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 CARBONATE 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. 



