The deposition of pure zinc is beset with many difficulties,..unless the conditions are closely watched, it is liable to be thrown down in a spongy form... Siemens and Halske have proposed the addition of oxidising agents such as free halogens, to prevent the formation of zinc hydride, to which they attribute the formation of zinc-sponge.
Encyclopædia Britannicavol. XXVIII. 110/2
Originally published as part of the entry for zinc, n.
zinc, n. was first published in 1921; not fully revised.