# The History of the Royal Society of London/Part 2/Paper 11

THE
HISTORY
Of the Making of
SALT-PETER,
By Mr. Henshaw.
'WHETHER the Nitre of the Antients be of the same species with the Salt which is commonly known by the name of Salt-peter, is variously disputed by very learned Authors amongst the modern Physicians: on the negative side are Mathiolus and Bellonius; the latter of which had the advantage, by the opportunity of his travels in Egypt, to have often seen and handled them both, and is so positive as to pronounce, that in all Christendom there is not one grain of Nitre to be found, unless it be brought from other parts, although at the time of his being in Grand Caire (which was about the year 1550) it was so common there (as he says) that ten pounds of it would not cost a Moidin. Among those that hold the affirmative, the most eminent are Cardan and Longius; and it should seem the general vote of learned Men hath been most favourable to that Opinion, by reason that in all Latin Relations and Prescriptions, the word Nitrum or Halinitrum is most commonly used for Salt-peter.
​'I have often enquired, amongst our London Drugsters, for Egyptian Nitre, and if I had been so fortunate as to have found any, I doubt not but I should have been able to have put an end to that Question by a Demonstration; that is, by turning the greatest part of it into Salt-peter. However, the Observations I have made in my own private Experiments, and in the practice of Salt-peter-men and Refiners of Salt-peter, seem to give me sufficient ground to suspect, that the confidence of those, who hold them to be several Salts, proceedeth chiefly from their being unacquainted with the various Φαινόμενα of Salt-peter in the marking and refining of it: and also their comparing double refined Salt-peter (of which Gunpowder is made) with that description of Nitrum and Aphronitrum in the tenth chapter of the one and thirtieth Book of Pliny's Natural History (the only tolerable account of that Salt that hath been handed to us from Antiquity) where he tells us, That Aphronitrum was Colore pene purpureo, and Egyptian Nitre Fuscum & Lapidosum, adding afterward, Sunt ibi Nitrariæ in quibus rufum exit a colore terræ, which is sufficient to have hinted to any one but moderately versed in the moderate way of ordering Salt-peter, that the Antients were not at all skilled in refining their Nitre from the Earth and common Salt that is usually mingled with it, nor from that foul yellow Oyl, which, it seems, did accompany their Nitre, as well as it doth our Salt-peter, in great abundance; for Pliny takes notice of it, when he mentions the removing the Nitre (after it is grained) out of the Nitrariæ, saying, Hic quoque natura olei intervenit, ad scabiem animalium utilis: And ​indeed this greasy Oyl (which the Workmen call Mother of Salt-peter, and perhaps is but the crude and unripe part of it) doth by nature so wonderfully adhere to every part else of the Peter (it may be ordained for the nutriment and augmentation of it) that the reparation of it, is the sole cause of the great charge and labour that is required to the refining of Peter: otherwise the Peter will be yellow, or brown, or some other dark colour. And Scaliger in his 104. Exercit. sect. 15. saith, Sublustris purpuræ quasi splendor quidem in salis-petræ terris saepenumero est a nobis observatus; and he that shall boil a Lixivium past through a Salt-peter-earth, up to a consistence, without filtring it through ashes, or giving the Salt leave to chrystallize, may perhaps find something not unlike the Nitre of the Antients.
'To make this doubt yet clearer, it will require your patience to observe a few short remains out of the same Pliny, concerning the production of Nitre; saith he, Exigiuum Nitri fit apud Medos, candescentibus siccitate convallibus quod vocant Halmirhaga: minus etiam in Thracia juxta Philippos sordidum Terra quod appellant Agrium.
'This agrees very exactly with what I have been informed by a Refiner of Salt-peter, that near Sophia, Santa Crux, and several other places in Barbary, he hath seen Salt-peter shoot out of the ground (as thick and white as a hoar frost) on many barren and desart Lands; only he adds, that this happens not till the beginning of the rains of August, or September; and that it is the falling of the fresh-water that causes the Salt peter to shoot out into little Chrystals; and that the people of the ​try do no more than take it off the ground as clean as they can, and sell it to Merchant-strangers. This is, says he, the Barbary Peter, which the Refiners buy commonly at twenty shillings per Cent.
'Much after the same manner (by the relation of an Indian Merchant) is that great quantity of Peter produced, which of late years hath been brought into England, and other parts of Christendom, from about Pegu in East-India, saving that the Natives do refine it once, before they sell it to the Merchants: But being not so skilful, to discharge it from the common Salt, which attends Peter, our Workmen do refine it again, before it be fit for Gunpowder.
