Early briquettes were large and brick-shaped. They could be stacked, or even built into walls. The Antarctic expeditions of both Shackleton and Scott took large quantities of these briquettes with them and used them to build pony stables. As the ponies were eaten, as planned, the stables could be dismantled and used for fuel. Phurnacite briquettes later adopted a squared oval shape. This regular shape packed well as a good firebed, with plentiful airflow. They are also easy to mechanically feed, allowing the development of automatically controlled heating boilers that could run for days without human intervention.