This section is from the book "The Tinman's Manual And Builder's And Mechanic's Handbook", by Isaac Ridler Butt. Also available from Amazon: The Tinman's Manual And Builder's And Mechanic's Handbook.
Oak, Maple, Beech, and Chestnut make the best quality. Be-tween 15 and 17 per cent, of coal can be obtained when the wood is properly burned. A bushel of coal from hard wood weighs between 29 and 31 lbs., and from from pine between 28 and 30 lbs.