SEASONING AND IMPREGNATION OP TIMBER 277 



It is doubtless true that this and other salts exert a 

 retarding effect on the fungus threads, some more than 

 others ; the main objection is that the salts are soluble and 

 liable in time to be washed out of the wood. 



The Wellhouse or Zinc Tannin Process has been a good deal 

 used in the United States and is an effort to overcome the 

 above difficulty by injecting into the timber, in addition to 

 the zinc, a solution of glue and tannin, either in one opera- 

 tion or separately ; the latter appears most satisfactory, but 

 is more costly. It is claimed that the glue and tannin form 

 small particles like leather, insoluble in water, which plug 

 up the ducts and retain the zinc chloride. 1 The Germans 

 as well as the Americans are experimenting on a large 

 scale with a combination of zinc and creosote ; a large 

 proportion of the ties or sleepers on the Prussian rail- 

 ways are treated by this process. But the difficulty with 

 all mixtures of zinc and tar oil is that if the mixture is 

 injected at one operation a poor tar emulsion is likely 

 to result, whilst if each is injected separately it is expen- 

 sive. In some cases it was found that the pieces of wood 

 at the bottom of the cylinder received large quantities 

 of oil whilst those at the top received but a very small 

 quantity. 



Burnettizing, either in its simplest form or combined 

 with other materials as described, is the system of pre- 

 servation most generally used for sleepers on the United 

 States railways and is recommended, not because it is con- 

 sidered the best system, but because of its cheapness, yet 

 even amongst American railway engineers there is great 



1 At a recent meeting of the Wood Preservers' Association of 

 America it was stated that the amount of timber treated by the zinc, 

 glue, and tannin process in 190(5 had very much decreased compared 

 with the quantity treated in 190o. 



