In examining the question, whether Theophrastus, Pliny, and in general
the ancient Greeks and Romans, were acquainted with our saltpetre, or
at what period it became known, I shall perhaps meet with as little
success as those who have preceded me in the same research[1190]. I
shall therefore be satisfied if competent judges allow that I have
contributed anything new that can tend to illustrate the subject.
Our saltpetre, which is commonly called _nitrum_, and sometimes, though
more rarely, _sal nitræ_, is a neutral salt composed of a peculiar
acid, named the acid of saltpetre or nitric acid, and that alkali
called potash. The characters by which it is most readily distinguished
from other salts are its cooling taste, its fusibility when exposed to
a small degree of heat, and in particular its so-called deflagration;
that is, the property it has when placed in the fire, or on an ignited
body, or when melted in a crucible, with a combustible substance, of
suddenly bursting into a very bright flame, by which it loses its acid,
and nothing remains but a carbonate of potash. The principal use of
it is in making gunpowder, and for the preparation of that acid known
under the name of aquafortis[1191], which is employed in various ways.
Native saltpetre is so rare, that Cronstedt was not acquainted with it.
At present, however, it is known to occur in the East Indies, in the
lower part of Italy, also in Portugal[1192], Spain, America, and some
other countries[1193]. But almost all the saltpetre obtained in Europe
is produced partly by nature and partly by art. The putrefaction of
organic bodies gives rise, under certain circumstances, to nitric acid,
which in general combines with calcareous earth wherever it finds it,
and forms the so-called earthy saltpetre. This is decomposed by potash,
and the latter uniting with the acid forms common saltpetre. Sometimes
also it is found that the nitric acid, instead of being united with
calcareous earth, is combined with soda, which produces the so-called
cubic saltpeter[1194]. Both these saline substances, but the earthy
more frequently than the cubic, are often found on effloresced walls;
and both are then comprehended under the common names of _Mauersalz_ or
_Mauerbeschlag_, _sal murale_.
This efflorescence on walls was observed, in all probability, at a
very early period, especially as it is produced in many parts in great
abundance, and as it makes itself perceptible by the decay of walls,
which it seems to corrode. It is the plague or leprosy of houses
mentioned in the Mosaic code of laws. As the ancients were so much
inclined to expect medicinal virtue in all natural bodies, there is
reason to think that they soon collected and made trial of this saline
incrustation. That this indeed was actually the case, and that they
gave the name of _nitrum_ to this saline mass, may be proved from their
writings. Their _nitrum_, however, must have been exceedingly various
in its properties. For this incrustation is not always calcareous
saltpetre; it is often soda[1195], mixed with more or less calcareous
earth; and sometimes it consists of salts of sulphuric acid. In
modern times, on closer examination, other salts of nitric acid have
been found in the incrustation of walls, such as flaming saltpetre or
nitrate of ammonia, bitter saltpetre or nitrate of magnesia; but of
these no mention can be expected in the works of the ancients.
Substances so different ought not indeed to have been all named
_nitrum_; but before natural history began to be formed into a regular
system, mankind in general fell into an error directly contrary to that
committed at present. Objects essentially different were comprehended
under one name, if they any how corresponded with each other even in
things accidental. Whereas at present every variety, however small,
obtains a distinct appellation; because many wish to have the pleasure,
if not of forming new species, at any rate of giving new names. The
elephant and rhinoceros were formerly called oxen; the sable and ermine
were named mice, and the ostrich was distinguished by the appellation
of sparrow. In the like manner, calcareous saltpetre and alkali might
be called _nitrum_. The ancients, however, gave to their _nitrum_ some
epithets, but they seem to have been used only to denote uncommon
varieties.
Now, as the ancients were not acquainted with any accurate method of
separating and distinguishing salts, it needs excite no wonder that
they should ascribe to their _nitrum_ properties which could not
possibly be united in a salt, and much less exist in our saltpetre.
But as they were neither acquainted with aquafortis nor manufactured
gunpowder, and as no particular use of calcareous saltpetre was known,
the _nitrum_ most valuable to them must have been that which consisted
chiefly of soda, and which consequently could be employed in washing,
in painting, and in glass-making.
It is well known that in warm countries this alkali effloresces here
and there from the earth, particularly in a dry soil, and even in
such quantity as to be employed in commerce. Hence it may be readily
comprehended why this effloresced salt, which is very often mixed with
common salt, obtained the name of _nitrum_.
The important discovery, that a similar salt, having the like
properties, and applicable to the same uses, named at present soda,
may be obtained from the ashes of certain plants, was first made, in
my opinion, by the ancient Egyptians or Arabians[1196]. This salt
also, at least by the Greeks, was named _nitrum_, or considered as a
species of it. By the incineration of the plants this salt was rendered
slightly caustic; and it then became moist in the air, and deliquesced
when not preserved in very close vessels. It was therefore like those
salts which are obtained, in the same manner, from the ashes of all
other plants; though the latter are essentially different from the
former, and in the course of time obtained the peculiar appellation of
potash or pearlash. One can hardly be surprised that the ancients were
not able to distinguish soda from potash, especially as they were both
obtained from vegetable ashes.
