H A strong Vessel whereinto the Lixivium remaining after the generating (or shooting) of the Salt-petre, is put.
The way to purifie the Crude Salt-petre.
When all these things are thus done, and the Lixivium that swims at the top of the Salt-petre is taken away, lift up those Vessels, or Brass Pans, containing that salt, and turn them up and down in some convenient place, that so the residue of the Lixivium, that lies as yet in them may flow, or run clearly out, into another Vessel set thereunder.
This done, take the Salt-petre out of the Coolers, or out of the Coppers (or Brass Pans) with an Iron Spatula, or rather with such an Instrument as your Plasterers use (eine telle, a Truel) and put it in a Tub that has a hole in the bottom thereof, that so the Lixivium may be perfectly separated therefrom. They that sell that crude Salt-petre, and not at all purified, for the Salt-petre Boilers, do pour thereon pure (or clear) Well-water, by the means of which, it is made more white, that which is thencefrom separated they do again mix with other stronger Lixivium and so boil it up for the following use.
But if you have a mind to purifie this crude Nitre from its salt, and all its Impurities, that it may be rendred fair, and white, you are to proceed this following way:
Take almost as much Well-water as is sufficient for the dissolution of the Salt-petre, put it in the purifying Copper Vessel, first cleaned with water, and dried with a cloth, and put the fire under it, and make it most exceeding hot, then throw in your Salt-petre by little and little, and in pieces, continually stirring the Salt-petre that sticks at the bottom with a spoon, that it may be the easier, and sooner dissolved; this only is to be observed, that there is required a more gentle fire, while the Salt-petre is cast into the Copper, so as the water may be kept always hot. When all the Salt-petre is almost dissolved in the water, promote the boiling thereof, by augmenting the fire, then try if there be any salt in a (biggish) gross form, residing in the bottom of the Copper Vessel, which if you find to be, (for indeed, the Salt-petre it self is not so very easily dissolved, nor doth its being admixt in a more copious manner, at all benefit the Lixivium) take it forth with a Spoon, (or Ladle.)
This done, separate the Scum swimming at top of the boiling water, then have ready a Brass Vessel that will hold about ℥j.ss. of Liquor, fill it half full with the Lixivium, set the Vessel in cold water to cool, and you shall find your Nitre presently to Crystallize, or shoot therein.
Hereby may you try whether your Purgative water be strong enough, or not; for if it be stronger than is fit, you will find a little skin spread it self over the matter contained in the Vessel, and when it comes to be so, add thereunto more hot water, keeping the fire in that degree of heat, as may suffice to keep the water contained in the Copper, gently boiling.
Now when you have kept it thus boiling for some season, try the goodness of your water again, after the aforesaid manner; and if you shall find a Crystallization therein, and no Concretion, or heaping-together, leaving a gaping, or chap in the midst, the business is well done; but if it be otherwise (than thus well done) so that it be wholly shut in (or gathers a skin all over) at top, pour on hot water, until your Matters come to succeed after the manner aforesaid.