Sentence:  ... I allude to the <WSD>æthers</WSD> formed by the union of fatty acids with different alcohols. ... With regard to the fatty <WSD>æthers</WSD> themselves, I prepared them generally by M. Berthelot's method, by heating the alcohol and the acid for a day at 392°F. in a tube hermetically sealed; the product was mixed with a little <WSD>æther</WSD>, and it was digested some time with slaked lime in the water-bath, to separate the free acid from the neutral compound. 
Meaning of the word marked with <WSD> tags:  Any of a class of organic compounds containing an oxygen atom bonded to two hydrocarbon groups.