Threshing is the process of loosening the edible part of grain (or other crop) from the straw to which it is attached. It is the step in grain preparation after reaping.
2)
A goldsmith USES the non-luminous ZONE (outermost zone) of CANDLE flame to melt gold and silver because it is the hottest part of the candle flame and has most temperature.
3)
White PHOSPHORUS is highly reactive, and spontaneously ignites at about 30°C in moist air. It is usually stored under water, to prevent exposure to the air.