The oil also prevents glue from sticking, the most frequent cause of injury to handscrews.
(6) There are a number of "impregnation" methods of preserving timber, and their practice is spreading rapidly.

Of the various preservative processes, those using coal tar creosote and zinc chloride have proved most efficient.

The purpose is to force the preservative into the pores of the wood, either by painting, soaking, or putting under pressure.

Such impregnation methods double or treble the life of railway ties.

It is now being used with great success to preserve electric wire poles, mine-props, piling, fence-posts, etc.
Wood preservation has three great advantages, it prolongs the life of timbers in use, reduces their cost, and makes possible the use of species that once were considered worthless.