Sentence:  The Abbe had, in the district of Latera, observed that in a <WSD>mephitis</WSD> of hydrogenous sulphurated or hepatic gas, a slow combustion of phosphorus took place, with the same resplendence as in the atmospheric air. 
Meaning of the word marked with <WSD> tags:  A poisonous or foul-smelling gas, especially as emitted from the earth; an unpleasant (smell).