But were the ancients, under the ambiguous name of _nitrum_, acquainted
with our saltpetre? There is certainly reason to think that it became
known to them by lixiviating earths impregnated with salts. There are,
as already said, not only in India but also in Africa, and particularly
in Egypt, earths which, without the addition of ashes or potash, give
real saltpetre, like that of the rubbish-hills on the road from new
to old Cairo[1197], and like the earth in some parts of Spain. It is
a knowledge only of this natural kind of saltpetre, which required no
artificial composition, that can be allowed to the ancients, as it does
not appear by their writings that they were sufficiently versed in
chemistry to prepare the artificial kind used at present.
But even admitting that they had our saltpetre, where and by what
means can we be convinced of it? Is it to be expected that any of the
before-mentioned characters or properties of this salt should occur in
their writings? They neither made aquafortis nor gunpowder; and they
seem scarcely to have had any occasion or opportunity to discover its
deflagration and the carbonization thereby effected, or, when observed,
to examine and describe it. No other use of our saltpetre which could
properly announce this phenomenon has yet been known. How then can it
be ascertained that under the term _nitrum_ they sometimes meant our
saltpetre?
Those inclined to believe too little rather than too much, who cannot
be satisfied with mere conjectures or probabilities, but always require
full proof, will acknowledge with me, that the first certain accounts
of our saltpetre cannot be expected much before the invention of
aquafortis and gunpowder. It deserves also to be remarked, that the
real saltpetre, as soon as it became known, was named also _nitrum_;
but, by way of distinction, either _sal nitrum_, or _sal nitri_, or
_sal petræ_. The first appellation, from which our ancestors made
_salniter_, was occasioned by an unintelligible passage of Pliny,
which I shall afterwards point out. The two other names signify,
like _sal tartari_, _sal succini_, a salt which was not _nitrum_ but
obtained from _nitrum_. _Sal-nitri_, therefore, or _salniter_, was
that salt which, according to the representation of the ancients, was
separated by art from _nitrum_, yet was essentially different from the
_nitrum_ or soda commonly in use. Biringoccio says expressly, that
the artificial _nitrum_, for the sake of distinction, was named, not
_nitrum_, but _sal nitrum_.
The name _nitrum_ is of great antiquity, and seems to have been
conveyed from Egypt and Palestine to Greece, and thence to Italy and
every part of Europe. For it is evidently the _neter_ mentioned by
the prophet Jeremiah, chap. ii. ver. 22; and which occurs also in the
Proverbs of Solomon, chap. xxv. ver. 20. But whether the name _nitrum_,
as Jerome says[1198], be derived from the Egyptian province _Nitria_,
whence it was exported in great abundance, or the name of the province
was derived from _nitrum_, is a question of little importance in
regard to this research. _Nitron_ is mentioned by Herodotus, where he
describes the Egyptian method of embalming dead bodies[1199]; by some
of the Greeks the word was written and pronounced _litron_. In the same
manner people say _nympha_ and _lympha_. In order to avoid confusion, I
shall here call the _nitrum_ of the ancients nitrum, and the _nitrum_
of the mineralogists saltpetre.
In the course of time men became acquainted with the purer, more
useful, and cheaper mineral alkali which was furnished, under the name
of soda, by the Moors and inhabitants of the southern countries, who
had learned the method of preparing it. The vegetable alkali also was
always more and more manufactured in woody districts, as an article in
great request, and sold under the name of potash, _cineres clavellati_.
All knowledge of the impure alkali from the incrustation of walls
was then lost; and as there was no further need of guarding against
confusion, it was not longer thought worth while to name saltpetre _sal
nitri_: it was called _nitrum_; and the oldest signification of this
word being forgotten, it was admitted without further examination, that
the _nitrum_ of the ancients was nothing else than our saltpetre.
In the sixteenth century some learned Europeans, while travelling
through the East, heard the name _natrum_ given to the mineral alkali
which was then exported as an article of commerce, and introduced in
their works this transformation of the ancient word _nitrum_. This
appellation was employed by the systematic mineralogists, who, giving
themselves little trouble about the original meaning of words, and
taking care only to avoid confusion, called the mineral alkali also
_natrum_, and applied the name of _nitrum_ to saltpetre. As far as
I know at present, it was first stated by Peter Bellon and Prosper
Alpinus[1200], that the mineral alkali was in the East called _natrum_.
The former returned in 1549, and the latter was still in Cairo in 1580.
This word was adopted in mineralogy by Linnæus, in the year 1736, as
the name of a species, in which he comprehended for the first time
the alkaline incrustation found on walls. In this he is followed
by Wallerius, who includes also the mineral alkali from the East.
Afterwards the word _natrum_ was employed in the same sense by all
mineralogists.
