Ketene Dimer: Ketene Left to Polymerise, the 126-127 °C Liquid (Thorpe 1912)

Kept for a while, ketene turns into a dark liquid. Its chief part is a colourless, pungent liquid boiling at 126-127 °C, C4H4O2: two ketene molecules joined. Source: Thorpe, Dictionary of Applied Chemistry vol. 3 (1912), Ketenes. Unknown: how long and at what temperature, and how the 126-127 °C liquid is separated. Thorpe gives none of these, so they are linked to unknown heads. Metal chlorides or tertiary bases speed the change; that route is another blueprint. Picture drawn by Youblob.