34 



BULLETIN 1037, U. S. DEPARTMENT OF AGEICULTUEE. 



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- 



FlG. 



15. — steam box of cypress used in the experimeEtal 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 j)ene- 

 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 