'The next remark out of Pliny, is, Aquæ vero Nitrose pluribus in locis reperiuntur, sed sine viribus Densandi (he means the heat of the Sun in those places) Optimum Copiosumque in Clytis Macedoniæ quod vocant Cbalastricum candidum purumque proximum sali. Lacus est Nitrosus, exiliente è medio dulci fonticulo, ibi sit Nitrum circa Canis ortum, novenis diebus, totidemque cessat, & rursus innatat & deinde cessat, iis autem diebus quibus gignitur si fuere imbres salsius Nitrum faciunt, Aquilones deterius quia Validius commovent limum. In Egypto autem conficitur multò abundantius sed deterius, nam fuscum lapidosumque est, fit penè eodem modo quo Sal: nisi quod Salinis mare infundunt, Nilum autem Nitrariis.
'How such great plenty of Nitre should be found in the Waters above mention'd, will be no difficulty to conjecture, if we consider that Lakes are the receptacles of Land-floods, and that great Rains may easily bring it to the Lake in Macedonia, from the ​higher parts in the Country about it. And for the River Nile, there must needs be less scruple concerning it, if we call to mind that once in a year, it sweeps with an impetuous overflow the burnt and barren Desarts of Africa under the Torrid Zone; where, by the relation of Travellers, those Sands are visibly full of Nitre, and those few Springs and Wells that are to be found there, are by that reason so bitter, that the Moors and their Camels are forced to make a hard shift with them in their long journeys.
'But when he comes to describe the Aphronitrum, he comes more home, both to the name and nature of our Salt-peter, in these words, Proxima ætas Medicorum tradidit, Aphronitrum in Asia Colligi in speluncis & molibus distillans, dein sole siccant. And Scaliger speaking of Salt-peter, says, Eft quædam Nitri species inhærens Rupibus, in quibus insolatur, ac propterea Salpetra dicitur. And, I my self, for my own satisfaction in the point, have drawn very good Rock-peter out of those Stiriæ, which are usually found hanging like Icycles in arched Cellars and Vaults; and have been told, that a Physician in Shropshire did perform great Cures by vertue of Sal-prunellæ, which he made only of Flower of Brimstone and those Stiriæ.
'But to steer more directly upon our immediate subject Salt-peter; tho' be likely, that the Air is every where full of a volatile kind of Nitre, which is frequently to be seen coagulated into fine white Salt, like Flower of Wheat (but by the very taste may be easily known to be Peter) sticking to the sides of Plaistered-walls, and in Brick-walls to the Mortar between the Bricks, (in dry ​weather, or where the wall is defended from the rain) for Lime doth strongly attract it; though Dew and Rain do conveigh much of it to the Earth, and the Clouds seem to be spread out before the face of the Sun, either to imbibe some part of his influence, or to have a Salt generated in them, for to advance the fertility of the Earth, and certainly they return not without a blessing; for I have more than once extracted Salt-peter out of Rain and Dew, but from the latter more plentifully, and yet even there, is Salt-peter accompanied with a greasy purple Oil, in great plenty: Though (as I have found upon trial) that most standing waters, and even deep wells have some small quantity of Salt-peter in them; though the face of the Earth, if it were not impregnated with this Salt, could not produce Vegetables; for Salt (as the Lord Bacon says) is the first Rudiment of Life; and Nitre is as it were the Life of Vegetables; Yet to be more sure of it, I made Experiment likewise there too, and found some little of it in fallows, and the earth which Moles cast up in the Spring: Though I say the Air and Water want it not, yet it is not there to be had in any proportion, answerable to the charge in getting it: And though the Earth must necessarily have great quantities thereof, generated or infused into it; yet in these temperate Countries of Europe, it is no sooner dilated by Rain water, or the Moisture of the Earth, but it is immediately applied to the production or nutriment of some Plant, Insect, Stone, or Mineral; so that the Artist will find as little of it here to serve his turn, as in the other two Elements.
'The only place, therefore, where Salt-peter is to be found in these Northern Countries, is in Stables, ​Pigeon-houses, Cellars, Barns, Ware-houses, or indeed any place which is covered from the Rain, which would dissolve it, and (as I have said) make it vegetate; as also from the Sun, which doth rarify it, and causeth it to be exhaled into the Air; (For the same reason Husbandmen also might make double or treble the profit they usually do of their Muck, if they will lay it up under a Hovel, or some covered place, until they carry it out upon their Land.) And I have been told by an experienced Workman, that no Earth yields Peter so plentifully, as that in Churches, were it not an impiety to disturb the Allies of our Ancestors, in that sacred Depository.
