How did William Morton make anesthesia?

Answer 1

He went to Harvard and learned in a chemistry class that diethyl ether was an anaesthetic. It was known to be one well before Morton, and had been used as one before Morton demonstrated it.
Morton became famous by arranging the first public demonstration of ether anaesthesia in dentistry, and then set about trying to patent it and claim credit for inventing it. This never quite worked as there was so much evidence he hadn't come up with the idea.
He became associated with having invented it due to his public demonstration of it and his own vigorous campaign to be acclaimed as the inventor of it.
Crawford Long was the first to use ether as a general anaesthetic, and there were witnesses and Long's first use of it is not disputed, but he didn't publish his findings until after Morton's demonstration of it. To be fair to Morton, he'd have had no reason to know Long had already done it. But even when he found out, he continued to claim the right to be called the pioneer of it.