Chap. II Of the Nitrous Acid
Process I.
To extract Nitre out of nitrous Earths and Stones. The Purification of Salt-petre. Mother of Nitre. Magnesia.
Take any quantity of nitrous earths or stones; reduce them to powder; and therewith mix a third part of the ashes of green-wood and quick-lime. Put this mixture into a barrel or vat, and pour on it hot water to about twice the weight of the whole mass. Let it stand thus for twenty-four hours, stirring it from time to time with a stick. Then filter the liquor through brown paper, or pass it through a flannel bag, till it come clear: it will then have a yellowish colour. Boil this liquor, and evaporate till you perceive that a drop of it let fall on any cold body coagulates. Then stop the evaporation, and set your liquor in a cool place. In the space of four and twenty hours crystals will be formed in it, the figure of which is that of an hexagonal prism, having its opposite planes generally equal, and terminated at each extremity by a pyramid of the same number of sides. These crystals will be of a brownish colour, and deflagrate on a live coal.
Decant the liquor from these crystals; mix it with twice its weight of hot water; evaporate and crystallize as before. Repeat the same operation till the liquor will yield no more crystals: it will then be very thick, and goes by the name of Mother of Nitre.
OBSERVATIONS.
Earths and stones that have been impregnated with animal or vegetable juices susceptible of putrefaction, and have been long exposed to the air, but sheltered from the sun and rain, are those which yield the greatest quantity of Nitre. But all sorts of earths and stones are not equally fit to produce it. None is ever found in flints or sands of a crystalline nature.
Some earths and stones abound so with Nitre, that it effloresces spontaneously on their surface, in the form of a crystalline down. This Nitre may be collected with brooms, and accordingly has the name of Salt-petre Sweepings. Some of this sort is brought from India.
Hitherto we are much in the dark as to the origin and generation of Nitre. Some Chymists pretend that the Nitrous Acid is diffused through the air, and gradually deposited in such earths and stones as are qualified to receive it.
Others, considering that none of it is ever obtained but from earths that have been impregnated with vegetable or animal juices, have from thence concluded those two kingdoms to be the general repositories of the Nitrous Acid; that if we do not perceive it to exist in such matters at all, or at least in any great quantity, till they have undergone putrefaction, and are in some measure incorporated with suitable earths and stones, it is because the Acid is so entangled with heterogeneous particles that it requires the assistance of putrefaction, and much more of filtration through an earth, to disengage it, and enable it to appear in its proper nature.
Lastly, others are of opinion that this Acid is no other than the universal or Vitriolic Acid; disguised indeed by a portion of the Phlogiston, which is combined with it in a peculiar manner by the means of putrefaction. They ground this opinion chiefly on the analogy or resemblance which they find between the Nitrous Acid and the Volatile Sulphureous Spirit. Its volatility, its pungent smell, its properties of taking fire, and of destroying the blue and violet colours of vegetables, serve them as so many proofs.
Their opinion is the more probable on this account, that even though the Nitrous Acid should actually be produced by vegetable and animal substances, yet as these substances themselves draw all their component principles from the earth, and as the Vitriolic Acid is diffused through all the soils which afford them nourishment, there is great reason to think that the Nitrous Acid is no other than the Vitriolic Acid altered by the changes and combinations it hath undergone in its passage into and through those substances. In 1750 the Royal Academy of Sciences at Berlin proposed an account of the generation of Nitre as the subject for their prize, which was conferred on a Memoir wherein this last opinion was supported by some new and very judicious experiments.
The process by which our Salt-petre makers extract Nitre in quantities, out of rubbish and nitrous earths, is very nearly the same with that here set down; so that I shall not enter into a particular account of it. I shall only take notice of one thing, which it is of some consequence to know; namely, that there is no nitrous earth which does not contain sea-salt also. The greatest quantities of this salt are to be found in those earths which have been drenched with urine, or other animal excrements. Now as the rubbish of old houses in great cities is in this class, it comes to pass that when the Salt-petre workers evaporate a nitrous lixivium drawn from that rubbish, as soon as the evaporation is brought to a certain pitch, a great many little crystals of sea-salt form in the liquor, and fall to the bottom of the vessel.
The Salt-petre workers in France call these saline particles the Grain, and take care to separate them from the liquor (which, as long as it continues hot, keeps the salt-petre dissolved) before they set it to crystallize. This fact seems a little singular, considering that sea-salt dissolves in water more easily than salt-petre, and crystallizes with more difficulty.
