Lees and after that another, until you have weigh'd a Centner of the Lees, then with Pincers take the Lees and the little Scale, which must have room for a Centner of Lees in it) from the Ballance, and set it upon a foot made on purpose over a little warmth, or upon a piece of Iron-plate or Lamin, and hold a large Candle under it, and the Lee will begin to boil in the little Scale, and let it boil till all moisture is boil'd in, and the remains becomes yellow-white, and hardish, then lift it off, and put it in the Ballance again, lay as much of the proof∣weight against it as it weighs, so you may see how much [Section. 3] Salt-Petre a Centner of this Lee will yield; only observe, If you make your proof too hot, then the Salt-petre will be of a black-brown, and so spoil'd, then make it anew, that the Proof may be right.
But that you may know whether it be Salt-Petre or [Section. 4] Vitriol, take with a knife, out of the little Scale, some of the rest of the matter, and lay it upon glowing Coals, and when it melts and burns, and is sharp upon the tongue and cold, then it is Salt-Petre, but if it be Salt and no Salt-Petre, then it sparkles upon the Coals, and will flow, and is upon the Tongue like a common sharp Salt.
[Section. 5] By such proof (perform'd with diligence) it▪ doth many times prevent that no unprofitable or saltish Earth is brought in or made to Lees, or boyl'd off (as I will shew in my following Instructions.)
After the Proof is made, observe diligently when the Salt-Peter doth burn, whether it leaves behind much fe∣ces or dregs like Ashes, which will not burn, and this is Salt. For, if it be found thus, though the Earth be pre∣ty rich in the Proof, yet it is not to be accounted so good, as if the proof were poorer, and burned clear off upon the Coals, therefore the Salt by it is not so good, but it must alwayes be separated from the proof, for it