The speech standard of the Ming and Qing empires was called Mandarin language by European missionaries, translating the Chinese name Guanhua (the language of the officials) for this speech standard, which was current already in the Ming Dynasty.
Producer gas is made by blowing air through an incandescent fuel bed (commonly coke or coal) in a gas producer. The reaction of fuel with insufficient air for total combustion produces carbon monoxide (CO); this reaction is exothermic and self-sustaining.
Burning natural gas is exothermic. An exothermic process releases heat, causing the temperature of the surrounding area to rise. Burning gas releases heat and warms whatever is around it, so it's exothermic. An endothermic process absorbs heat and cools the surrounding area.