In order to discover the cause of this phenomenon, we must recollect some truths delivered in our theoretical Elements. The first is, that water can keep but a determinate quantity of any salt in solution, and that if water fully saturated with a salt be evaporated, a quantity of salt will crystallize in proportion to the quantity of water evaporated. The second is, that those salts which are the most soluble in water, particularly those which run in the air, will dissolve in cold and in boiling water equally; whereas much greater quantities of the other salts will dissolve in hot and boiling water than in cold water. These things being admitted, when we know that sea-salt is one of the first sort, and salt-petre of the second, the reason why sea-salt precipitates in the preparation of salt-petre appears at once. For,
When the solution of Salt-petre and Sea-salt comes to be evaporated to such a degree that it contains as much Sea-salt as it possibly can, this salt must begin to crystallize, and continue to do so gradually as the evaporation advances. But because at the same time it does not contain as much salt-petre as it can hold, seeing it is capable of dissolving a much greater quantity thereof when it is boiling hot than when it is cold, this last-named salt will not crystallize so soon. If the evaporation were continued till the case of the Salt-petre came to be the same with that of the Sea-salt, then the salt-petre also would begin to crystallize gradually in proportion to the water evaporated, and the two salts will continue crystallizing promiscuously together: but it is never carried so far; nor is it ever necessary: for, as the water cools, it becomes more and more incapable of holding in solution the same quantity of salt-petre as when it was boiling hot.
And then comes the very reverse, with regard to the crystallizing of the two salts; for then the Salt-petre shoots, and not the Sea-salt. The reason of this fact also is founded on what has just been said. The Sea-salt, of which cold water will dissolve as much as boiling water, and which owed its crystallizing before only to the evaporation, now ceases to crystallize as soon as the evaporation ceases; while the Salt-petre, which the water kept dissolved only because it was boiling hot, is forced to crystallize merely by the cooling of the water.
When the solution of Salt-petre has yielded as many crystals of that Salt as it can yield by cooling, it is again evaporated, and being then suffered to cool yields more crystals. And thus they continue evaporating and crystallizing, till the liquor will afford no more crystals. It is plain that as the Salt-petre crystallizes, the proportion of Sea-salt to the dissolving liquor increases; and as a certain quantity of water evaporates also during the time employed in crystallizing the Salt-petre, a quantity of Sea-salt, proportioned to the water so evaporating, must crystallize in that time: and this is the reason why Salt-petre is adulterated with a mixture of Sea-salt. It likewise follows that the last crystals of Nitre, obtained from a solution of Salt-petre and Sea-salt, contain much more Sea-salt than the first.
From all that has been said concerning the crystallization of Salt-petre and Sea-salt, it is easy to deduce the proper way of purifying the former of these two Salts from a mixture of the latter. For this purpose the Salt-petre to be refined need only be dissolved in fair water. The proportion between the two salts in this second solution is very different from what it was in the former; for it contains no more Sea-salt than what had crystallized along with the Salt-petre under favour of the evaporation, the rest having been left dissolved in the liquor that refused to yield any more nitrous crystals.
As there is therefore a much greater quantity of Salt-petre than of Sea-salt in this second solution, it is easy to evaporate it to such a degree that a great deal of Salt-petre shall crystallize, while much more of the water must necessarily be evaporated before any of the Sea-salt will crystallize.
However, the Salt-petre is not yet entirely freed from all mixture of Sea-salt by this first purification; for the crystals obtained from this liquor, in which Sea-salt is dissolved, are still encrusted, and, as it were, infected therewith: hence it comes, that, to refine the Salt-petre thoroughly, these crystallizations must be repeated four or five times.
The Salt-petre men commonly content themselves with crystallizing it thrice, and call the produce Salt-petre of the first, second, or third shoot, according to the number of crystallizations it has undergone. But their best refined Salt-petre, even that of the third shooting, is not yet sufficiently pure for Chymical experiments that require much accuracy: so that it must be further purified; but still by the same method.
The Nitrous Acid is not pure in the earths and stones from which it is extracted. It is combined partly with the very earth in which it is formed, and partly with the Volatile Alkali produced by the putrefaction of the vegetable or animal matters that concurred to its generation. A Fixed Alkali and Quick-lime are added to the lixivium of a nitrous earth, in order to decompose the nitrous Salt formed in that earth, and to separate the Acid from the Volatile Alkali and the absorbent earth with which it is united: thence comes that copious sediment which appears in the lye at the beginning of the evaporation. These matters form with that Acid a true Nitre, much more capable than the original Nitrous Salts of crystallization, detonation, and the other properties which are essential thereto. The basis of Nitre is therefore a Fixed Alkali mixed with a little lime.
