PLANT PRODUCTS. FERMENTATION AND FUELS 421 



ture, used in road-making (10 per cent), water (77 per cent), 

 and a little acetone J^p. 349) . The distillate from resinous wood 

 also contains valuable quantities of turpentine, CioHie, an un- 

 saturated hydrocarbon used extensively as a solvent. The gases 

 evolved contain a large part of the nitrogen of the original proteins 

 hi the form of ammonia, which is dissolved out with water. 



When charcoal only is desired, the wood is stacked, covered 

 with turf (Fig. 104), and set on fire. A part is burned, the rest 

 is converted into charcoal, and all 

 the valuable volatile products are lost. 



Properties of Wood Charcoal. 

 Absorption. The charcoal retains 

 the structure a complex network of 

 minute cells of the original wood, and therefore has a surface 

 which is vast in proportion to the amount of material it contains. 

 Upon this surface it is capable of taking up or of adsorbing many 

 times its own volume of gases, especially of the more condensible 

 ones. Thus, boxwood charcoal takes up ammonia (90 volumes), 

 hydrogen sulphide (55 volumes) , and oxygen (9 volumes) . 



The adsorption is extremely rapid and, in the case of a conden- 

 sible gas contained in small quantity in air, practically complete. 

 For this reason, charcoal and other substances with very finely 

 divided surfaces are used as adsorbent materials for industrial 

 gases and vapors (compare silica gel, p. 360). 



The toxic gases employed in the Great War are also readily 

 adsorbed by charcoal. Hence the canisters of gas masks con- 

 tain layers of porous charcoal, together with granulated soda- 

 lime and potassium permanganate, which react chemically with 

 certain of the noxious gases liable to be present. During the war 

 vast strides were made in increasing the adsorptive power of 

 various kinds of charcoal by modifications in methods of carboniz- 

 ation, the most efficient of all charcoals being dense varieties 

 derived from cocoanut shells and fruit pits. Canisters packeC 



