PRESERVATION OF TIMBER. 107 



4. To counteract its alternate contraction and expansion in conse- 

 quence of the varying state of moisiness and temperature of the 

 atmosphere. 



5. To diminish its inflammability and combustibility. 



6. To give it a variety of permanent colors and odors. 



In the whole of his experiments M. Boucherie set out from this 

 proposition, the truth of vv^hich appears indisputable and to require 

 no comment, viz : That all the changes which wood undergoes pro- 

 ceed or depend upon the soluble matters which it contains. In confor- 

 mity with this idea, the first step towards giving durability to timber 

 was, either to render these matters insoluble and inert, or to remove 

 them entirely. M. Boucherie, therefore, in his first trials sought to 

 render the matters insoluble by charging the wood with a substance 

 capable of combining chemically and forming a precipitate with the 

 soluble matter left by the sap. To resolve this problem, M. Boucherie 

 investigated the reactions between the soluble matter of wood, which 

 it was his object to precipitate, and a variety of low-priced chemical 

 agents. He found that the pyrolignite of iron combined the greatest 

 number of desirable properties : it is very cheap, the oxide of iron 

 forms stable compounds with the greatest number of the organic 

 substances which are found in the sap of vegetables, and, to conclude, 

 the crude pyrolignite contains a notable quantity of creosote. 



The facts upon which M. Boucherie relies as proving the preser- 

 vative powers of the pyrolignite of iron flow from numerous experi- 

 ments performed either on vegetable substances which in themselves 

 readily and rapidly undergo changes ; or upon billets of wood of 

 diflferent kinds. A quantity of flour, the pulp of carrots, beet-roots, 

 &c., impregnated with the pyrolignite resist decomposition in a very 

 remarkable manner in contrast with the same substances when they 

 have not been prepared in any way. 



The wood which was selected for trial, was generally of the most 

 perishable kind. In December, 1838, several empty hogsheads and 

 barrels made of the best timber unimpregnated and impregnated with 

 the pyrolignite were placed together in the dampest parts of the great 

 cellars of Bordeaux. In August, 1839, it was easy to see that the 

 unimpregnated tubs were already deeply stricken, and after from 

 two to three years they fell to pieces with the slightest force ; the 

 casks made of the prepared wood, however, were as sound as on 

 the first day of the experiment.* 



M. Boucherie concluded from his experiments instituted with a 

 view to the settlement of the question, that about ^^'^th of the weight 

 of the wood in its green state of the pyrolignite was adequate to 

 precipitate and render insoluble all the principles obnoxious to change, 

 which were contained in the woody tissue. 



M. Boucherie, while he regards the pyrolignite of iron as at once 

 the most powerful, and one of the cheapest preservatives of timber, 

 nevertheless indicates several soluble salts, which are readily avail- 

 able in consequence of their low price, and also very effectual when 



* Comptes Resdas, t. ii. p. 8[«& 



