being laid in a heap, are covered with other elixed or drained Ashes, the better to keep them warm; which is reiterated, as long as they make Brimstone.
To make Coperas or Vitriol, they take a quantity of the said Ashes, and throwing them into a square planked pit in the Earth, some four foot deep, and eight foot square, they cover the same with ordinary water, and let it lye twenty four hours, or untill an Egge will swim upon the liquor, which is a sign, that it is strong enough. When they will boyl this, they let it run through Pipes into the Kettles, adding to it half as much Mother-water, which is that water, that remains after boyling of the hardned Coperas. The Kettles are made of Lead, 41 foot high, 6 foot long, and 3 foot broad, standing upon thick Iron Barrs or Grates. In these the Liquor is boyled with a strong Coal-fire, twenty four hours or more, according to the strength or weakness of the Lee or Water. When it is come to a just consistence, the fire is taken away, and the boyled liquor suffered to cool somewhat, and then it is tapp'd out of the said Kettles, through holes beneath in the sides of them, and conveyed through wooden Conduits into several Receptacles, three foot deep and four foot long (made and ranged not unlike our Tan-pits) where it remains fourteen or fifteen dayes, or so long till the Coperas separate it self from the water, and becomes icy and hard. The remaining water is the above-mentioned Mother-water; and the elixed or drained Ashes are the Dreggs, or Caput mortuum, which the Lee, whereof the Vitriol is made, leaves behind it in the planked Pitts.
A further Account of Mr. Boyle's Experimental History of Cold.
In the first Papers of these Philosophical Transactions, some promise was made of a fuller account, to be given by the next, of the Experimental History of Cold, composed by the Honourable Mr. Robert Boyle; it being then supposed, that this History would have been altogether printed off at the time of publishing the Second