SEASONING AND IMPEEGNATION OF TIMBEE 277 
It is doubtless true that this and other salts exert a 
retarding effect on tlie 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.^ Tlie 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 mixtum 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 1906 had very much decreased compared 
with the quantity treated in 1905. 