It deserves here to be remarked, that Boyle had even examined and
determined the difference between the fixed and volatile alkalies; but
that mineralogists and chemists, till the latest periods, believed that
all fixed alkali arose, or at least was obtained, by the incineration
of plants. The difference between the mineral and vegetable alkalies
was first defined, in a proper manner, by the exertion of the German
chemists Pott, Model and Marggraf[1201]; especially after the last had
proved, in the year 1758, that the basis of common salt was not, as had
before been generally believed, an alkaline earth, but a fixed alkali,
to which, because it was in many of its properties different from the
fixed vegetable alkali, he gave the name of fixed mineral alkali. Soon
after this substance was discovered in mineral springs; and Model and
others have shown that it is not essentially different from that which
in the East is called _natrum_.
It is singular, and yet may be accounted for, that since that time many
have spoken of the _nitrum_ and _natrum_ of the ancients, though they
are only different pronunciations of the same word; and _natrum_ is
never found in the works of the Greeks or the Romans, and not even in
writings of the middle ages.
But if the greater part of what I have here said should be considered
only as conjecture, it must nevertheless be acknowledged that it is
deduced from the nature of the thing; and when impartially compared
with what we read in the ancients, the latter I hope will be better
understood than it hitherto has been; the impropriety of many readings
will become apparent, and the truth of this conjecture be admitted.
Were I here to relate everything that we read of _nitrum_, in order
to compare it with nature and to examine it thoroughly, I should be
obliged to extend this article to a greater length than might be
agreeable to the reader. I shall therefore give only the principal
proofs of my assertion, premising, that doubts which might be excited
by single passages not here mentioned, will, on a closer comparison,
vanish without my assistance. But I maintain that those who wish to
explain the old names of natural objects must relate everything said
of them, and not that alone which is favourable to their opinion, and
which may be often contradicted by what was purposely or accidentally
concealed. The first part of such an examination is always a careful
collection from the writings of the ancients of all the predicates of
the natural object, the systematic name of which one is endeavouring to
prove.
There is reason however to conjecture, that the ancients, in the
history of their impure nitre, the manner of obtaining which the Romans
at least had no opportunity themselves of seeing, for Pliny says
expressly that it was not procured in Italy, fell into many errors and
mistakes, which at present cannot all be explained.
Hence it happened that the ancients did not understand the art of
purifying the salt which they obtained from minerals; and therefore
they were obliged to use it in the same impure state in which they
found it. On this account they considered each natural mixture as a
peculiar kind; gave to the greater part of them, or those most useful,
particular names; and of these recommended for different purposes those
which, according to their purity or mixture, or according to other
circumstances, were the most convenient. It is not probable that all
these varieties could be again found out or defined; and it seems to be
of little importance, when it is known that the names denote nothing
more than the varieties of a mineral.
In this examination it is to be regretted that the book of
Theophrastus, in which he expressly treated of _nitrum_, has not been
preserved. But it may be believed, even without the testimony of Pliny,
that he was one of the most accurate and acute naturalists among the
ancients, and that he gave the best account of this substance[1202].
It must, however, be admitted that Pliny thoroughly understood this
author, and gave a correct extract from him, and that the transcriber
fell into no mistake.
That the _nitrum_ of the ancients was an alkali more or less impure,
but not saltpetre, has been long admitted by those who had the least
knowledge of mineralogy, as well as by the most sagacious physicians.
The grounds for this opinion, as far as I have yet learned, are as
follows: more indeed might be found, but these are sufficient to afford
a complete proof. Galen, a cautious writer, says that _nitrum_ was in
general burnt, by which means its effects were strengthened[1203]. Had
it been saltpetre, it is impossible that the ancients should not in
burning it have observed its deflagration, and this property is too
remarkable not to have been mentioned. But nothing is to be found that
can with any probability be supposed to allude to it.
But should it be admitted without any grounds that it was not an alkali
but saltpetre which they burnt, it must certainly have been carbonized;
for a burning body may easily have fallen into the crucible, and in
general _nitrum_ seems to have been burnt in an open fire, like our
lime, because Pliny, speaking of the Egyptian, considers the contrary
as somewhat uncommon. Physicians then, at any rate, must have observed,
that a body very different both in its appearance and effects was
produced from saltpetre by burning, but which could not be used for any
other purpose than that salt. Of this however we do not find the least
intimation.
But _nitrum_ was undoubtedly soda, and on that account when burnt must
have become more caustic as well as stronger in most of its effects,
and in this respect similar to potash, since [owing to impurities] it
in the same manner became moist and deliquesced in the air. What Pliny
relates of the Egyptian _nitrum_ becomes then intelligible. The latter,
he says, was transported in pitched vessels, because it would otherwise
have deliquesced; and he afterwards adds, that it was burnt before it
was sent off. Had he known that the latter was the cause and the former
the effect, he would have mentioned the latter first; but his whole
extract, in regard to nitre, is written in general without order. The
vessels, no doubt, were of clay; but whether he means in what he adds
that they were not burnt but only baked in the sun, or that before they
were filled they were completely dried in the sun, has been determined
by no commentator. To me the latter is the more probable. Pliny also
mentions another circumstance in regard to the burning of the Egyptian
_nitrum_; namely, that it must be done in a close vessel, otherwise
it would decrepitate or fly off. This is perfectly intelligible, when
it is considered that it contained a great deal of common salt, which
alone possessed the property of decrepitating; and it is well known in
mineralogy that native soda, and even that which in modern times has
been introduced into our collections from Tripoli, and of which I have
in my possession a specimen, contains common salt[1204], and often in
cubic crystals. Pliny had just reason to add, that _nitrum_ otherwise
does not properly decrepitate. The ancients were well acquainted with
the resemblance of their _nitrum_ to lime, and especially of that which
was burnt. On this account, because the Egyptian was exported after it
had been burnt, it could easily be mixed with quicklime, or, as Pliny
says, be adulterated. But the proof which he gives he does not seem to
have thoroughly understood. The Egyptian must at all times have been
caustic (_pungens_) even without lime; but that which was mixed with
lime could not so speedily or completely dissolve on the tongue as that
which was pure, and left behind it more earth. What he says of a test
by the smell, I cannot understand in any other manner than that burnt
lime, when moistened with water, diffused that disagreeable vapour
observed in apartments the walls of which have been newly plastered;
though when the quantity is small this is hardly perceptible.
