106 



not mechanically, a creosoted pile is an unhoniogeneous structure, the unimpregnated 

 interior being intrinsically no more immune from borer attack than any other un- 

 treated wood, and dependent for its protection on the maintenance of the complete 

 integrity of the zone of J;2 to IJ-o inch thickness of creosote impregnated wood with 

 which it is surrounded. Insofar as the rupture of this zone is easier than would be 

 ideally desirabieand as the accepted methods of working with wood provide the tempta- 

 tion to cut and frame and use dogs and pike poles on construction such as this, to 

 its grave injury, creosoted piling may be called a fragile protection and should be 

 treated as should any construction material, with special and intelligent regard to 

 the safeguarding of its particular weak points. 



While creosoted piling has been in use continuously for many years, it has not 

 been generally adopted until recently for several reasons: the process is expensive, 

 and the demand for this type of creosoted product has not been large enough that 

 commercial treating plants could be maintained on the local consumption, or could 

 compete in the general field with plants at the source of production of the timber 

 chiefly used for construction purposes. As a result, San Francisco Bay has only one 

 treating plant and that is owned and operated by a railroad ior its own requirements 

 only. The difficulty of procuring the piling from distant plants has sometimes led 

 to substitution of other types; sometimes improper treatment and often improper 

 handling have curtailed the effecti\'eness fif the protection and shortened its life, thus 

 causing confidence in it to be lessened. As time has progressed, however, the causes of 

 premature failure have been disclosed, and the consistently good ser\'ice of piles 

 properly treated and handled has firmh' demonstrated the high \alue of the process. 



Treatment of Dougl.\s Fir Piling 



Douglas fir is very refractory to the penetration of preser^•atives in the heartwood. 

 The sapwood is less refractory, but it is difficult to obtain an absorption in Douglas 

 fir piling of much over 12 to 14 pounds per cu. ft. of treated material. The thickness of 

 the sapwood is the ultimately limiting factor in the depth of the penetration that 

 can be secured. 



The piles driven in Oakland Long Wharf in 1890 and 1892, totaling about 1000, 

 were air-dried for a year before treatment, then treated by the Bethel process, absorb- 

 ing about 14.2 lbs. per cu. ft. The other 13,000 piles in this structure were treated 

 green from the water, by the boiling process as de\'eloped by John D. Isaacs, and 

 received an average absorption of about 10 pounds per cu. ft. Since that time piles 

 have been used in the bay treated by the steaming process, the boiling process and the 

 boiling under vacuum process. All three processes are still used but the present 

 tendency seems to fa\'or that of boiling under vacuum. (See specifications for creo- 

 soted piling and timber for use in marine structures, beginning on page 108.) 



The Spliced Creosote-Greenwood Pile 



Some creosoted piling has been used in San Francisco Bay, to the small or bottom 

 end of which is spliced an untreated piece somewhat shorter than the length which will 

 be driven below the mud line. This device permits the purchase of much shorter 

 creosoted piling, which is also cheaper per linear foot than material of longer and 

 larger dimensions. It may give satisfactory service, if the splice is sufficiently strong, 

 subject to precautions against the exposure of untreated wood by miscalculation of 

 driving length, or by subsequent scouring of the bottom. The late Mr. Howard 

 Holmes, of San Francisco, used successfully a metal sleeve of several feet length 



