xxxi. 39 (7), Pliny tells us that salt is found round the edges of

certain lakes in Sicily which are partially dried up in summer by the heat of the sun; while in Phrygia, where much greater evaporation takes place (_ubi largius coquitur_), a lake is dried up (and salt is deposited) to its very middle. _Sal coctus_ was salt recovered from salt water by natural or artificial heat, as distinguished from natural, or rock salt, which was dug out of the ground.[24]

The Arab alchemists before the thirteenth century are as silent as the Greeks: nothing that can be identified with saltpetre is to be found in their voluminous works. The evidence of Geber, so often cited to prove that saltpetre was known to the Arabs in the ninth century, has been stripped of all authority by M. Berthelot, who has satisfactorily proved that there were two Gebers. The real Arab, Jabir, says nothing of saltpetre, but he mentions a salve used by naphtha-throwers[25] as a safeguard against burns. The other Geber, or pseudo-Jabir, was acquainted with saltpetre, as well he might be; for he was a western who lived some time about the year 1300,[26] and wrote a number of Latin works falsely purporting to be translations from the Arabic of the real Jabir. All doubt about the matter has been removed by M. Berthelot’s publication of the real Jabir’s Arabic writings.[27] It has been also suspected that the _sal Indicus_ of the _Liber Sacerdotum, cir._ tenth century,[28] a salt again mentioned in the _Liber Secretorum_ of Bubacar, _cir._ 1000,[29] means saltpetre. Both these works are translations from the Arabic or Persian,[30] and _sal Indicus_ is the literal translation of the Persian—نمك هندي (nimaki Hindi) = نمك سياه (nimaki siyah) = salt of bitumen; a substance of the same family as the “salt of naphtha” also mentioned by Bubacar.

There is no word for saltpetre in classical Sanskrit, _sauverchala_ being a generic term for natural salts, which corresponded to, and was as comprehensive as the _nitrum_, _spuma nitri_, &c., of the West. “Recent Sanskrit formulæ for the preparation of mineral acids containing nitre, mention this salt under the name of _soraka_. This word, however, is not met with in any Sanskrit dictionary, and is evidently Sanskritised from the vernacular _sora_, a term of foreign origin.”[31] Both Professor H. H. Wilson and Professor M. Williams, in their Sanskrit dictionaries, “erroneously render _yavakshara_ as saltpetre, as also does Colebrooke in his ‘Amara-kosha.’”[32] The word means impure carbonate of potash obtained by the incineration of barley straw.[33]

At length, however, notwithstanding coarse scales and clumsy apparatus, the want of all means of registering time and temperature, and the absence of any general principle to guide them in their researches, the alchemists succeeded in differentiating certain natural salts from the rest, and among them saltpetre. The Chinese were acquainted with it about the middle of the thirteenth century.[34] Abd Allah ibn al-Baythar, who died at Damascus in 1248, tells us that the _flower of the stone of Assos_ was called _Chinese snow_ by the Egyptian physicians and _barūd_ (_i.e._ saltpetre) by the (Arab) people of the West.[35] Friar Bacon, whose _De Secretis_ was written before 1249, and Hassan er-Rammah who wrote 1275-95, were thoroughly acquainted with the salt. A grand chemical discovery had been made, and saltpetre became known from China to Spain.

The Egyptians thought fit to call saltpetre “Chinese snow,” but this does not justify the conclusion that the discovery was made by the Chinese. Consider our own phrases “Jerusalem” artichoke, “Welsh” onion, and “Turkey” cock. Jerusalem is a gardener’s corruption of _girasole_, the Turkey came from America, and the home of the Welsh onion is Siberia. The Persians called their native alkaline salt _jamadi Chini_, and no one will suggest that this substance came from China.