If I understand Theophrastus[1205] properly, he seems to say, that
if _nitrum_ be burnt as soon as it is dug up, it communicates heat
to water in the same manner as lime. It may here be seen how great a
resemblance the ancients found between their _nitrum_, alkaline earth
and lime.
The similarity of wood-ashes to the _nitrum_ of the ancients, which
they acknowledged, proves also that it was in reality an alkaline salt.
We are told by Theophrastus[1206] that _nitrum_ was said to be produced
from oak-ashes; and Pliny[1207], who borrowed from this writer, remarks
that it was certain the ashes of that wood were nitrous. He ascribes
also to burnt wine-lees the nature and properties of _nitrum_[1208].
Nay he considers as a kind of _nitrum_ those saline ashes which, in
many countries destitute of salt, were used for seasoning food, and
which were prepared by pouring sea-water or salt brine over burning
piles of wood, gradually and in small quantities, so that the fire was
not extinguished, by which means the water evaporated, leaving the salt
behind, but mixed indeed with charcoal, ashes, earth, and alkaline
salts; consequently it must have been moist, or at any rate nauseous,
if not refined by a new solution. This method of preparing or boiling
salt, which perhaps is the oldest, has been mentioned by various
writers; but many of them, through ignorance or neglect, have not told
us that sea-water or brine was employed, as they speak in such a manner
as if any kind and even fresh water had been used for that purpose.
Varro relates that he saw this process employed on the Rhine[1209].
Pliny says[1210] that oak timber had before been burnt for that
purpose. In another place he mentions a similar process among the
Gauls and the Germans[1211], as Tacitus does among the Hermanduri
and the Catti[1212]. The former also states, on the authority of
Theophrastus, that the Umbri burnt salt in the like manner[1213]. It is
however certain that Pliny and other ancient writers often quote from
Theophrastus what, at present, is not to be found in the works of that
naturalist, but in those of his preceptor Aristotle[1214].
Pliny adds, that this paltry method of obtaining salt had been long
given up; and this indeed was the natural consequence of increased
civilization. It is however certain that it was long continued in many
countries, and in some still exists.
About two centuries ago the inhabitants of the province of Zeeland,
descendants perhaps of the Catti, used no other salt than what
they obtained in the like manner, from mud thrown up by the sea,
which they burned and moistened with sea-water, as we are told by
Lemnius, who was himself a native of that country. Boxhorn says, in
his annotations on the above-quoted passage of Tacitus, that he saw
a painting at Zirkzee, in which the whole process was represented.
It is probable that salt was boiled exactly in the same manner as at
some of the Sleswic islands, described by Denkwerth[1215], from whose
account it is seen that the _glebæ marinæ_, of which Lemnius speaks,
consisted of mud mixed with roots growing in them; and that the salt
when afterwards refined was called there Frisic, in all probability
because the inhabitants had learned to make it from their ancestors the
Frieslanders. I remember somewhere to have read that salt was made for
a long time in this manner by the so-called Wurst-Frieslanders, in the
country of Wurst, belonging to the duchy of Bremen. The inhabitants
also of the Austrian part of Moldavia, or Buccowina as it is called,
still use a salt, which they do not boil, but burn with their
superfluous wood, in the like manner from the brine of a saline spring.
A member of the former Academy of Brussels[1216] took the trouble to
examine the process as described by the ancients, and obtained, as
might certainly have been expected, a highly alkaline kind of common
salt, similar to that which Pliny, not without reason, considered as
a sort of _nitrum_, because undoubtedly it may oftener have been an
alkaline carbonate than common salt.
Boerhaave[1217], in quoting the passages of the ancients, did not
reflect that, during the incineration of the wood, salt water was
poured over it. He considered the whole process as a burning of potash,
and thought that the salt obtained was fit for use only because it
was made according to the manner of Tachenius. That indeed gives a
carbonated salt, which is almost saponaceous, and so mixed with
various parts of the burnt plants that it is much milder, consequently
fitter for use than common soda or pearlash can be; but that salt
was not so much of the Tachenian kind as a species of common salt
superabundant in alkali.
