Dictionarium polygraphicum. Copperas, coperas.

Dictionarium Polygraphicum:
Or, The Whole Body of Arts Regularly Digested.
Vol I.
London: Printed for C. Hitch and C. Davis in Pater-noster Row, and S. Austen in St. Paul's Church Yard. MDCCXXXV.
1735
A mineral form'd in copper mines, and which is properly a kind of vitriol.

Copperas is purified and prepar'd in the same manner as alum and salt petre, by passing thro' several lixiviums till it be wholly reduc’d to crystal.

There is Copperas of England, of Pisa, Germany, Cyprus, Hungary and Italy; which only differ from each other in colour and perfection, being all the same mineral.

White Copperas is the Copperas of Germany, calcin'd, laid in water, then filtrated and reduc’d to salt; of which as it coagulates, they form cakes of forty or fifty pounds each. Such are those brought from Goslelar in Germany.

The saxon Copperas, before it is whiten'd, is of a bluish green, clear and transparent.

The English Copperas is of a fine green; that of Cyprus and Hungary of a sky blue, in pieces cut like the point of a diamond; that of Pisa and Italy is likewise green, and the last is as transparent as glass.

Copperas is of considerable use in many preparations; but especially in dying. The hatters also use it in their dye, and this and galls are the ingredients that compose writing ink.

The ordinary English Copperas is made of a kind of stones found on the sea shore in Essex, Hampshire, and so westward, ordinarily call'd gold stones, from the colour; they abound with much iron.
To prepare the Copperas from them, they are laid in heaps or beds under ground. In process of time, they swell and ferment, and by degrees a humour distils out, which drawn into a cistern, and being afterwards boil'd, in the boiling shoots into those crystals we see it in.