24 



butyric, crotonic, and valerianic acids; acetaldehyde, furfuraldehyde, 

 methyl-propyl ketone, methyl-ethyl ketone, methyl formate, methyl 

 acetate, etc., have been recognized. 



NONCONDENSABLE GASES. 



The gases produced during distillation constitute from 20 to 30 per 

 cent of the wood and consist of about 53 per cent of carbon dioxid, 

 38 per cent of carbon monoxid, 6 per cent of methane, and the remain- 

 ing 3 per cent of nitrogen, hydrogen, etc. These gases are of such 

 low illuminating power that they are usually either burned under the 

 boilers or retorts or are wasted. 



CHARCOAL. 



The charcoal left in the retort when distillation is complete con- 

 stitutes from 20 to 35 per cent of the original weight of the wood, the 

 quantity depending on the kind of wood and the manner of heating 

 the charge. The physical qualities and chemical composition of 

 charcoal are governed chiefly by the temperature at which the wood 

 is heated. When heated to about 280 C., wood begins to be friable 

 and has a brownish black color. At 310 C: it is friable, takes fire 

 readily, and is black in color. The coal becomes harder with further 

 rise of temperature and is less readily ignited. As it is only 25 per 

 cent as heavy as the wood from which it is made charcoal presents 

 some advantages as a fuel, because of lower transportation charges. 

 A good charcoal should be thoroughly burned without being brittle 

 and should show the woody texture distinctly. The fracture should 

 be conchoidal, lustrous, and quite black. It should have few cracks, 

 the specific gravity should be high, and it should burn slowly without 

 flame or smoke. 



Charcoal is chiefly used in the manufacture of charcoal iron, for 

 which purpose it is especially valuable, because of its low phosphorus 

 and sulphur content. It is also used to some extent as a t domestic 

 fuel and as an absorbent and clarifier. 



TAR AND OILS. 



WOOD TAR. 



The crude wood tar produced when wood is distilled in retorts 

 varies from 3 to 10 per cent of the wood. The portion separated from 

 the crude pyroligneous acid by settling and that skimmed off of the 

 top of the neutralized acid are united, and, after washing with water, 

 may be sold in the crude state as u raw tar" or as " re tort tar." It is 

 used for preserving wood, for making roofing felts, as an antiseptic, 



[Cir. 36] 