If the _nitrum_ was carbonated alkali, there is reason to suppose that
the ancients must have occasionally mentioned in their writings that
it effervesced with acids. With the mineral acids indeed they were
not acquainted; but they had vinegar, and that _nitrum_ produced with
this an effervescence had been known in the oldest times. A very clear
allusion to this circumstance is found in the book of Proverbs, chap.
xxv. ver. 20; where Luther however translates the word by _chalk_.
Jerome, whose explanation I have already quoted, was in some degree
acquainted with this phænomenon; and therefore to him the comparison of
Solomon was intelligible[1218]. But at present I can produce no proofs
from Greek writers; though they might have occurred during the use of
_nitrum_ in medicine, in consequence of which it was often put into
vinegar.
We shall be further convinced what _nitrum_ really was, when the uses
to which it was applied, as mentioned in the works of the ancients, are
considered. The most common, as soap was not then known, appears to
have been in washing, a purpose for which our saltpetre would not be
fit; besides, it is at all times too scarce and too dear. I shall not
here adduce any proofs of its being employed in this manner, as they
often occur, and as several have been already given in the preceding
volume[1219]. Many salves and cosmetics were prepared with _nitrum_;
and in all probability articles of this kind, used chiefly among the
women, are to be understood by the term _nitron parthenicon_, which
occurs in Nicholas Myrepsius, in the beginning of the fourteenth
century; _matronicon_, mentioned by the same, and by Alexander of
Tralles, about the year 565; and the _nitrum matronale_ of Marcellus
Empiricus, in the fifth century. That the use of it for washing still
continues in the East, is confirmed in various books of travels.
The oldest glass, of the preparation of which any account is to be
found in history, was made by means of _nitrum_ or mineral alkali. For
though I doubt that it could have been produced on the sandy banks of
the Belus, where some merchants, when cooking, supported their pots
with lumps of _nitrum_[1220], because sand is not so easily brought to
a state of fusion; it at any rate remains certain, that this supposed
fusion with our saltpetre is altogether impossible.
The use of _nitrum_ for painting announces, without doubt, an alkaline
carbonate, and not saltpetre[1221]; and the case is the same with
the various uses in the cookery of the ancients, many of which we
have still retained. It was added to bread in baking, according to
Pliny[1222], in the stead of salt, but probably to promote its rising,
for which purpose it is still employed by the Egyptians, as potash was
by our bakers. For this use the mineral alkali was formerly brought
from the Levant to France, till it was declared by the physicians to be
injurious to the health[1223].
When meat which was too fresh was to be dressed, it was put into
_nitrum_[1224], in order to make it tender; and, according to Forskäl
and others, this is still practised in the East. Our cooks also know
that smoked meat, fish and other dried provisions become more tender
when placed in a ley of potash, or when a little potash is added while
they are boiling.
_Nitrum_, however, was employed for curing articles of food which
people wished to preserve. This appears to contradict what has been
mentioned above; but in all probability a caustic sort was used for the
former purpose; but for the latter a mild kind, mixed with a great deal
of common salt. There were so many species, that some of them might
have been applied to quite contrary purposes.
As I conjecture, the use of _nitrum_ for causing chestnuts and other
husky fruits to boil soft, was also known: to produce the same effect,
potash is at present thrown among boiling lentils and peas. I am
inclined to think that for this reason Apicius caused chestnuts to be
boiled with nitre.
It is highly probable that this effect of alkaline carbonates induced
agriculturists to believe that beans, peas, lentils and other
leguminous fruits, if steeped, before they were sown, in water in
which nitre had been dissolved, or if the dung spread over the earth
had been mixed with nitre, the future product could be more easily
boiled soft[1225]. However useful this addition may be in cookery, it
would produce little effect on seed; and it appears to me that the
old agriculturists placed little confidence in the last-mentioned
use, because they were not agreed in regard to the result. Virgil
and others seem to expect from it an increase of the fruit[1226];
but others, security against beetles, which eat the fruit and leave
the husks empty[1227]. When cabbages were transplanted they were
strewed over with nitre, and by these means were said to come sooner
to maturity[1228]. Radishes also were treated in the same manner, or
besprinkled with nitrous water, in order to make them more tender[1229].
A common method employed by the ancient cooks to give a beautiful
green colour to pickled or boiled vegetables, was to add _nitrum_ to
them while boiling; but this effect could be produced by _natrum_,
and not by the _nitrum_ of the moderns, or that neutral salt called
saltpetre[1230].
Among the oldest accounts of _nitrum_ is that where it is mentioned
as being employed for embalming dead bodies. It would be tiresome
to read over and examine everything written on that subject by the
learned; but this much I think is clear, that either the flesh, and in
general the softer parts of the body could be corroded in the course
of seventy days by the Egyptian nitrum[1231], which, as above shown,
was burnt, and in general mixed with unslaked lime, and consequently
caustic[1232]; or that the moist parts could be desiccated by carbonate
alkali, in the same manner as the manufacturers of parchment purify and
dry their skins by the application of chalk. That saltpetre in no case
could be useful for this purpose needs hardly be mentioned.
