IMPREGNATION 179 



After impregnation, the liquid is pumped from tlie retort; but the wood is left in it for 2 to 2V2 hours, 

 so as to allow the colophony adhering to the surface of the wood to drop down, and so as to prevent 

 by gradual cooling the formation of cracks. 



By a similar process, heading and staves made of open-grained woods are rendered impermeable 

 to liquids. 



(B) COLOR-IMPREGNATION. At Memphis, Tenn., color-impregnation of various woods is made 

 use of, in a commercial way, under foreign patents. At the Paris World's Fair, in 1900, color-impregnated 

 furniture (notably beech bedroom furniture) attracted attention for the first time. The process is a secret. 



Color-impregnation by ammoniacal fumes is used in all furniture works. 



Professor Wislicenus, of the Tharandt Forest School, Saxony, uses so-called "soil gases" to impart 

 desirable colors without changing or coating the fiber. Pine, beech, birch, larch, oak, and so on, adopt 

 most pleasing shades of color under this process. 



(C) FIREPROOFING. Among the American timber species, the lumber and timber of the sequoias 

 (bigtree and redwood) are known to be most fireproof. 



Impregnation of wood with chemicals similar to those used in the commercial fire extinguishers has 

 been advocated here and there. 



(D) ANTISEPTIC IMPREGNATION intends to bar the activities of timber-destroying bacteria, enzyms, 

 fungi, insects (e. g., white ants), and molluscs (e. g., teredo). Its use has increased, of late years, enorm- 

 ously in the case of railroad ties, telephone poles, and fence posts. Five principles may be applied: — 



I. Immersion: - 



(a) The oldest method used was immersion in a strong solution of ordinary salt (NaCl). 

 Immersion into a 2 to 3 per cent solution of corrosive sublimate is used extensively in the case of 



telephone poles. The poles must be winter- cut, the bark must be removed and the air must be allowed 

 to dry the poles thoroughly, before they are bathed, for 10 to 14 days, in wooden or concrete tanks 

 containing the solution in question. The solution must be stirred from time to time. The chemical test 

 (impregnated wood is blackened by sulphide of ammonia) shows that the liquid enters only into the outer 

 layers of the wood. The method is known as "kyanizing." 



Chloride of zinc, being cheaper, may be used in lieu of chloride of mercury. This substance, however, 

 is more readily leached out by rain. A. Schmidt reports that pine ties had lost, after three years' use, 

 80 to 85 per cent of the chloride of zinc originally injected. 



It is also claimed that the zinc -treated wood fiber decomposes rapidly in close proximity to iron rails 

 or iron spikes driven into wood thus treated because of the influence of free hydrochloric acid. 



In Austria, a 4 per cent solution of acid fluoride of zinc (ZnF_, •2HF) is being used by the governmental 

 telegraph lines for the impregnation of telegraph posts by mere immersion. 



(b) "Metalized" wood is obtained as FOLLOWS:- Immerse the wood in a solution of sulphate of 

 iron ; then coat the wood with chloride of calcium. As a result, in the outer layers of the wood, gypsum 

 (sulphate of lime) is formed together with chloride of iron. The wood becomes, simultaneously, impermeable 

 to water and adopts a metalic shine. 



II. Boiling: - 



(a) Boiling of building material in salt water or in a solution of borax was customary in olden 

 times. It seems to be, nowadays, a method rarely practised. 



(b) Boiling of logs (e. g., walnut logs) with exhaust steam, resulting in the discharge of a black 

 juice from the logs, is frequently seen abroad. The process is supposed to remove or destroy, also, the 

 albumen and the starch contained in the wood, on which certain fungi are said to feed. 



(c) FRANKS' mixture CONSISTS of 95 per cent liquid manure and of 5 per cent lime. It is pumped 

 into large vats, within which the wood is boiled for 3 to 8 days. The liquid enters to a depth of about 

 3 inches and darkens the wood to a mahogany tint. 



