112 PRESERVATION OF TIMBER. 



pregnate the wood with a variety of beautiful colors, and thus to 

 give even the most common kinds tints that will admit of their being 

 used in the construction of costly furniture. The pyrolignite of 

 iron alone gives an agreeable brown tint that harmonizes excellently 

 with the natural color of the harder parts of so many trees which 

 usually resist penetration. By following up the pyrolignite with an 

 infusion of nutgalls or oak-bark, the mass of the wood is penetrated 

 with ink, which presents a black, blue, or gray color, according to 

 circumstances; a solution of another salt of iron succeeded by one 

 of prussiate of potash will cause a precipitate of prussian blue in the 

 wood, &c. ; in short, by the numerous reactions of this kind with 

 which chemistry is familiar, a great variety of colors may be ob- 

 tained. 



Among the number of useful properties communicated to wood by 

 impregnation with saline solutions, that of being rendered little apt 

 for combustion ought not to be omitted. M. Gay-Lussac was the 

 first who thought of rendering vegetable tissues incombustible by 

 means of saline impregnations.* By incombustible, we are not to 

 understand unalterable by a red heat ; for every one must see that 

 the protecting power of no salt can extend so far as this ; but tissues 

 which take fire very readily, and burn with great rapidity, cease 

 from giving any flame, and merely smoulder, after they have been 

 impregnated with certain salts ; they take fire with difficulty, go 

 out of themselves, become charred, and are incapable of propagating 

 fire. And this is exactly what happens with wood which has been 

 properly charged : it burns, and is reduced to ashes with extreme 

 slowness, so that two huts exactly alike, built one of charged wood, 

 and the other of ordinary wood, having been set fire to at the same 

 moment, the latter was already burned to the ground, when the in- 

 terior of the former was scarcely charred. f 



The ingenious process of impregnating wood by the way of vital 

 inspiration is not without certain objections. In the first place, it 

 can only be performed at those periods of the year when the sap is 

 in motion, and the trees are covered with their leaves. This time, 

 however, is limited to a few months of the year, and the usual prac- 

 tice being to fell timber in the winter, wont and usage are opposed 

 to cutting down trees in the spring and autumn. To meet these 

 objections, M. Boucherie engaged in new experiments, which led 

 him to a means of impregnating timber at all seasons, in winter as 

 well as spring and autumn, and in a very short space of time ; this 

 second method is applicable to wood that has already been squared 

 as well as to the round trunk, provided it has been recently felled. 



To impregnate timber by this process, the logs are placed verti- 

 cally, and the upper extremities are fitted with an impermeable sack 

 for the reception of the saline solution destined to charge them ; the 

 fluid enters from above, and almost at the same moment the sap is 

 Been to begin running out below. There are some woods which 



 Ann. de Chimie, t. xviii. p. 21], 2e sirie. 

 t Idem, t. l^xiv. p. 1.52, 3e s6rie. 



