34 BULLETIN 1037, U. S. DEPARTMENT OF AGRICULTURE. 
sapwood of red oak and then dipped for 10 seconds in solutions of 
copper nitrate and copper sulphate at ordinary temperature showed 
that these solutions had penetrated the ends of the blocks for a dis¬ 
tance less than 5 millimeters (one-fifth of an inch) and scarcely a 
measurable amount in the case of the tangential or radial surfaces. 
It is evident, then, that whatever value there is in the use of cold 
dipping solutions lies entirely in the superficial coating of the pre¬ 
servative left upon the wood. Provided this is not brushed off or 
washed off by rain, it may inhibit or prevent the germination of 
fungous spores which happen to fall upon such surfaces. Hot solu- 
Fig. 15.—Steam box of cypress used in the experimental steaming of red-oak and 
white-oak blocks at the Madison laboratory. 
tions, in that they tend to prevent the collection of bubbles of air 
upon the surface of the wood, probably give a more uniform distribu¬ 
tion of the preservative over the dipped material. As far as pene¬ 
tration is concerned, however, it is doubtful whether the hot solu¬ 
tions, as ordinarily employed, possess any very great advantages. A 
slightly increased penetration may be secured by first subjecting the 
stock to a thorough steaming or by heating it for some time in a hot 
solution of the preservatives, as in the open-tank process. The air 
within the cavities of the wood is thereby expanded, and some es¬ 
capes. Provided the steamed or hot wood is at once transferred to 
a cold solution of the preservative and there allowed to remain till 
