SAP-STAIN, MOLD, AND DECAY IN GREEN WOOD. 
35 
cool, an amount, approximately equal to the original volume of the 
escaped air, will be forced into the wood. This is a slow process, 
however, and therefore somewhat expensive. 
The rate of evaporation of the liquid, in the case of hot solutions, 
is much greater than in cold solutions ; hence, it becomes necessary to 
take frequent hydrometer readings of the bath and to make the 
proper adjustments in the relative proportions of the solvent and dis- 
solved substances in order to maintain a uniform concentration. 
Dipping may be of some value when applied to stock free from 
fungi. In those cases 
where the fungi are 
already in the tim- 
ber, however, it is 
doubtful whether 
very much good can 
result from chemical 
dips unless the ma- 
terial be subjected 
first to a relatively 
high temperature 
and for a length of 
time sufficient to de- 
stroy these organ- 
isms. 
The salts used in 
the chemical treat- 
ment of lumber are 
likely to vary con- 
siderably in strength 
and purity. It is 
probable that the 
lack of uniformity 
in the results ob- 
tained by different 
investigators when 
employing nominally the same compounds may be traced partly to 
this cause. A few of the preservatives commonly used are de- 
scribed here. 
SODIUM CAKBONATE AND SODIUM BICARBONATE. 
The substances which have been most frequently employed to pre- 
vent sap-stain in lumber are sodium carbonate (commonly in the form 
of soda ash) and sodium bicarbonate (baking soda). Solutions of 
these salts are applied either hot or cold by dipping in an open tank. 
On southern yellow pine, when used in concentrations of 4 to 5 per 
cent sodium carbonate and 5 to 6 per cent sodium bicarbonate, these 
Fig. 16. — Details of the interior of the steam box used in 
the experimental steaming of red-oak and white-oak 
blocks at the Madison laboratory. 