'Provided always, that the Earth be of good Mould, and the better the Mould is, the more Peter is produc'd; for in Clay, or sandy Earth, little or none is to be found: The freer ingress the Air hath into a place, is still of more advantage, so that the Sun be excluded: And let the Earth be never so good, if it be laid on a brick or boarded floor, it will not be so rich in Peter, as if it have free communication with the Exhalations of the lower parts of the Earth.
'In any place thus qualified, you cannot miss of good quantities of Peter, if it have not been drawn out in some Years before; which a Workman will quickly find, after he hath digged the first spadeful of Earth, by laying a little of it on the end of his tongue, and if it taste bitter, he is sure of good store of mineral, (as they love to call it) that is, Salt-peter; if the Ground be good, it continues rich to six or eight foot deep, and sometimes, but not often, to ten.
​'After the Salt-peter is extracted, if the Earth be laid wet in the same place again, it will be twenty Years e'er any considerable quantity grow there of it; but if the Earth be well dryed, it will come in twelve or fourteen: and if they mingle with the dryed Earth store of Pigeons-dung, and mellow Horse-dung, and then temper it with Urine (as was usual before we were supplyed with Peter from India) it will be fit to dig again in five or six Years. He that shall cast Water upon a Ground fit to dig for Peter, will only sink the Mineral deeper into the Earth; but he that throws Soap-suds on it, will quite destroy the Peter (as the Workmen have a Tradition) and it very well deserves a further Enquiry.
'That Salt-peter, and the way of drawing it out of the Earth, now in use, was a modern Invention, is generally concluded by all Authors; but whether we owe it to chance, or the sagacity of some great Wit, is as unknown, as the time when it was first discovered.
'It seems to have many Years preceeded the Invention of Gun-powder, which by Germans is ascribed to Constantine Autlitzer, or Berthold Schwertz, a Monk of Friburgh, and was, in all probability, not long discovered, when the Inventor (Polydore Virgil tells us) taught the use of Guns to the Venetians, at the Battel of Fossa Claudia, when they obtain'd that notable Victory over the Genoueses, Anno 1380. For there is mention made, both of Salt-peter and Aqua-fortis, in the Writings of Geber, a Spanish Moor, and an Alchymist; but at what time he lived, is unknown, though it be certain, some hundreds of Years before Raimund Lully, who ​about the Year 1333, published some of his Books, wherein he treats of Salt-peter and Aqua-fortis. It is no ill conjecture of Maierus, that the foresaid Monk, being a skilful Alchymist, had a design to draw a higher Spirit from Peter than the common Aqua-fortis; and that he might better open the Body of Peter, he ground it with Sulphur, and Charcoal, by which Composure he soon became the Inventor of Gun-powder.
The Manner of making SALT-PETER.
IN the first place you must be provided of eight or ten Tubs, so large, that they may be able to contain about ten Barrows full of Earth each of them. These Tubs must be all open at the top; but in the bottom of every one of them, you must make a hole near to that side you intend to place outermost, which hole you must fit very well with a Tap and Spigot on the outside downward. On the inside of the Tub, near the Tap-hole, you must carefully place a large wad of straw, and upon that a short piece of board, which is all to keep the earth from stopping up the Tap-hole. When you have placed your Tubs on their stands, at such a distance one from the other, that you may come with ease between them, then fill them up with such Peter-earth as you have chosen for your work, leaving only void about a span's breadth between the earth and the edge of the Tub; then lay on the top of ​the Earth in each Tub, as near as you can to the middle, a rundle of Wicker, like the bottom of a Basket, and about a foot in diameter, and by it stick into the Earth a good strong Cudgel, which must be thrust pretty near the bottom; the Wicker is to keep the Water, when it is poured on, from hollowing and disordering the Earth, and the Cudgel is to be stirred about, to give the Water ingress to the Earth upon occasion: Then pour on your Earth common cold Water, till it stand a hand's breadth over the Earth: When it has flood eight or ten hours, loosen the Spigots, and let the Water rather dribble, than run into half Tubs, which must be set under the Taps: This Lixivium the Workmen call their Raw liquor; and note, that if it come not clear at the first drawing, you must pour it on again, and after some little time draw it off, till it come clear, and of the colour of Urine.
'If you are curious to know how rich your Liquor is before boyling, you may take a Glass-phial, containing a Quart; fill it with the common Water you use, then weigh it exactly; next fill the same Glass with your Liquor, and find the difference of weight, which compared with the quantity of all your Liquors, will give you a very near guess, how much Salt-peter you are like to make by that boyling.