The ancient physicians, who were unacquainted with our numerous class
of salts, employed their _nitrum_ in many ways, and for a great variety
of mixtures; but no writer, as far as I know, ever took the trouble
to examine these recipes, though it has long since been declared that
_nitrum_ must have been potash or salt of tartar. Matthioli[1233]
asserted, that those physicians would act very improperly who should
prescribe our saltpetre where the ancients employed their _nitrum_;
and indeed those in the least acquainted with the effects of salts
must know, that all those extolled by the ancients announce carbonated
alkalies. Thus burnt _nitrum_ was employed for cleaning black teeth, as
at present many use tobacco ashes instead of tooth-powder. It is seen
by the works of Aretæus and others, that burnt _nitrum_ was used as a
caustic, till people learned in modern times to prepare the more active
_causticum potentiale_, or _sal causticum_.
What the ancients say of the taste of their _nitrum_ seems, however,
not entirely applicable to pure carbonated alkali; and much less, or
not at all, to our saltpetre. Had they meant the latter, they would
certainly not have failed to mention the sensation of coolness which
it occasions when applied to the tongue. Galen and Aetius say, that
_nitrum_ is as bitter as gall; but Serapio ascribes to it a saline
taste, with a small degree of bitterness; as does also Pliny, only that
for bitterness he substitutes the word sharpness. The names of tastes,
however, are as uncertain as the names of the colours which occur in
the works of the ancients. Both certainly deserve to be more accurately
examined, and to be defined by comparing the things to which these
names are given. Prosper Alpinus, however, is of opinion that what the
ancients called _amarum_, is not inapplicable to the taste of _natrum_.
The ancients mention various springs and streams which contained what
they called _nitrum_[1234]; but nitrous water, according to the present
acceptation of the word, that is, water which contains saltpetre, does
not exist; and if credit is to be given to Marggraf and others, that
they observed traces of saltpetre in some kinds of water, the instances
must have been so rare that mention of them could not be expected
among the ancients. Their nitrous water was undoubtedly alkaline, and
this indeed is not scarce. Such water was recommended by the ancient
physicians, both for bathing and drinking[1235]; and Pliny says, it was
singular that the salt of such water would not shoot into crystals,
like common salt, which is undoubtedly true[1236].
Alkaline water of this kind, such as that of Armenia, was used for
washing, and also by fullers. In Egypt, at present, people wash in the
same manner with _nitrum_.
It appears to me that many kinds of water, which were only impure and
not potable on account of their nauseous taste, were considered by
the ancients as nitrous. This seems to be proved by the means which
they propose for rendering nitrous water fit to be drunk; that is, by
throwing into it clay, or some grains of barley[1237]. In the like
manner, I saw the brewers at Amsterdam improve their dirty water, in
some degree, by putting into it kneaded clay, and allowing it to sink
to the bottom.
One foundation more for my assertion may be found, I think, in the name
_borax_. The ancient _nitrum_ by the Arabians was called _Bauracon_ or
_Baurach_. When that salt, which at present is everywhere called borax,
became known to the Arabians, it was at first generally considered as
a kind of nitre, and on that account called _Baurach_, because in most
of its properties it approached near to the _nitrum_ of the ancients,
that is, the _natrum_ of the present day. But afterwards, when the
difference became known, our borax, at least in Europe, retained
exclusively the general name of _Baurach_, from which at length was
formed the present word _borax_. My conclusion therefore is, that the
_nitrum_ of the ancients must have been mineral alkali; otherwise it is
impossible that our borax, which till modern times was reckoned to be
mineral alkali, should have been considered as a _nitrum_.
For many centuries past, the people in Africa and Asia, and also in
Spain and Sicily, have cultivated some kinds of plants, which they dry
and then burn to ashes. By regulating the fire in a particular manner,
they cause these ashes to assume a certain degree of concretion, or
vitrification, by which means they are formed into solid cakes of
a grey colour, interspersed with many white and black spots. This
substance, which in consequence of the vitrification does not become
moist in the air, is broken into fragments, and sent to every part
of Europe under the name of _soda_, for the use of the glass-houses,
soap-boilers, dyers, and for other purposes.
These plants were undoubtedly first cultivated and employed in Europe
by the Arabians, who made known the use of them. Those first or chiefly
employed were named by them _axnan_, _usnan_, _usnen_, or _uscnanon_;
and also _Hasciscio alcali_, that is, _herba kali_, the plant or herb
kali, because the name _kali_, or, with the article prefixed, _al
kali_, was not given to the plant but to the half-vitrified ashes
_kali_. Hence the chemists call salts obtained from the ashes of
plants, alkaline salts. I do not know how old this appellation may be;
but it is to be found in Vincent Bellovacensis and in the interpolated
writings of Geber and Avicenna, and particularly in a passage quoted by
the former from an old alchemist named Jahie, where it is called _sal
alchali_[1238]. All these salts formerly were considered as nitrous
salts, or a kind of _nitrum_. It was indeed soon observed that soda
and wood-ashes, which from the earliest periods had been burnt in
woody districts, and which are now called potash, were not all of the
same nature; but when the difference between the mineral and vegetable
alkalies began to be studied, it was then known that soda contains the
former, that is, our _natrum_, and potash the latter, but both indeed
often rendered impure by earthy and foreign saline particles; and that
there are many plants from the ashes of which mineral and not vegetable
alkali is obtained. A question now arises, How old in the Levant is the
method of preparing this _natrum_ from the ashes of plants?