The Mother of Nitre, which will yield no more crystals, is brown and thick: by evaporation over a fire it is further inspissated, and becomes a dry, solid body; which, however, being left to itself soon gives, and runs into a liquor. This water still contains a good deal of Nitre, Sea-salt, and the Acids of these Salts united with an absorbent earth. It contains moreover a great deal of a fat, viscid matter, which prevents its crystallizing.
All saline solutions in general, after having yielded a certain quantity of crystals, grow thick, and refuse to part with any more, though they still contain much Salt. They are all called Mother-waters, as well as that which hath yielded Nitre. The Mother-waters of different Salts may prove the subjects of curious and useful inquiries.
If a Fixed Alkali be mixed with the Mother of Nitre, a copious white precipitate immediately falls, which being collected and dried is called Magnesia. This precipitate is nothing but the absorbent earth that was united with the Nitrous Acid, together with a good deal of the lime that was added, and was also united with that Acid, from which they are now separated by the Fixed Alkali, according to the usual laws of affinities.
The Vitriolic Acid poured upon Mother of Nitre causes many Acid vapours to rise, which are a compound of the Nitrous and Marine Acids, that is, an Aqua Regia. On this occasion also there falls a large quantity of a white powder, which is still called Magnesia; yet it differs from the former in that it is not, like it, a pure absorbent earth, but combined with the Vitriolic Acid.
An Aqua regis may also be drawn from nitrous earths by the force of fire only, without the help of any additament.
Process II
To decompose Nitre by means of the Phlogiston. Nitre fixed by Charcoal. Clyssus of Nitre. Sal Polychrestum.
Take the purest Salt-petre in powder; put it into a large crucible, which it may but half fill; set the crucible in a common furnace, and surround it with coals. When it is red-hot the Nitre will melt, and become as fluid as water. Then throw into the crucible a small quantity of charcoal-dust: the Nitre and the Charcoal will immediately deflagrate with violence; and a great commotion will be raised, accompanied with a considerable hissing, and abundance of black smoke. As the charcoal wastes, the detonation will abate, and cease entirely as soon as the coal is quite consumed.
Then throw into the crucible the same quantity of charcoal-dust as before, and the same phenomena will be repeated. Let this coal also be consumed: then add more, and go on in the same manner till you can excite no further deflagration; always observing to let the burning coal be entirely consumed before you add any fresh. When no deflagration ensues, the matter contained in the crucible will have lost much of its fluidity.
OBSERVATIONS.
Nitre will not take fire, unless the inflammable matter added to it be actually burning, or the Nitre itself red-hot, and so thoroughly ignited, as immediately to kindle it. Therefore, if you would procure the detonation of Nitre with charcoal, and make use of cold charcoal, as in the process, the Nitre in the crucible must be red-hot, and in perfect fusion: but you may also use live coals, and then the Nitre need not be red-hot.
It is proper that the crucible used in this experiment should be only half full; for during the detonation its contents swell, and might run over without this precaution. For the same reason the charcoal-dust is to be thrown in by little and little; and that first put in must be entirely consumed before any fresh be added.
The matter remaining in the crucible after the operation is a very strong Fixed Alkali. Being exposed to the air it quickly attracts the moisture thereof, and runs into a liquor. It is called Alkalizated Nitre, or, to distinguish it from Nitre alkalizated by other inflammable matters, Nitre fixed by charcoal.
However, this Alkali is not absolutely pure. It still contains a portion of the Nitre that hath not been decomposed. For when there remains but a little of this salt mixed with a great quantity of Alkali, which is not inflammable, the Alkali in some measure shelters it, coats it over, and obstructs that immediate contact with the inflammable matters applied, which is necessary to make it deflagrate.
If the Fixed Alkali be desired perfectly free from any mixture of undecomposed Nitre, the fire about the crucible must be considerably increased as soon as the detonation is entirely over; the matter must be made to flow, which requires a much stronger heat than would melt Nitre, and kept thus in fusion for about an hour. After this no perfect Nitre will be found therein: for the little that was left, being unable to abide the force of the fire, as not being extremely fixed, either is entirely dissipated, or loses its Acid, which is carried off by the violence of the heat.
