Wood′en Pave′ment.
See pavement, pages 1639-1642, and Plate XXXVIII. The experience of American cities which have used woodpavement goes to show that some system of preservation is necessary to secure a durable wood-pavement. If the question of wood-preservation is not finally and perfectly solved, it must be admitted that the methods now in use show a decided progress in that direction. The respective efforts tend to neutralize the external influences of water, air, and heat, by. First. A more or less complete removal of the water and extraction of the aqueous solutions of vegetable matters contained in and between the cells and fibers of the wood. This is done mostly by pneumatic process, in iron air-tight cylinders. Second. A subsequent injection of fluids under hydrostatic pressure, by means of which permanent chemical combinations are formed. These antiseptic fluids are either diluted metallic solutions (impregnation proper) or those oily substances obtained from the distillation of tars. The oils, which are obtained at certain temperatures of distillation (varying from 180° to 230° Fah.), are charged with substances (also the product of the distillation) which coagulate all albuminous matter, rendering it insoluble, and in some degree, fixed. This action penetrates even the cells where this albuminous matter is mostly found. Besides the chemical action of this kind of treatment, it also acts mechanically by repelling water, or at least reducing absorption measurably; and in the Robbins process, if thoroughly carried out, the pores become more or less closed with resinous matters. The following processes have been used, namely:—1. First class, or impregnation with metallic solutions.
（a.) Burnettizing, or impregnation of chloride of zinc.
（b.) Samuels's process of impregnation with sulphate of iron.
2. Second class, or injection of oily substances.
（a.) The Seeley process; impregnation with creosote, carbolic acid derived from pine tar.
（b.) Robbins's process: impregnation with heavy oils charged with creosote, carbolic acid, etc., derived from coal-tar at a higher temperature than by the Seeley process. Where ironizing has been tried, reports from various cities are unfavorable. This stands to reason, since sulphate of iron is well known to have no affinity for the formation of insoluble combinations with the vegetable matters to be neutralized, nor has it hardly any poisonous action on low organisms when applied in diluted solutions. The disengagement of sulphuric acid, in consequence of oxide of iron being fixed upon the fibers, also tends to exercise a destructive influence on the texture of the wood, being so much stronger than the hydrochloric acid that may be liberated by the Burnettizing process, The function of the acids being that of merely conveying metallic oxide, of course the use of the weaker acid is preferable. Creosoted wood has, in some cases, proved offensive. It has to be handled with great care by the workmen, as it produces eruptions and sores, and in Belgium its use for preserving telegraph-poles was abandoned on account of this; otherwise it is efficient and lasting. See wood, preservation of.
