164 



In commercial treating practice varying impregnations often result trom sub- 

 stantially uniform treating procedure, due to differences in the penetrability of different 

 wood species or specimens used, or to varying ^-iscosities of different oils or fractions. 

 This is, however, largely a function of the time factor, as well as of temperature and 

 pressure, and can be practically overcome, as it was in our experimental work, when- 

 ever minimum treating time is not a requisite. On account of the small size of the 

 test pieces there was practically no core of untreated wood. The amount of creosote 

 remaining in all the test pieces was about 15 pounds per cubic foot, except in the case 

 of impregnation with fraction D (see table 14). Here some difficulty was experienced, 

 but a reasonably satisfactory treatment was finally secured, which was approximately 

 10 pounds per cubic foot. 



After treatment the pieces were made up into gates, each holding eight pieces, 

 corresponding to eight different treatments. An untreated bait piece was then attached 

 to each treated piece. Since there were 16 treatments, two such gates constitute a 

 complete series. One complete series of treatments was immersed at each of four sta- 

 tions on the Bay: Southern Pacific Oakland Pier, July-August, 1921; San Francisco 

 Pier 7, August, 1921; Crockett, July-August, 1921; Mare Island, September, 1921. 



Five, and in some cases six, pieces were subjected to the same treatment. This 

 gave one piece with each treatment for each of the four stations, and one or two for 

 laboratory use. The 16 treatments were organized according to the following table: 



TABLE 14 



Treatments Used on Test Pieces Exposed in 

 Large Creosoted Gates 



1. Whole creosote oil. 



2. Fraction A (210° C.-235° C). 



3. Fraction B (235° C.-315° C). 



4. Fraction C (315° C.-355° C). 



5. Fraction D (Residue above 355° C). 



6. Fraction D (Repeated). 



7. Whole oil plus fraction A. 



8. Whole oil plus fraction B. 



9. Whole oil plus fraction C. 



10. Whole oil plus fraction D. 



11. Whole oil minus fraction A. 



12. Whole oil minus fraction B. 



13. Whole oil minus fraction C. 



14. Whole oil minus fraction D. 



15. Whole oil minus tar acids. 



16. Oil tar distillate. 



These oils were synthesized so that the several fractions were added or subtracted in 

 the proportions in which they occurred in the whole oil, which were the following: 



Fraction 210° C.-235° C 10% 



Fraction 235° C.-315° C 40% 



Fraction 315° C.-355° C 23%, 



Residue above 355° C 27%^, 



In view of the difficulties incident to obtaining clear-cut separation by fractional 

 distillation, and consequently to obtaining clearly marked differences in inhibitive 



