The manner of preparing the Liquor, out of which Salt-petre may be made by Boiling.
First of all, pour your second weaker Lixivium into your Copper, and set it a boiling, then let your second stronger Lixivium run thereinto by little and little; and then lastly, the first Lixivium it self, and which is the chiefest of all, until the Copper be almost filled, and the Lixivium be boil’d enough to shoot.
And now when you perceive that your Liquor is made strong enough by boiling, put in a Brass Ladle perforated (or full of holes) several times, even to the bottom of the Copper, and if the Lixivium lets fall out of it any Salt, you will find it at the bottom, the which you may take up with your Ladle.
Note also, That the Scum which at the end of this Boiling is plentifully gathered, must be carefully taken away: Now then try the readiness of your Lixiviums Crystallization, on this wise: Put either two or three drops on a cold Iron, or on a Polish’d Plate of Iron, and if it stands, or grows hard; that is, if when you turn the Iron up and down, it does not run (or flow) down, these are signs of the fitness of your Liquors Crystallization. Or else, you may put some of the Lixivium in a Brass Vessel, and set it in cold water, and so you shall see whether the Liquor be fitted enough to Crystallize; for assoon as ever the Lixivium shall be cold, there will be plenty of Salt-petre generated: Nay, even the very Brass Spoon it self denotes the goodness of the Liquor, it being put into the Liquor, and again taken out, it will show it sticking on it, as if it were Oil.
Out of a Centenary, or hundred weight of Liquor thus perfectly prepared, there will proceed more than seventy pound of Salt-petre.
The way of rightly using the Liquor for the Generating of a more Crude Salt-petre.
Pour your Liquor prepared after the afore-shown manner, out of the Copper into a narrow Tub, or Vessel, made of Firr, or Pine-tree wood; wherein let it remain quiet, till it be a little refrigerated, and the muddiness, or slimyness [Limus] appear, and you find that the salt sticks on in Granes to the sides of the Vessel; now when you perceive your Lixivium so cooled, as that you can put your finger thereinto without burning, pull out the Plug, wherewith an hole made in this long Vessel, about a span’s heighth from the bottom, was shut, or stopt, and so let the Liquor run forth, into very great Wooden Vessels, and deep, purposely made for such a business; or else into Copper Pans, buried almost (up to their Necks) in the earth, (for the cooler the place is, which they stand in, so much the better, and the more plenty of Salt-petre is gathered, and Crystallizeth) and you will find that your crude Salt-petre will shoot therein, the thickness of almost two fingers breadth, partly of a whitish colour, partly yellow, and partly blackish.
After that this boil’d Liquor hath stood for two days, and so many nights in the Vessel, the Lixivium of the Salt-petre which swims at top, must be taken away, which you may mix with the strong Lixivium, and pour a second time upon Ashes, for else the Lixivium will contract too much fatness, and there will be no Salt generated.