The earth and ashes left, after the weak Lixivium (hath past through them) are to be laid up in some convenient place, and there kept for four years or more, that so they may be again apt to yield a-new more Lixivium by extraction; which, that it may be the better and easier done, there must be made in them (many weeks afore they are wrought upon) by digging some Pits or Gutters, that so they may be freed by the heat of the Sun from that moisture wherewith they as yet abound. Nor do the ancients so much wander from the Truth in that they suppose it much better and more profitable to keep all the earth under a roof or shed, and that it will be far sooner reduced unto a fitting goodness, than to lie open to the weather, for much of the Salt-petre is corrupted (or spoiled) with an abundance of moisture, especially with the Rain it self: For it needs only a little wetting whereby it may be generated, and extreamly shuns, or is injured by too much moisture.
Besides these ways, there are many that mix with this earth that is yet contained in the Tub the Saw-dust of Firr, or some other Wood (the height of) a Fingers length (on it): And they perswade that Salt-petre is also generated and multiplied from that fatness which is mixed with the Saw-dust, and that the earth prepared on this wise can be so changed in a years space (so it be kept in a dry place) that it may be again made use of as afore. Yea and they suppose too that they can do much here, if they pour upon such a barren (or lean) earth, thus lying in a dry place, the reliques or remains of the dyes, which the Dyers are otherwise wont to throw away, and evident it is that they are aluminous, but yet not so frequently.
Besides such waters of the Dyers they are wont also to mix soot with their earth, (yea and the ashes too of which Lawndresses do commonly make their Lee;) that so it may be made the more fruitful and may be the sooner brought to use.
This only is to be noted, that there are sometimes found earths that give a thick black Lee, which being used by it self is too fat, to which is to be added a leaner and dryer earth, that so the Salt-petre may be the better and more plentifully generated.
The way therefore how, and the instruments by which crude Salt-petre is purifyed, is shown by the 6 and 8 Figure (in Lazarus Ercker’s Book I think he means.)
The manner of purifying the gross and blackish Salt that comes out of the Salt petre.
That black or rather ashy colour Salt, which is found in the Copper while the nitre is prepared by boiling, and likewise in the narrow Tub or Vessel, may be reduced into very good Salt, and very convenient for daily use, and no ways at all hurtful to Man, if it be but duly purified; which said purification is to be thus ordered.
The Copper being well cleaned fill it with most clear Well-water, put fire under it and make it boil, throw in the said Salt by times (not all at once) into the boiling water, that so it may be dissolved; which, that it may be the sooner and better done, stir it continually with a Spatula, when you think that it is all dissolved pour out the Lixivium into some Vessel or Tub, & you shall see the grosser part will settle to the bottom, and the Lixivium will clear up: When you perceive this, pour this clear Lixivium again into the cleansed Copper, and boil it so long till the Salt settles to the bottom, which take out of the said Copper with a perforated Ladle, and put it in a Basket that is placed over the Copper, that so all the superfluous Lee or moisture may again run down into the Copper, and yields (or leaves) the Salt perfect and dry.
Some there are who afore they use this Salt about domestick affairs, do decrepitate it first, and perswade themselves that it becomes thereby the more virtuous (or strong.)