It is evident from the way in which it is mentioned by the alchemists of the thirteenth century, and from their primitive methods of refining it, that saltpetre was then in its infancy. Roger Bacon speaks of it as one would speak of a substance recently discovered and still little known—“that salt which is called saltpetre” (_illius salis qui sal petræ vocatur_).[36] Marcus Græcus thought it necessary to explain what the word means, in his 14th recipe which probably belongs to the latter years of the thirteenth century.[37] The methods of refining the salt given by Marcus and Hassan leave no possible doubt that in their time it had but just come into use. It is true that Bacon’s method was much superior, if the solution of his steganogram given in Chap. viii. be accepted. But it would have been past all explanation had the method of the greatest natural philosopher of the age been found to be no better than that of an Arabic druggist or a European fireworker.

As the matter is one of the greatest importance, the methods of all three are given in full, together with that of Whitehorne, 1560. The Waltham Abbey method is added, as a standard by which to judge them. To admit of easy comparison, the corresponding operations are marked with the same letter. The five methods are summed up in Table I.

WALTHAM ABBEY, 1860.

A. _Preparation of grough from natural saltpetre._[38]

Natural saltpetre is dissolved in boiling water, the insoluble impurities removed, and the solution evaporated by the sun or artificial heat. The solid residue is grough saltpetre, and contains 1 to 10 per cent. of impurities, consisting of the chlorides of potassium and sodium, sulphates of potash, soda, and calcium, vegetable matter, sand, and moisture.

B. _Boiling the solution of grough saltpetre._

The grough saltpetre is placed in an open copper with a false bottom; water is added, and heat applied until the mixture boils at 110° C.

C. _Removal of the insoluble impurities._

The scum which rises to the surface during this operation is removed by ladles; the sand and heavy impurities fall upon the false bottom, which is removed just before the mixture boils. The boiling is continued until the scum ceases to rise.

D. _Second boiling of the solution._

Cold water is added; the solution is boiled for a few minutes, and then allowed to cool somewhat.

E. _Filtration._

At 104.5° C. the mother liquid is transferred to a tank with holes in its bottom, closed by filters.

F. _Use of wood-ash, charcoal, &c._

If the impurities prevent the liquid from passing freely through the filters, it is treated with glue, wood-ash, or, better, with a little animal charcoal, which seizes on the impurities and rises to the top as scum.

G. _Crystallisation._

The mother liquid filters into the crystallising trough at 70.2° to 65.8° C.

H. _Stirring the depositing solution._

The solution is kept in constant agitation by poles whilst cooling, in order that it may deposit in minute crystals, called _saltpetre flour_. Large crystals contain more or less of the impure mother liquid.

I. _Washing and drying._

The agitation is discontinued at 25.8° C. and the mother liquid drawn off. The flour is drained on an inclined plane, transferred to a washing vat, where it is washed three times with cold water, and then finally dried.

WHITEHORNE, 1560.

A. _Preparation of grough from natural saltpetre._

On the bottom of a vessel pierced with “three or fower littell holes” is placed a linen cloth, “or else the end of a broom, or some straw.” A layer of nitrified earth, “a spanne thicknesse,” is laid on this, and on the earth “three fingers’ thicknesse” of a mixture of “two parts of unslacked lime and three of oke asshes, or other asshes.... And so, putting one rewe” of saltpetre alternately with one of the mixture, “you shall fill the tubbe ... within a spanne of (its mouth), and the rest you will fill with water.” The water, on percolating through the mass, drips into a brass cauldron which, when two-thirds full, is boiled “till it come to one-third part or thereabouts. And after take it off and put it to settell in a great vessell,” when it is to be “clarified and from earthe and grosse matter diligentlie purged.”

B. _Boiling the solution of grough saltpetre._

The solution is then “taken and boyled of new.”

F. _Use of wood-ash, animal charcoal, &c._

When the solution boils and throws up scum, it is treated with a mixture of “3 parts of oke asshes and 1 of lime, together with 4 lbs. of rock alum to every 100 lbs. of the mother liquid.” “In a little time you shall see it alaie, both clear and fair and of an azure colour.”

