216 VINEGAR, CIDER, AND FRUIT-WINES. 



the cellulose is so closely packed that very little room is left for 

 the retention of air. The following table exhibits approximately 

 the specific gravity of various woods : 



The content of ash is not the same in all woods; it varies 

 considerably in different parts of the same tree and also with its 

 age. According to Violet, in the cherry tree the content of ash 

 is greatest in the leaves (about 7 per cent.), next in the lower 

 parts of the roots (5 per cent.) ; considerably greater in the bark 

 than in the Wood, in the former from 1.1 to 3.7 per cent., and in 

 the latter 0.1 to 0.3 per cent. Saussure found in the bark of the 

 oak 6 per cent., in the branches 0.4 per cent., and in the trunk 

 0.2 per cent, of ash. The ash consists chiefly of carbonates of 

 calcium, potassium, and sodium, further of magnesia and the 

 phosphates of different bases. 



The average composition of 100 parts of air-dry wood is : car- 

 bon 39.6 parts, hydrogen 4.8, oxygen and nitrogen 34.8, ash 0.8, 

 hygroscopic water 20 ; and that of artificially dried wood : car- 

 bon 49.5, hydrogen 6, oxygen and nitrogen 43.5, ash 1. 



Decomposition of u-ood. Cellulose when carefully treated re- 

 mains unchanged for a long time, even thousands of years. Wood 

 is, however, subject to greater changes, though under especially 

 favorable circumstances it may last for several centuries. In the 

 presence of sufficient moisture and air the nitrogenous bodies of 

 the sap are, no doubt, first decomposed, and the decomposition 

 being next transferred to the woody fibre, the latter gradually 

 loses its coherence, becomes gray, then brown, and finally decays ; 

 hence, wood rich in water decays more rapidly than dry wood. 



Wood to be preserved should, therefore, be as dry as possible, 

 and the nitrogenous bodies, which can be but incompletely re- 

 moved by lixiviatiou, be converted into insoluble combinations ; 

 tar and one of its most effective constituents creasote mercuric 

 chloride, blue vitriol, chloride of zinc, and many other substances 

 having been recommended for this purpose. Moreover, it has been 

 successfully attempted to produce certain insoluble bodies, such 



