Sentence:  On closer inspection it appeared that steel <WSD>annealed</WSD> at 100° is, cæteris paribus, more easily soluble than glass hard steel; steel <WSD>annealed</WSD> at 200° more easily soluble than steel <WSD>annealed</WSD> at 100°, and steel <WSD>annealed</WSD> at 360° more easily soluble than steel <WSD>annealed</WSD> at 200°. ... These curious results were substantiated by <WSD>annealing</WSD> one-half of short glass hard rods (ca. 5cm in length) at red heat on dissolving in HCl, the diameter of the soft length is diminished more rapidly than the diameter of the hard length. 
Meaning of the word marked with <WSD> tags:  To subject to great heat and then (often slow) cooling, and sometimes reheating and further cooling, for the purpose of rendering less brittle; to temper; to toughen.