[ 29 ] filling them about two thirds full, then set these tubs in a cool cellar, and let them remain there twenty-four hours at least, if it has been boiled sufficiently the Salt-petre will be formed into beautiful crystals, but somewhat foul; pour off the liquor that remains, and set the tubs on one edge to drain; this liquor is called the mother of lye, and should be returned into the kettle with your next boiling, or may be further boiled down by itself, and set out to crystalize again as it is very strong of Salt-petre;if there should be no Salt-petre settled in your tubs after standing the time directed, it is a sign your liquor has not been boiled enough, therefore you should return it again into the kettle, and boil it about one half away, proceeding as has been already directed to separate the sea salt, &c.
Sixthly, Of the Refining.
When you have a sufficient quantity of Nitre made, you may proceed to refine it, which is performed thus: Put your Nitre into a boiler that will hold about one third more than your quantity of Nitre, add as much water as will cover the whole mass one inch, after it has soaked through it, put it on a gentle fire, keep continually stirring it quite to the bottom till the Salt-petre is all dissolved, take off the foul scum as it rises, which you must continue to do as long as any appears, when the scum has nearly done rising, the sea salt must be taken from the bottom of the kettle with the skimmer, and which is nearly on sixth part of the Salt-petre; it will be proper for you to taste this as you take it out of the kettle, or you will be apt to be deceived by its appearance while wet,
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