MATERIALS USED EOR INJECTIOX. 66 i 



2. Materials used for Injection. 



A number of substances have for a long time been known 

 which rendev wood durable, such as resin, essential oils, 

 camphor, tannic acid, acetic acid, heavy tar-oil (creosote) ; also 

 several salts, as green, white and blue vitriol (sulphates of iron, 

 zinc, and copper), chlorides of iron, zinc, mercury or magnesia, 

 Glauber's salt (sodium sulphate), common salt, &c. Onl}' a few 

 of them are, however, applicable on a large scale and of these 

 the following are at present in the front rank : — sulphate of 

 copper, chlorides of zinc or mercury, heavy tar-oils (creosote) and 

 milk of lime. There are also a few other substances the use of 

 which is still only in the experimental stage. 



Injection with sulphate of copper (blue vitriol) was first 

 em])loyed in France on a large scale by Boucherie, and has been 

 extensively used for the last sixt}^ yeavs for building-timber, rail- 

 way-sleepers and telegraph-poles. This method was at one 

 time extensively used by railway companies in France, Austria, 

 and Bavaria ; this is no longer the case, though it is still 

 here and there employed for telegraph-poles, stakes and other 

 small pieces of timber exposed to decay. Wood injected with 

 sulphate of copper is harder than wood in its natural condition, 

 but is rendered more brittle and weaker by the process. 



[The salt is also easily washed out of the wood and it reacts on all 

 iron with which it may come in contact, so that iron-fastenings 

 applied to wood so treated must be galvanised, or coated with zinc 

 and the wood tarred at the points of contact. — Tr.] 



Sir W. Burnett, in 1838, patented a process of injection by 

 means of chloride of zinc, which is at present used in many 

 German, Austrian and American railways. Chloride of zinc is 

 one of the cheapest antiseptic substances and recent experience 

 has proved that it is preferable to sulphate of copper. 



[Chloride of zinc does not corrode iron but is said to be washed out 

 by water ; to prevent this the Wellhouse * process has been invented 

 in America. Glue is added to the solution, which is forced into the 

 timber, and subsequently a solution of tannin is pumped into the 

 injecting chamber, at a pressure of lOOlbs. to the square inch, 



* Engineer, Sept. 11, 1891. 