'Then pour on again, on the same Earth, more common Water, that it may bring away what is remaining in the Earth of the former Liquor. This second Liquor is of no other use, but to be poured on new Earth, instead of common Water, because it contains some quantity of Salt-peter in it.
​'When this is done, turn out the useless insipid Earth out of the Tubs, which you must fill with new Earth, and continue this Operation, till you have in the same manner lixiviated all the Earth: Then fill your Copper with your Liquor, which Copper, for one of the Profession, must be about two hundred weight, and set strongly in a Furnace of brick-work; besides, on one side of your Furnace you are to place a Tub full of your Liquor, which at a Tap below may dribble as fast into the Copper, as the force of the Fire doth waste your Liquor, which Invention is only to save charges in Fewel. When you have boyled it up to that height, that a little of it flirted off the finger on a live Charcoal, will flash like Gun-powder (which for the most part falls out to be about two Days and a Nights boiling) at what time, upon tryal, a hundred weight of the Liquor contains about five and thirty pound weight of Peter. But the Workmen seldom make use of any further indication, than by finding the Liquor hang like Oyl on the sides of the brasen Scummer, when 'tis dipped into it, which is a sign it is fit to be passed through the Ashes, which is done in this manner.
'You must prepare two Tubs, fitted after the manner of the first, where you put your Earth, saving that at the bottom of these Tubs, you must lay Reeds or Straw a foot high; over them place loose boards, pretty near one another; over them, a little more Straw (which is to keep the Ashes from the top, and to give the Liquor room to drein the better from them:) Then fill up your Tubs with any sort of Wood-ashes to half a foot of the top; then pour on the foresaid Liquor, as it comes ​ing hot out of the Copper, on the Ashes contained in the first Tub; then after a while draw it off at the top; and so continue putting on and drawing off, first at one Tub of Ashes, then at the other, till your Liquor grow clear, and lose the thick turbid colour it had when it went on.
'When all the Liquor hath in this manner past through the Ashes of both Tubs, that by this means all its greasy oyl is left behind in the Ashes, you must keep it for the second boyling in a Vessel by it self: in the mean time pour upon your Ashes a sufficient quantity of common Water, very hot, once or twice, to bring away what is remaining of the Liquor in the Ashes.
'When you begin the second boyling, put first into the Copper the Water that went last through your Ashes, and as that wasteth, let your strong Liquor drop into the Copper, out of the Tub above described, standing on the side of the Furnace, till the Liquor in the Copper be ready to shoot or chrystalise.
'Note, That toward the end of your boyling, there will arise great store of Scum and Froth; which must be carefully taken off with a great brass Scummer, made like a Ladle, full of little holes, and usually about that time it lets fall some common Salt to the bottom, which you must take up with the said Scummer, and lay it aside for another use.
'To know when the Liquor is ready to shoot into Peter, you need but drop a little of it on a knife, or any other cold thing that hath a smooth superficies, and if it coagulate, like a drop of tallow, and do not fall off the knife when it is turned downward, which also may be judged by its hanging like ​'oyl to the sides of the Scummer. When the Liquor is brought to this pass, every hundred weight of it containeth about threescore and ten pounds weight of Peter.
'When you find your Liquor thus ready to shoot, you must with great Iron Ladles lade it out of the Copper into a high narrow Tub for that purpose, which the Workmen call their settling Tub; and when the Liquor is grown so cold, that you can endure your finger in it, you shall find the common or cubick Salt begin to gravulate and stick to the sides of the Tub; then at the Tap, placed about half a foot from the bottom, draw off your Liquor into deep wooden Trays, or Brass-pans, and the cooler the place is where you let them stand to shoot in, the better and more plentifully will the Salt-peter be produc'd; but it will be of no good colour till it be refined, but will be part white, part yellow, and some part of it blackish.
'The Salt which sticketh to the sides and bottom of the settling Tub is (as I have said) of the nature of common Salt; and there is scarce any Peter to be found but is accompanied with it, though no doubt some of this is drawn out of the Ashes by the second Liquors: If it be foul, they refine it by it self, and about London sell it at good rates to those that salt Neats Tongues, Bacon, and Collar-Beef; for besides a savory taste, it gives a pleasing red colour to most Flesh that is salted with it. Pliny says, Nitrum obsonia alba & deteriora reddit Olera viridiora, whether Salt-peter doth so, I have not yet tryed.
