Note 24 — PART VI.

The Retorts should be manufactured of what is called in commerce, iron of the second process. The best cast-iron of this kind, is of a light grey colour, its fracture is granulated and dull, it receives a dent from the blow of a hammer. The cast-iron which exhibits a dark grey or black colour inclining to blue, and presents granular concretions, readily friable, and therefore unfit for vessels intended to stand a long continued heat.