Solder. It 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 solder presumably used by John F.W. Herschel or his children (it may even have been used by John F.W. with his children) to build apparatus for experiments.