C. _Removal of insoluble impurities._

The heavy impurities, which sink to the bottom, are got rid of by pouring the clarified mother liquid into another vessel.

G. _Crystallisation._

“Take it out and put it in vessels of woode or of earth that are rough within, with certain sticks of wood, to congeal.”

I. _Washing and drying._

“This same saltpeter being taken from the sides of the vessel where it congealed, and in the water thereof washed, you must lay it upon a table to drie throughly.”

F´.[39] _Use of wood-ash, animal charcoal, &c._

“Minding to have (saltpetre) above the common use, for some purpose, more purified, &c. (which for to make exceeding fine powder, or aqua fortis, is most requisite so to be):—take of the aforesaid mixture (F) ... and for every barrel of water you have put in the cauldron ... you must put into it five potfulls” of the mixture. “In the same quantity of water so prepared, put so much saltpeter as it will dissolve.”

D. _Second boiling of the solution._

Boil the whole until it “resolve very well.”

E. _Filtration._

When the scum rises, transfer the mother liquid to a tub with holes in the bottom, on which is laid a linen cloth covered with a layer of sand four finger-breadths deep.

D´. _Third boiling of the solution._

The filtered liquid is boiled again “in order to make the greater part of the water seeth away.... Make it boil so much until you see it ready to thicken, pouring in now and then a little of the mixture” (F).

G´. _Final crystallisation._

The mother liquid is then transferred to wooden troughs “to congeal,” for which three or four days are allowed. “After this sort thou shalt make the saltpeter most white and fair, and much better than at the first setting.”

“LIBER IGNIUM,” _cir._ 1300.

A. _Preparation of grough from natural saltpetre._

If natural saltpetre is dissolved in boiling water, cleansed, and passed through a filter, and boiled for a day and a night; the (grough) saltpetre will be found deposited in crystals at the bottom of the vessel.

The original is as follows:—

“Nota, quod sal petrosum est minera terræ et reperitur in scrophulis contra lapides. Hæc terra dissolvitur in aqua bulliente, postea depurata et distillata per filtrum et permittatur per diem et noctem integram decoqui, et invenies in fundo laminas salis conielatas cristallinas.”[40]

HASSAN ER-RAMMAH, 1275-95.

A. _Preparation of grough from natural saltpetre._

“Take white, clean, bright (natural) saltpetre _ad lib._, and two new (earthen) jars. Put the saltpetre into one of them, and add some water. Put the jar on a gentle fire until it gets warm” (and the saltpetre dissolves. Skim off) “the scum that rises” (and) “throw it away. Stir up the fire until the liquid becomes quite clear. Then pour it into the other jar in such a way that no scum remains attached to it. Place this jar on a low fire until the contents begin to coagulate. Then take it off the fire, and beat (the crystals) gently.”

F. _Use of wood-ash, animal charcoal, &c._

“Take dry willow wood, burn it, and plunge it into water according to the recipe for its incineration. Take three parts by weight of the saltpetre” (just obtained), “and the third of a part of the wood-ash, which has been carefully pulverised, and put the mixture into a jar—if made of brass, so much the better.”

B. _Boiling the solution of grough saltpetre._

“Add water and apply heat, until the ashes and saltpetre no longer adhere together. Beware of sparks.”

The original is as follows:—[41]

باب صثة حل البارود يوخذ البارود الابيض النقى النارى مهما اردت وتاخذ طاجنين جدد ويحط فى الطاجن الواحد ويغمر بالماء ويوقد عليه نار لينة حتى يفتر وتطلع رغوته فارمها واوقد تحته جيدا حتى يروق ماؤه الى غاية ويقلب الماء الرايق قى طاجن اخر بحيث لا يتراك من التفل شى ويوخذ عليه وقدا لطيفا الى ان يجمد وتشيله وتصحنه ناعما ويوخذ الحطب الصفصاف اليابس يحرق ويغمر على صفة الحراق ويزن من البارود الثلثين والثلث من رماد الفحع الذى صحنته بالميزان ويعاد الى الطاجنين وان كانت الاعادة فى طاجن نحاس فهو اجود ويعمل عليه قليل ماء وتحمصه بحيث ان لا يلتزق واحذو من شرر النار

ROGER BACON, _cir._ 1248.

