COMPOSITION OF WOOD. 51 



processes aids in a more uniform or perfect seasoning, it increases the 

 strength of the material. 



Pine "bled" for turpentine is as strong as "unbled." 

 Time of felling, whether season of the year or phase of the moon, does 

 not influence strength, except that summer-felled hard wood rarely sea- 

 sons as perfectly as that felled in the fall, and to this extent an indirect 

 influence may be observed, as well as by the fact that fungi and insects 

 have a better opportunity for developing. 



Warm countries and sunny exposures generally produce heavier and 

 stronger timber, and conditions favorable to the growth of the species 

 also improve its quality. But exceptions occur; neither fast nor slow 

 growth is an infallible sign of strong wood, and it is the character of 

 the annual ring, rather than its width, and particularly the proportion 

 of summer wood, which determines the quality of the material. 



VI— CHEMICAL PROPERTIES OF WOOD. 



Wood dried at 300° F. is composed of over 99^per cent of organic and 

 less than 1 per cent of inorganic matter; the latter remains as ashes 

 when wood is burned. 



Wood consists of a skeleton of cellulose, permeated by a mixture of 

 other organic substances, collectively designated by the name of lignin, 

 and particles of mineral matter or ashes. 



Cellulose is the common substance of which plant cells form their 

 cases or walls; in flax, the entire fiber is almost pure cellulose, but the 

 amount of cellulose obtained from wood, by the common processes, 

 rarely exceeds one-half of its dry weight. Cellulose is identical in 

 composition with starch, but unlike the latter it resists alcoholic fer- 

 mentation, though the plants themselves, as well as decay -producing 

 fungi, are able to reconvert it into starch, from which it seems origi- 

 nally derived, and also to change it into various forms of sugar. 1 Lig- 

 nin is as yet a chemical puzzle. The substances forming it are carbo- 

 hydrates like cellulose itself, but of slightly different proportions and 

 distinguished by greater solubility in acids, and by other chemical 

 properties. 



In 100 pounds of wood (dried at 300° F.) and of cellulose the follow- 

 ing proportions are found : 



Carbon ... 

 Hydrogen 

 Oxygen. .. 



Wood. 



Pounds. 



49 



6 



44 



Cellulose. 



Pounds. 

 44.4 

 6.1 

 49.3 



1 Chemists have succeeded in producing reconversion into grape sugar, and though 

 the methods thus far employed are expensive, it is to be expected that in the near 

 future wood will become the principal source of both vinegar and alcohol. 



