852 



Preservation of timber. 



[JAN. 



In these experiments a penetration of from J in. to J in. 

 was obtained in seasoned timber. With regard to chestnut, 

 it is stated that in some cases failure of treatment was due 

 to the tendency of the thin sapwood to scale off after exposure 

 to weather, and that better results might have been secured if 

 the sapwood had been shaved off for a few feet above and 

 below the ground-line, so that the preservative would be 

 applied to the more firm heartwood. Applications of carbo- 

 lineum, creolin and tar were also made with a brush, the 

 absorption of tar by 6 ft. of pole being on an average about 

 7 lb. Care should be taken in this method to fill all splits 

 formed during seasoning; the preservative should not be 

 applied when the surface of the wood is wet or when very 

 cold. In most cases better results will be obtained by heating 

 the preservative before applying. 



Treatment by Immersion. — Immersion in a tank filled with 

 preservative has the advantage, in common with the brush 

 method of application, that the butt end only of poles can 

 be treated, and the expense is avoided of apolying the pre- 

 servative to the portion above ground, which in many cases 

 is sufficiently durable without treatment. The treatment con- 

 sists in subjecting the timber to successive baths of hot and 

 cold preservatives, these latter being thus driven into the 

 wood by atmospheric pressure. Three methods of procedure 

 are possible : — (i) After the timber has been held in the hot 

 preservative for the required length of time, the heating may 

 cease, and without other change the whole be allowed to cool ; 

 (2) the timber may be transferred from the hot liquid to 

 another tank containing cooler preservative ; and (3) the pre- 

 servative may be changed, the hot being drawn off and colder 

 preservative run into the treating tank. The hot bath, as a 

 rule, simply prepares the wood for treatment, absorption 

 taking place, except in the case of very dry and porous woods, 

 during cooling. 



The length of time during which the wood must be kept 

 under treatment is dependent among other things on the 

 species and condition of the wood. Thus where the sapwood 

 is narrow and the heartwood difficult of penetration, the treat- 

 ment should be discontinued after the sapwood has been 

 impregnated ; and where the sapwood is wide, the period of 



