FUEL AND CHARCOAL. 



107 



employed on the Continent. If the fire is steady and regular, the 

 slower the process the better the yield. For gunpowder-charcoal, 

 however, and acetic acid, iron or brick ovens are mostly employed. 

 The best gunpowder-charcoal is produced from light woods, such 

 as Willow, Buckthorn, or "Dogwood" (Rhimmis Frdngida'), and 

 Alder. Charcoal is darker, heavier, a better conductor of heat 

 and electricity, less easily ignited, and gives out greater heat in 

 burning, the higher the temperature at which it has been made. 

 The proportion of charcoal yielded is greater (24 to 30 per cent.) 

 with a slow process, that of the volatile products with a rapid 

 one. From experiments with Hornbeam, Alder, Birch, Rowan, 

 Beech, Aspen, Oak, Buckthorn, Silver Fir, and Larch, we find the 

 yield of charcoal to range from 20 per cent, with slow, to 34*6 per 

 cent, with quick distillation; the total distillate from 43 to 53 

 percent.; the pyroligneous acid from 47 -5 in the hardwoods to 

 38 in the conifers; and the tar from 2-9 in Beech to 9 -7 in 

 conifers. In practice only about 18 to 20 per cent, by weight of 

 charcoal is obtained, or about half the volume of the wood. 

 Pyroligneous acid is in England largely manufactured from spent 

 dye-woods, such as fustic, logwood, etc., the charcoal obtained 

 being largely used for packing the meat refrigerators in ships. 

 The products of distillation, under the most favourable circum- 

 stances, are stated as : 



Purer acetic acid is obtained by re-distillation, and, when mixed 

 with certain essences, constitutes aromatic vinegar. Among the 



