The Haycock boiler was:

The Haycock boiler, significant in the historical development of steam technology, was indeed used around 1720. This design represented an early stage in the evolution of steam boilers and was primarily utilized for producing steam for industrial use, such as in engines and other machinery.

While other types of boilers have different construction methods and designs, the Haycock boiler specifically featured a cylindrical shape with a large, conical top, which was crucial for creating steam from water. Its use in the early 18th century marks a transition from earlier heating technologies, showcasing advancements in engineering and the increasing demands of the industrial revolution.

This context helps illustrate the importance of the Haycock boiler during that era, as it laid the groundwork for future innovations in boiler technology. The other options refer to different characteristics that do not apply to the Haycock boiler, helping to frame its unique historical significance in the broader spectrum of boiler design.