A. _Preparation of grough from natural saltpetre._

Carefully wash the natural saltpetre, and (as far as possible) remove all impurities. Dissolve it in water over a gentle fire, and boil it until the scum ceases to rise, and it is purified and clarified. Let the operation be repeated again and again, until the solution is clear and bright. Let it then deposit its crystals of the stone which is not a stone,[42] and dry them in a warm place.

B. _Boiling the solution of grough saltpetre._

Pulverise the crystals of grough saltpetre thus obtained, and immerse them in water. Make a powder of two purifying substances in the proportion of 3:2. Dissolve the crystals over a gentle fire.

F. _Use of wood-ash, charcoal, &c._

To the powder add some animal charcoal, and thoroughly incorporate the ingredients (in a vessel). Then pour the hot solution upon it, and your object (of clarifying the mother liquid) will be gained.

C. _Removal of the insoluble impurities._

If (by its appearance and taste you judge that) the solution is good, pour it out (into a crystallising vessel, leaving the heavy impurities behind).

G. _Crystallisation._

(The mother liquid is now allowed to crystallise.)

H. _Stirring the depositing solution._

(While depositing), stir the solution with a pestle. Collect the crystals as best you can, and gradually draw off the mother liquid.

The original is as follows:—

Calcem diligenter purifica, ut fiat terra pura penitus liberata ab aliis elementis. Dissolvatur in aqua cum igne levi, ut decoquatur quatenus separetur pinguedo sua, donec purgatur et dealbetur. Iteretur distillatio donec rectificetur: rectificationis novissima signa sunt candor et crystallina serenitas. Ex hac aqua materia congelatur. Lapis vero Aristotelis, qui non est lapis, ponitur in pyramide in loco calido.

Accipe lapidem et calcina ipsum. In fine parum commisce de aqua dulci; et medicinam laxativam compone de duabus rebus quarum proportio melior est in sesquialtera proportione. Resolve ad ignem et mollius calefac. Mixto ex Phœnice adjunge, et incorpora per fortem motum; cui si liquor calidus adhibeatur, habebis propositum ultimum. Evacuato quod bonum est. Regyra cum pistillo, et congrega materiam ut potes, et aquam separa paulatim.[43]

TABLE I.

_Methods of Refining Saltpetre._

+---------------------------+---+---+---+---+---+---+----+---+---+----+----+ | Roger Bacon, _cir._ 1248 | A | B | F | C | G | H |... |...|...|... |... | | Hassan er-Rammah, | | | | | | | | | | | | | 1275-95 | A | F | B |...|...|...|... |...|...|... |... | | Liber Ignium, _cir._ 1300 | A |...|...|...|...|...|... |...|...|... |... | | Whitehorne, 1560 | A | B | F | C | G | I | F´ | D | E | D´ | G´ | | Waltham Abbey, 1860. | A | B | C | D | E | F | G | H | I |... |... | +---------------------------+---+---+---+---+---+---+----+---+---+----+----+

A = Preparation of grough from natural saltpetre. B = Boiling the solution of grough saltpetre. C = Removal of insoluble impurities. D = Second boiling of the solution. E = Filtration. F = Use of wood-ash, animal charcoal, &c. G = Crystallisation. H = Stirring the depositing solution. I = Washing and drying.

The simple and highly probable conclusion to be drawn from the foregoing facts is, that saltpetre was not discovered until the second quarter of the thirteenth century; but this conclusion is not universally accepted. It is said by some that although saltpetre was unknown to the rest of the world until then, it had been secretly used by the Greeks for five hundred years. This theory will be examined in the following chapter.