Connecticut western news., 1908-05-07
SOME METHODS OF
 PRESERVING WOOD
CRE0S0TE AND ZINC CHLORID
How the PreserVatives May be Applied -Creosote Tends to Conserve the Strength of the Wood.
Continued from last week.

UT the many antlSeptlcS which have been proposed for the preservation of timber only four have been largely used with success in the United States. These are creosote, zinc chlorid, corrosive sublimate (bichlorid of mercury,) and copper sulphate. At the present time copper sulphate has fallen into almost total disuse, and corrosive sublimate Is restricted to two plants in New England. The use of this latter is the so-called "kyanizing" process which is so ire quently referred to in all the literature of wood preservation. In general, the process consists ill sleeping the timber in dilute solution of corrosive sublimate long enough to insure thorough pene- tration.
 Thus in the United States creosote and zinc chlorid are the only preserva- tives in common use. There are many other patented substances known by va nous names; but most of them have for preservatives. CTeosote is a by-product of coal tar, which is produced at most plants for the manufacture of illuminat- ing gas and at by-product coke-oven plants. This tar is distilled, and during the process the condensed vapors are run into three separate vessels and thus separated into the light oils of coal tar or creosote, and pitch Creosote is not a simple substance like zinc chlorid. On the contrary, it contains large number of constituents of great chemical complexity.
 Wood tar, when distilled in similar manner, gives wood creosote.'' which like that derived from coal tar, possesses strong antiseptic properties. There i~ also on the market so-calleG creosote, by-product of water-gas tar or tar man- ufactured from kerosene oils, which for wood preservation is probably in- ferior to the true creosote. In general, however by "creosote' is meant the dead oil of coal tar.
 Zinc chlorid is obtained by dissolvipg metallic zince in hydrochlotic acid. This Is further diluted by water before it is used for wood preservation.
 In the injection of the preservative by the open-tank process, the wood is first thoroughly seasoned, and much of the moisture in the cells and intercellular spaces is replaced by air. If the timber is peeled soon after cutting. and stacked in open piles, the time required for seasoning can be greatly lessened. The seasoned timber, or that portion of it which is to be preserved, is immersed in hot bath of the preservative contained in an open iron tank. This hot bath IS continued for from one to five or six hours, depending upon the timber. During this portion of the treatment the air and moisture in the wood expand and portion of them pass ont, appear ing as little bubbles on the surface of the fluid. At the end of the hot bath, as quick a change as possible is made from the hot to cold preservative This causes a contraction of the air and moisture remaining in the wood, and, since portion of it had been expelled, a partial vacuum is created which can be destroy ed only by the entrance of the preservative. Thus atmospheric pres sure is needed in most of the com mercial plants. Whether the open-tank or pressure-cylinder method is the more desirable depends upon the particular conditions of each case. Both methods have their particular uses and neither can always be wholly substituted for tl.e other.
 A less efficient but cheaper treatment can be secured by painting the surface of the timber with at least two coats of hot creosote or some similar preserva- tive. The liquid may be applied with an ordinary paint brush, but care should be taken to fill thoroughly with the preservative all checks, knot holes, and similar defects. The liquid can pene- trate only very short distance into the wood, but as long as there remains an unbroken antiseptic zone around the surface, the spores of the wood destroy ing fungi can not enter. It is especially important In this method that the timber should be thoroughly air-dry be- fore treatment. Otherwise the evapo- ration of water from the interior of the 1 stick will cause checks to open up and 80 expose the unprotected wood to fungous attack.