What remains behind of the Lixivium in the Copper, you may boil it up like as you would any other Lixivium appointed to be Crystallized, then pour it out into the Vessels destinated to that purpose, and you shall see Salt-petre to be generated in them; for seeing the said Salt proceedeth out of the Salt-petre, this Lixivium cannot be wholly void of Salt-petre, and therefore may it be separated from that Salt by the aforesaid way, and be purified.
But you are to note here, that where there is too great a quantity of Salt-petre permixt with the said Salt, or that the Salt it self is too black and impure, that Salt cannot get its due lustre and whiteness by barely one such a purifying Operation, and therefore there is requisite a reiteration of this Operation, so that it be again dissolved in new water, and be purifyed, whereby it may become altogether white.
However, such a black and impure Salt, may be purified even by this way (following.) Pour the solution it self, while ’tis yet hot, (the water I mean in which the Salt is dissolved) upon the ashes which a Lixivium hath been already poured on before, and you shall see the Salt Lixivium to be wholly purified: But yet all the Salt which is extracted thence, is not sufficiently white, but that which is gathered last of all is yellowish, and therefore must be yet once again purified. Note also here, that when such a Lixivium of Salt is poured on the ashes, they must be well edulcorated (after the operation is finished) least the Salt sticking in the Reedy or Bull-rush-bottom should give an unfitting saltness to the Lixivium that is next poured thereupon.
And thus have you the common method of boiling and preparing Salt-petre, in which you meet with what may be well disallowed or rejected, viz. it is extreamly tedious, nor is it at all gainful, for out of a centenary of Lixivium, we have no more than three or four pound of Petre; to get which too, all the rest of the water must be done off by evaporation, which is a long time doing, and requires no small costs. Yet I will shew in what follows, by what means this inconvenience may be prevented, which I have proved by mine own experience.
The way of augmenting the Crude Lixivium afore its boiling.
The Salt-petre boilers have hitherto variously sought after the way of augmenting (or fortifying) the Lixivium of Salt-petre, that is, of causing a more plentiful provenue of Salt-petre, in the Water remaining of the extraction of Salt-petre, but in vain, because they were ignorant of the lesser proof which all things here are tried by. Its augmentation is done on this wise.
Take of a Lixivium, a Centenary of which contains iiij. ℔. of Nitre, pour so much of it as a Tub or Vessel will hold, upon new earth, let it stand for twelve hours; then draw off the Lixivium, and as much as you find wanting of what you poured on (which may easily be known by the emptiness of the measure which it was in, afore you poured it on, and in which it is now gathered or received again) pour so much simple water on the Earth, which draw off in like manner, and mix it with the Lixivium, and you will then have the same quantity that you had in your Vessel afore. This done try the Lixivium by the lesser experiment or proof and you will find it to contain vj. ℔. of Nitre. Pour this Lixivium that contains in it vj. ℔. of Nitre upon other new earth, and proceed on the manner aforesaid, and you shall have your Lixivium to contain ix. ℔. of Nitre. You may pour this a third time upon other new earth & proceed on with it after the aforesaid manner, and you shall yet have more Nitre out of a Centenary of Lixivium. But you must be always wary in this Operation, that you draw off, neither more nor less Lixivium from the earth than you had before in the Vessel. These things it pleased me to add, concerning the second pouring on of water, meerly for the experiments or proofs sake, whereby we may be made certain of the augmentation thereof (forasmuch as the Lixivium doth by this means hold in it more Nitre) and that we may be forced to acknowledge its augmentation even in that way. Then after this is done, you may use the weaker Lixivium instead of water, to fill up the first measure, and so the Lixivium will be the easier, and more augmented; and we may in a short time have sufficient quantity hereof for to boil. And although this augmentation of the Lixivium requires a great deal of labour, yet are all the (pains, &c.) recompensed, because we hereby get in one Weeks space, and with less expence of Wood, far more Nitre than by the other common ways: But yet there are requisite more Vessels for this kind of working, wherein the separated Lixivium may be kept.
I will also give the Reader a manuduction here, by what way the boiling of the Lixivium is to be ordered, or contrived: First of all, this is well to be regarded, that forasmuch as a great boiling requires a great quantity of earth, and yet there does not at all times, earth of a like goodness offer it self (especially seeing a Man cannot make proof of it all) upon which the costs and labours (necessary about it) may be well (or at the best hand) bestowed: It seems wholly expedient, not to make such a great Coction (or boiling-trade) but to do it with only three or four Tubs, that so we may choose only the best convenient earth, which we may dig in the Cities (or Towns) out of Houses of long standing, and out of Stables, but yet not too deep: Such a Lixivium as contains in an hundred weight of it eight pounds of Nitre, may be increased to eighteen or twenty pounds, if we proceed according to the aforesaid method. And therefore such Nitre boilers as inhabit those regions where there is scarcity of Wood may give hereunto good heed.
Now the Lixivium augmented on this wise, doth not attract all the nitre out of the earth it self, but there doth yet some always remain behind: And therefore you need not presently throw it away, but pour thereupon some simple Waters, which after it hath stood thereon for some hours, draw off again, and you shall have a weak Lixivium, which you may try by the proof, and proceed on therewith in the method of augmenting it, and so you will have a continual labour.