Ingot of thallium. Thallium is a poisonous metallic element that is also mildly radioactive. It occurs naturally in soils and is used in various alloys and in certain industrial and manufacturing processes.

This ingot comes from a 15-drawer cabinet found in the Herschel family home in the 1950s. The contents of this and a similar cabinet seem to suggest that they were used by successive generations of the family to store specimens, material and apparatus for carrying out experiments.

This sample of thallium was presumably used by John F.W. Herschel or his children (it may even have been used by John F.W. with his children) as the raw materials for experiments.