When the Liquor hath stood two Days and two Nights in the Pans, that part of the Liquor which is ​not coagulated, but swims upon the Peter, must be carefully poured off, and being mingled with new Liquors, must again pass the Ashes before it be boiled, else it will grow so greasy it will never generate any Salt.
To Refine
SALT-PETER.
' After you have made your Copper very clean, put in as much Water as you think will dissolve that quantity of Peter you purpose to Refine; when the Water is very hot cast in the Peter by little and little, stirring it about with a Ladle, that it may the sooner dissolve; then increase the Fire till your Liquor begin to boil: In the mean time feel with the Scummer, whether there be at the bottom any Salt undissolv'd, and take it out, for it is Common-Salt, and doth not so soon dissolve as the Peter; then as the Water boils scim off the Froth that swims at the top of it as fast as it riseth; when it hath boiled to the height that a drop of it will coagulate on a Plate (as hath been said above in the making of Salt-peter) then cast in by degrees either a Pint of the strongest Wine-vinegar, or else four Ounces of Allum beaten to powder (some choose burnt Allum) and you shall observe a black Scum to rife on the top of the Liquor, which when you have allowed some time to thicken, you may easily take off with the Scummer; repeat this so often till no more Scum arises. Some do use to throw in a Shovel full of Quick-Lime, and say it makes Peter ​the whiter, and Rock the better; you must take great care all this while the Fire be not too strong, for while this is doing, the Liquor will be apt to boil over, and will not easily be appealed without your great loss.
'When this is done, lade out the Liquor into a settling Tub, and cover it over with a Cloth, that it cool not too soon, and within an hour or two, a thick yellow Fæces will fall to the bottom of the Tub; then quickly draw off the Liquor while it is hot, into the shooting Trays or Pans, and do as you, did in making Peter, saving, that you must cover the Trays with a Cloth, for then the Liquor will begin to shoot at the bottom, which will make the Peter-Rock into much fairer Chrystals, than otherwise it would: When no more Peter will shoot (which is commonly after two days) pour off the Liquor that swims at the top, and put the Peter into a Tub with a hole at the bottom for to drain, and when it is dry, it is fit for use.
'The Figure of the Chrystals is sexangular, and if it hath rightly shot, is fistulous and hollow like a Pipe.
'Before I proceed to tell you, how this darling of Nature (the very Basis and Generation of Nutriment) is converted into Gun-powder (the most fatal Instrument of Death that ever Mankind was trusted withal) I will crave leave to acquaint you with a few Speculations I have of this Salt, which if I could clearly make out, would lead us into the knowledge of many noble Secrets in Nature; as also to a great improvement in the Art of making Salt-peter.
'First then you are to observe, that though Peter go alway in Gun-powder, yet if you fulminate it ​in a Crucible, and burn off the volatile part with Powder of Coal, Brimstone, Antimony or Meal, there will remain a Salt, and yet so fixed (very unlike Common-Salt) that it will endure the force of almost the strongest Fire you can give it; which being dissolved into Water and Spirit of Nitre dropped into it, till it give over hissing (which is the same with the volatile Part that was separated from it in the fulmination) it will be again reduced to Chrystals of Peter as it was at first; which noble Experiment the World hath already been taught by an honourable Member of this Society; with a train of such important Observations, as never before were raised from one Experiment.
'That which I aim at then is, that if the Spirit of the volatile Salt of Soot, or of the Urine, Blood, Horns, Hoofs, Hair, Excrements, or indeed any part of Animals (for all abound with such a volatile Salt fixed, and Oyl as Peter doth) could by the same way, or any like it, be reduc'd to Peter or some Nitrous Salt not much differing from it: It would excellently make out a Theory that I am much delighted with, till I am convinced in it; which is, that the Salt which is found in Vegetables and Animals, is but the Nitre which is so universally diffused through all the Elements (and must therefore make a chief Ingredient in their Nutriment, and by consequence of their Generation) a little altered from its first Complexion: And that the reason why Animals that feed on Vegetables are obliged by Nature to longer meals than those that feed on other Animals, is, because Animals are fuller of that Salt than Vegetables: And indeed such Animals are but Caterers of it for Man; ​and others whom Nature's bounty gratifies with a more lusty and delicious Diet.
'I confess I have been the more confirmed in this fancy, since I have often seen a Friend of mine, with a Natural and Facile Έχειρια convert the greater part of Peter into a Salt so like the Volatile Salt of Urine, that they are scarce to be distinguished by smell or taste, and yet he adds nothing to it that can possibly be suspected to participate of that Nature: But indeed all Volatile Salts are so alike, that it is not easy to distinguish them in any respect.