230 VINEGAR, CIDER, AND FRUIT-WINES. 



cylindrical space above the retorts (Fig. 54) the content of water 

 can be reduced to 10 per cent., and consequently less water has 

 later on to be removed by evaporation ; besides, the distilling 

 time is shortened, and a larger yield of wood-vinegar obtained. 



Charcoal. 



The substance called charcoal is not pure carbon; it containing, 

 besides this element, hydrogen, oxygen (together with traces of 

 nitrogen), and ash. The composition of charcoal, and conse- 

 quently its properties, vary very much according to the degree 

 of temperature to which the retort has been exposed, the duration 

 of heating, and the variety of wood. 



By heating the wood in the retorts the hygroscopic water 

 escapes first; then, at a temperature somewhat above 212 F., 

 wood-vinegar makes its appearance and gradually increases in 

 strength until its maximum strength is reached at 424 F. ; it 

 then again becomes weaker. Next the formation of tar begins, 

 and inflammable gases now make their appearance. If the opera- 

 tion be continued to the end, the products are : .black charcoal, 

 wood-vinegar, tar, and gases. If distillation is, however, inter- 

 rupted when the greater portion of the wood-vinegar is separated 

 and the formation of tar would commence, charbon roux or torrified 

 charcoal, i. e., a product containing the greater portion of the 

 constituents of the tar and the gases, remains. Experience has 

 shown that torrified charcoal is as well adapted for use in the 

 blast-furnace as black charcoal. The yield is about forty per 

 cent, of the wood used, and being firmer and harder than black 

 charcoal it is better adapted for transport. 



To a product intermediate between wood and torrified charcoal 

 the name red-wood (roasted wood, bois roux) has been given. It 

 is brown, can be worked like wood, is but slightly hygroscopic, 

 highly inflammable, and has nearly double the heating power of 

 wood. Its average composition is : carbon 52.6 per cent., hy- 

 drogen 5.8, oxygen (together with nitrogen) 36.6, ash 0.4, water 

 (moisture or constitutional) 4.5. 



For technical purposes charcoals obtained at a temperature of 

 above 51 8 F. are only available, those obtained at a lower tempera- 

 ture containing the so-called brands with a content of carbon of, 