Fixed Nitre contains also a portion of the earth that constituted the basis of the Nitre, which is no other than the lime employed in its crystallization, or else some of the earth with which its Acid was originally combined, and which it retained in crystallizing. When Nitre is deflagrated with such matters as produce ashes, these ashes likewise furnish a certain quantity of earth, which mixes with the Fixed Alkali. To separate these several earths from the Alkali, nothing more is requisite than to let it run per deliquium, or to dissolve it in water, and filter the solution through brown paper. Whatever is saline will pass through the filtre with the water, and the earthy part will be left upon it.
The Nitrous Acid is not only dissipated during the deflagration of the Nitre, but is even destroyed, and perfectly decomposed. The smoke that rises during the operation has not the least odour of an Acid. Its nature may be accurately examined by catching it in proper vessels, and condensing it into a liquor.
Nitre differs from Sulphur, and from all other inflammable bodies whatever, in this, that the free access of the air is indispensably necessary to make any of the others burn; whereas Nitre, and Nitre only, is capable of burning in close vessels: and this property furnishes us with the means of collecting the vapours which it discharges in deflagration.
For this purpose, to a tubulated earthen retort you must fit two or three large adopters: set the retort in a furnace; and under it make a fire sufficient to keep its bottom moderately red. Then take a small quantity, two or three pinches for example, of a mixture of three parts of Nitre with one of charcoal-dust, and drop it into the retort through its tube, which must be uppermost, and immediately stopped close. A detonation instantly ensues, and the vapours that rise from the inflamed mixture of Nitre and charcoal, passing out through the neck of the retort into the adopters, circulate therein for a while, and at last condense into a liquor.
When the detonation is over, and the vapours condensed, or nearly so, drop into the retort another equal quantity of the mixture; and repeat this till you find there is liquor enough in the recipients to be examined with ease and accuracy. This liquor is almost insipid, and shews no tokens of acidity; or at most but very slight ones. It is called Clyssus of Nitre.
It is easy to perceive why several adopters are required in this experiment, and why a very small quantity of the mixture must be introduced into the retort at once. The explosion, and the quantity of air and vapours discharged on this occasion, would quickly burst the vessels, if all these precautions were not attended to. This plainly appears from the terrible effects of gun-powder, which is nothing but a composition of Nitre, Sulphur, and Charcoal.
Nitre is also decomposed and takes fire by the means of Sulphur; but the circumstances and the result differ widely from those produced therewith by charcoal, or any other inflammable body.
Nitre deflagrates with Sulphur on account of the Phlogiston which the latter contains. If one part of Sulphur be mixed with two or three parts of Nitre, and the mixture thrown by little and little into a red-hot crucible, upon every projection there arises a detonation accompanied with a vivid flame.
The vapours discharged on this occasion have the mingled smell of a Sulphureous Spirit and Spirit of Nitre; and if they be collected by means of a tubulated retort, and such an apparatus of vessels as was used in the preceding experiment, the liquor contained in the recipients is found to be an actual mixture of the Acid of Sulphur, the Sulphureous Spirit, and the Acid of Nitre; the first being in greater quantity than the other two, and the second greater than the last.
Nor is the remainder after detonation a Fixed Alkali, as in the former experiments; but a Neutral Salt, consisting of the Acid of Sulphur combined with the Alkali of Nitre; a sort of Vitriolated Tartar known in medicine by the name of Sal Polychrestum.
There are evidently two essential differences between this last experiment and the preceding one. What remains after the deflagration of Nitre with Sulphur is not a Fixed Alkali: and, moreover, the vapours emitted in the operation are impregnated with a quantity of the Nitrous Acid; which is not the case when Nitre is decomposed by any other inflammable matter which contains no Vitriolic Acid.
The reason of these differences is naturally deducible from what hath been already said concerning the properties of the Vitriolic and Nitrous Acids. We have seen that by burning Sulphur its Acid is not decomposed, but only separated from its Phlogiston. We also know, that its Acid has a great affinity with Fixed Alkalis. These things being granted, it follows that, as soon as the Nitrous Acid quits its Alkaline basis, by deflagrating with the Phlogiston of the Sulphur, the Acid of this very Sulphur, being set at liberty by that deflagration, must unite with the Alkaline basis deserted by the Acid of Nitre, and therewith form a Neutral Salt. Hence, instead of a Fixed Alkali, we find at the end of the operation a sort of Vitriolated Tartar; the Acids of Sulphur and of Vitriol being the same, as is evident from what hath been above said concerning them.