Michaelis is of opinion that it is mentioned in Malachi, chap. iii.
ver. 2; which passage I shall give according to Luther’s translation:
“Who shall stand when he appeareth? for he is like the fire of the
goldsmith, and the soap of the scourer. He will sit and melt and purify
the silver, and make pure like gold and silver.” This learned man here
seems to think that the sacred writer alludes to refining the noble
metals, and that the word _borith_ means soda, which indeed may serve
as a flux in the purification of them. I at first considered this
meaning as true; but, on closer examination, I am fully convinced that
we have both erred.
Those who read without prejudice the above passage of Malachi, must
remark, that a double comparison or double image is employed. The
messenger there promised was to separate the good from the bad, the
clean from the unclean. The first occupation is compared with the
labour of the gold-refiner; the other, with that of the scourer of
clothes. The first image is afterwards heightened, because the poet,
in all probability, was desirous of applying the separation of the
ignoble parts, such as slag, by means of fire, as being the stronger
image which denotes punishment, in a closer manner to the Levites and
priests. At the time of the poet, before the invention of soap, people
employed for washing either nitre or the saponaceous juice of certain
plants, which I have already endeavoured to determine. The _borith_ of
the washer there expressly named, was undoubtedly one of these soap
plants, and not the half-vitrified ashes either of soda or potash.
This passage of Malachi was so understood in the oldest times.
Professor Tychsen, a true pupil and intimate friend of Michaelis,
to whose opinion I subjected my doubts, assured me that Michaelis
was never able to convince him of the justness of his exposition;
especially as Jerome[1239], without the least hesitation, understood
_borith_ to be a plant growing in Palestine, and used there for
washing; and as the Greek translators, who were much nearer to the
period of the poet, and could not be unacquainted with a thing so much
used, have translated _borith_ by the word ποα, a plant.
In Jeremiah, chap. ii. ver. 22[1240], both the substances formerly
used for washing, _nitrum_ and the soap-plant, are so clearly named,
that Michaelis was obliged to admit that we cannot understand there
soda or potash, but a ley or soap, the last of which however was not
at that time known. But, to speak the truth, potash and soda would not
be altogether unfit for washing; at any rate, not less fit than the
_nether_ or _nitrum_ there named. What may serve, however, to refute
entirely the opinion of Michaelis is, that no proof has yet been found
that soda is of so great antiquity. For my part, I am acquainted with
no older mention of it than that which occurs in the works of the more
modern Arabian physicians, Avicenna, Serapio, and others[1241].
All these grounds afford sufficient proof that the _nitrum_ of the
ancients was our _natrum_, and not our saltpetre. But still, in the
account given by the ancients of that salt, there remain many things
inexplicable. Thus, for example, no one can accurately define the
epithets, _chalastricum_, _halmirhaga_, _agrium_, _spuma nitri_,
_aphronitrum_, and others, because they do not indicate different
kinds, as already said, but accidental properties of the same salt.
Without enlarging further on this subject, I shall only remark that
Pliny admits a natural and an artificial kind of _nitrum_, and this
division is adopted by Serapio; but the latter term has not the meaning
which we affix to it at present. The ancients were acquainted with no
other than native _nitrum_, which they called artificial only when it
required a little more trouble and art to obtain it.
Most of the physicians recommend red _nitrum_, which is mentioned also
by many of the modern travellers. When Prosper Alpinus was in Egypt the
rose-red _nitrum_ cost twice as much as the white. The red colour, in
all probability, arises from a metallic admixture; yet the red _nitrum_
may be purer than the other, as red or violet rock-salt is often
clearer and purer than that which is colourless.
One of the darkest parts in the history of _nitrum_ is the following
passage of Pliny: “Faciunt ex his vasa, nec non frequenter liquatum
cum sulphure, coquentes in carbonibus.” The latter words he seems soon
after to repeat: “Sal nitrum sulphuri concoctum in lapidem vertitur.”
From these words J. Rhodius[1242] concludes that _nitrum fixum_ was at
that time known, because he considered _nitrum_ to be saltpetre; but in
that case with the sulphur, Glaser’s sal polychrest must properly have
been produced. This, however, was not the case, because _nitrum_ was
fixed alkali. The ancients therefore, when they placed it with sulphur
in a crucible upon burning coals must have obtained liver of sulphur,
which when it cools is hard, but soon becomes moist when exposed to the
air. But I will not venture to determine whether anything of this kind
is to be supposed in Pliny, who did not himself fully understand the
subject on which he touches.
The account of vessels made of _nitrum_ is still more singular.
