 

 by a moderate pressure. The sap and fermenting matter are 

 thus expelled, and their place taken up by the solution. The 

 small cost of the apparatus, ease of manipulating it, and 

 the increased durability which it imparts to the wood treated 

 by it, highly recommend the process. It is necessary, how- 

 ever, to take care that no ungalvanised iron comes in contact 

 with wood so impregnated, otherwise the copper of the 

 preservative solution will be reduced. 



Chloride of zinc is also used in Germany with some suc- 

 cess. The posts are put into wrought-iron cylinders of 4J 

 to 6 feet diameter, and 34 to 60 feet long, closed at one 

 end, and covered at the other with tightly-fitting tops. 

 The cylinders are provided with manometers, safety-valves, 

 &c. ; and connected with air and pressure pumps, and a 

 reservoir of zinc- solution. The wood is prepared by being 

 subjected to a great pressure of steam, which, penetrating 

 into the interior, not only tends to displace the sap from 

 the pores and prepare them for the preservative solution, 

 but also to coagulate the albumen in the sap, and in this way 

 to retard the subsequent rotting. After this the cylinders 

 are exhausted, and immediately filled with a solution of one 

 part of chloride of zinc and thirty parts of water, which is 

 kept on, under a pressure of eight to ten atmospheres, for 

 about three hours. 