In order to discover the cause of the other phenomenon, we must recollect two things advanced in our Elements of the Theory; to wit, that the affinity of the Vitriolic Acid with Fixed Alkalis is greater than that of the Nitrous Acid; and again, that the Nitrous Acid is not capable of combining and taking fire with the Phlogiston, but when it is in the form of a Neutral Salt, that is, when it is united with some alkaline, earthy, or metallic basis. If these two principles be applied to the effect in question, the solution is easy and natural. For, in the deflagration of Nitre with Sulphur, the Phlogiston is not the only substance capable of separating the Nitrous Acid from its basis: the Acid of the Sulphur, more and more of which is set at liberty as the Phlogiston is consumed, is also capable of producing the same effect; but with this difference, that the portion of the Nitrous Acid which is detached from its Alkali by the Phlogiston is at the same instant set on fire and decomposed by that union; whereas the portion thereof which is separated by the Vitriolic Acid, being when so separated incapable of uniting with the Phlogiston, and of consuming therewith, is preserved entire, and rises in vapours, together with that portion of the Vitriolic Acid which could not unite with the basis of the Nitre.
Process III
To decompose Nitre by means of the Vitriolic Acid. The Smoking Spirit of Nitre. Sal de duobus. The Purification of Spirit of Nitre.
Take equal parts of well purified Nitre and Green Vitriol: dry the Nitre thoroughly, and bruise it to a fine powder. Calcine the Vitriol to redness: reduce it likewise to a very fine powder; and mingle these two substances well together. Put the mixture into an earthen long-neck, or a good glass retort coated, of such a size that it may be but half full.
Set this vessel in a reverberating furnace covered with its dome; apply a large glass receiver, having a small hole in its body, stopped with a little lute. Let this receiver be accurately luted to the retort with the fat lute, and the joint covered with a slip of canvas smeared with lute made of quick-lime and the white of an egg. Heat the vessels very gradually. The receiver will soon be filled with very dense red vapours, and drops will begin to distil from the nose of the retort.
Continue the distillation, increasing the fire a little when you observe the drops to follow each other but slowly, so that above two thirds of a minute passes between them; and, in order to let out the redundant vapours, open the small hole in the receiver from time to time. Towards the end of the operation raise the fire so as to make the retort red. When you find that, even when the retort is red-hot, nothing more comes over, unlute the receiver, and without delay pour the liquor it contains into a crystal bottle, and close it with a crystal stopple ground in its neck with emery. This liquor will be of a reddish yellow colour, smoking exceedingly, and the bottle containing it will be constantly filled with red fumes like those observed in the receiver.
OBSERVATIONS.
The Vitriolic Acid having a greater affinity with Fixed Alkalis than with any other substance, the Phlogiston excepted, and being in the Vitriol united with a ferruginous basis, will naturally quit that basis to join with the Fixed Alkali of the Nitre; the Acid whereof being weaker than the Vitriolic, as we have already observed on several occasions, must needs be thereby expelled from its basis. The Nitre therefore is decomposed by the Vitriol, and its Acid being set at liberty, is carried up by the force of the fire.
Indeed the Nitrous Acid, being thus separated from its alkaline basis, might be expected to combine with the ferruginous basis of the Vitriol: but as it has, like all other Acids, much less affinity with Metallic substances than with Alkalis, even a moderate degree of fire is sufficient to separate it from them. Moreover, this Acid hath either no effect, or very little, upon iron that has lost much of its Phlogiston by contracting an union with any Acid; which is the case of the ferruginous basis of Vitriol.
By the process here delivered a very strong, perfectly dephlegmated, and vastly smoking Spirit of Nitre is obtained. If the precautions of drying the Nitre and calcining the Vitriol be neglected, the Acid that comes over, greedily attracting the water contained in these salts, will be very aqueous, will not smoke, and will be almost colourless, with a very slight tinge of lemon.
The fumes of highly concentrated Spirit of Nitre, such as that obtained by the above process, are light, corrosive, and very dangerous to the lungs; being no other than the most dephlegmated part of the Nitrous Acid. The person therefore who unlutes the vessels, or pours the liquor out of the receiver into the bottle, ought with the greatest caution to avoid drawing them in with his breath; and for that reason ought to place himself so that a current of air, either natural or artificial, may carry them off another way. It is also necessary that care be taken, during the operation, to give the vapours a little vent every now and then, by opening the small hole in the recipient; for they are so elastic, that, if too closely confined, they will burst the vessels.
