92 



OF WOOD IN GENERAL 



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, 

 Eowan, 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 per cent. ; the pyxoligneous 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 gas manu- 

 factured on the Continent by the distillation of wood consists, like 

 coal-gas, of carbon-monoxide, hydrogen and hydrocarbons such as 

 acetylene, olefiant gas, benzene, etc. That from Silver Fir {Abies 

 "pectinata), for instance, contains carbon-monoxide 22-3 to 61*8 per 

 cent, by weight, hydrogen 18-4 to 48-7, heavy hydrocarbons 6-5 

 to 10-6, and hght hydrocarbons 9*4 to 35*3 per cent. The products of 

 distillation, under the most favourable circumstances, are stated as : 





Charcoal. 



Tar. 



Crude 

 Pyi-oligneous 



Acid. 



Pure Acetic 

 Acid. 



Birch, 



22-4 



8-6 



45-0 



4-47 



Beech, - 



24-6 



9-5 



44*0 



4-29 



Oak, 



26-2 



9-1 



48-0 



8-88 



Juniper, - 



22-7 



10-7 



45-8 



2 34 



Silver Kr, 



21-2 



13-7 



41-2 



2-16 



Scots Fir, 



21-5 



11-8 



42-4 



2-14 



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

 with certain essences, constitutes aromatic vinegar. Among the 

 acetates prepared on a large scale from pyroligneous acid are those 

 of lime, the brown containing from 60 to 70, and the grey from 

 80 to 85 per cent, of acetate. In the preparation of these naphtha 

 is recovered; and from this, by neutrahzing with lime and re- 

 distilHng, wood spirit or methyl alcohol. Wood-tar, used for 

 creosoting wood and in the manufacture of roofing-felts, is a thick, 

 dark, viscous material, containing from 5 to 20 per cent, of acetic 

 acid, from 30 to 65 per cent, of pitch, and from 20 to 45 per cent, 

 of tar-oils. Prom these last, creosote, a colourless, highly refracting 

 oil, with a specific gravity of 1-04, boiling at 406° P., and paraffin, 

 used for candle-making, are obtained, by neutrahzing with car- 

 bonate of soda and further distillation. 