When the operation is over, you will find a red mass at the bottom of the retort, cast, as it were, in a mould. This is a Neutral Salt of the nature of Vitriolated Tartar, resulting from the union of the Acid of the Vitriol with the Alkaline basis of the Nitre.
The ferruginous basis of the Vitriol, which is mixed with this salt, gives it the red colour. To separate it therefrom, you must pulverise it, dissolve it in boiling water, and filter the solution several times through brown paper; because the ferruginous earth of the Vitriol is so fine, that some of it will pass through the first time. When the solution is very clear, and deposites no sediment, let it be set to shoot, and it will yield crystals of Vitriolated Tartar; to which Chymists have given the peculiar title of Sal de duobus.
In this Caput mortuum we frequently find, besides the ferruginous earth of Vitriol, a portion of Nitre and Vitriol not decomposed; either because the two salts were not thoroughly mingled, or because the fire was not raised high enough towards the end of the operation.
Nitre may also be decomposed, and its acid obtained, by the interposition of any of the other Vitriols, Alums, Gypsums, Boles, Clays; in short, by means of any compound in which the Vitriolic Acid is found, provided it have not a Fixed Alkali for its basis.
The distillers of Aqua fortis, who make large quantities at a time, and who use the least chargeable methods, do their business by the means of earths impregnated with the Vitriolic Acid; such as Clays and Boles. With these earths they accurately mix the Nitre from which they intend to draw their Spirit: this mixture they put into large oblong earthen pots, having a very short curved neck, which enters a recipient of the same matter and form. These vessels they place in two rows opposite to each other in long furnaces, and cover them over with bricks cemented with Windsor-loam, which serves for a reverberatory: then they light the fire in the furnace, making it at first very small, only to warm the vessels; after which they throw in wood, and raise the fire till the pots grow quite red-hot, in which degree they keep it up till the distillation is entirely finished.
The Acid of Nitre may also be separated from its basis by means of the pure Vitriolic Acid. For this purpose the Nitre from which you mean to extract the Acid must be finely pulverized, put into a glass retort, and a third of its weight of concentrated Oil of Vitriol poured on it: the retort must be placed in a reverberating furnace, and a receiver, like that used in the preceding operation, expeditiously applied.
As soon as the Oil of Vitriol touches the Nitre the mixture grows hot, and copious red fumes begin to appear: some drops of the Acid come over even before the fire is kindled in the furnace.
On this occasion the fire must be moderate; because the Vitriolic Acid, being clogged by no basis, acts upon the Nitre much more briskly, and with much greater effect, than when it is not pure.
This operation may be performed by a sand-heat; which is a speedy and commodious way of obtaining the Nitrous Acid. In other respects the precautions recommended in the preceding experiment must be carefully observed here, both in distilling the Acid and in taking it out of the receiver.
The Spirit of Nitre extracted by this method is as strong, and smokes as much, as that obtained by calcined Vitriol, provided the Oil of Vitriol made use of be well concentrated; but it is generally tainted by the admixture of a small portion of the Vitriolic Acid, which, having no basis of its own to restrain it, is carried up by the heat before it can lay hold of the basis of the Nitre.
There are several experiments in Chymistry that succeed equally well whether the Nitrous Acid be or be not thus adulterated with a mixture of the Vitriolic Acid; but there are some, as we shall see, that will not succeed without a Spirit of Nitre so mixed. If the Acid be distilled with a view to such experiments, it must be kept as it is. But most experiments require the Spirit of Nitre to be absolutely pure; and if it be intended for such, it must be perfectly cleansed from the Vitriolic taint.
This is easily effected by mixing your Spirit with very pure Nitre, and distilling it a second time. The Vitriolic Acid, with which this Spirit of Nitre is adulterated, coming in contact with a great quantity of undecomposed Nitre, unites with its Alkaline basis, and expels a proportionable quantity of the Nitrous Acid.
In the retort made use of to distil the Nitrous Acid, by means of the pure Vitriolic Acid, is found a Caput mortuum, differing from that left after the distillation of the same Acid by the interposition of Vitriol, in as much as it contains no red ferruginous earth. This is a very white saline mass, moulded in the bottom of the retort: if you pound it, dissolve it in boiling water, and evaporate the solution, it will shoot into crystals of Vitriolated Tartar: sometimes also it contains a portion of undecomposed Nitre, which shoots after the Vitriolated Tartar, because it is much more soluble in water.