Michaelis conjectured[1243] that articles of various kinds were cut out
of this substance, not for real use but merely for ornament, in the
same manner as similar things are cut out of rock-salt in Transylvania,
many specimens of which I have in my collection[1244]. But even if
_nitrum_ had been compact and strong enough for this purpose, there
could not be the same inducement to employ it as rock-salt, which, in
consequence of its solidity, transparency, brightness and smoothness,
appears to be capable of furnishing vessels equal to those made of
the most beautiful crystal. Dalechamp seems to explain the whole as
applicable to glazing; but in this case _nitrum_ could serve only as a
flux.
Though it can be certainly proved that the _nitrum_ of the ancients
was an alkaline salt, it is difficult to determine the time when our
saltpetre was discovered or made known. As many have conjectured that
it was a component part of the Greek fire, invented about the year 678,
which, in all probability, gave rise to the invention of gunpowder, I
examined the prescriptions for the preparation of it. The oldest, and
perhaps the most certain, is that given by the princess Anna Comnena;
in which however I find only resin, sulphur and oil, but not saltpetre.
Klingenstierna[1245] therefore judged very properly, that all recipes
in which saltpetre occurs are either forged or of modern invention.
Of this kind are those which Scaliger, at least according to his
own account, found in Arabic works, and in which mention is made of
_oleum de nitro_ and _sal petræ_[1246]. But it does not occur in that
prescription given by Marcus Græcus, and copied by Albertus Magnus, who
died in 1280[1247].
I must still believe that the first certain mention of saltpetre will
be found in the oldest account of the preparation of gunpowder, which,
in my opinion, became known in Europe in the thirteenth century, about
the same time that the use of the Greek fire, of which there were many
kinds, began to be lost. Among the oldest information on this subject
is that found in the above-quoted work of Albertus Magnus, and the
writings of Roger Bacon, who died in 1278. It is doubted whether the
first-mentioned treatise belongs to Albertus; but it is certain that
the author, whoever he may have been, and also Bacon, both derived
their information from the same source.
When M. von Arretin lately announced that he was about to publish
a manuscript preserved in the electoral library at Munich, which
contained the true recipe for making the Greek fire and the oldest
for gunpowder, the same writing, as appears, was printed from two
manuscripts in the library at Paris. I have now before me a copy of it,
which was transmitted to the library of our university by M. Laporte
Dutheil, conservateur des Manuscrits de la Bibliothèque[1248].
It contains many recipes, but only with a few variations, as in
Albertus Magnus; and it may be evidently seen that Roger Bacon employed
this writing, which is mentioned by Jebb in the preface to his edition,
from a copy preserved in the library of Dr. Mead. Of this Marcus
Græcus nothing at present is known. According to some, he lived in the
ninth century; but others, with more probability, place him in the
thirteenth. Of his work, perhaps, we have only a translation; for, from
the surname Græcus, there is reason to think that the original was
written in the Greek language. I must, however, remark that Cardan,
where he gives directions for making a fire which can be kindled by
water, names Marcus Gracchus, but not Græcus. Scaliger, who, as is
very probable, had this writing also, makes no mention of it or its
author.
This Marcus speaks of saltpetre three times; first under the name
of _sal petrosum_, which occurs also in the same prescription in
Albertus Magnus; but the addition, which Albertus does not repeat,
is very remarkable. In my opinion, _scrophulæ contra lapides_ means
the incrustation found on walls, which was represented as a kind
of leprosy. The addition of ashes, or alkaline salts, the author
either forgot or omitted, because perhaps he did not consider it as
indispensably necessary. In another place it is said, _Lapis qui
dicitur petra solis_, or, as it is in other manuscripts, _salis_; but
whether saltpetre is here understood I will not venture to determine.
In a third passage we find the words _de sale petroso_, or _de
salepetro_.
In the works of Bacon the term _sal petræ_ occurs at least three times.
According to Casiri, the term _pulvis nitratus_ is to be found in an
Arabic manuscript, the author of which lived about the year 1249[1249].
If the work of Geber, already quoted, be genuine, and if this writer
lived, as some think, in the eighth century, it would be the oldest
where saltpetre is mentioned, in a prescription for an _aqua solutiva_
or _dissolutiva_, which almost seems to be aqua regia. I have not
observed the name _sal petræ_ in the works of Vincent Bellovacensis,
who lived in the thirteenth century.
In a word, I am more than ever inclined to accede to the opinion of
those who believe that gunpowder was invented in India, and brought
by the Saracens from Africa to the Europeans, who however improved
the preparation of it, and found out different ways of employing it
in war, as well as small arms and cannon[1250]. In no country could
saltpetre, and the various uses of it, be more easily discovered than
in India, where the soil is so rich in nitrous particles that nothing
is necessary but to lixiviate it in order to obtain saltpetre; and
where this substance is so abundant, that almost all the gunpowder
used in the different wars with which the sovereigns of Europe have
tormented mankind was made from Indian saltpetre[1251]. If it be true
that saltpetre was not known in Europe till the thirteenth century,
neither gunpowder nor aquafortis could have been made before that time;
for the former cannot be prepared without saltpetre, nor the latter
without nitre. But if it be true that this salt was known at a much
earlier period in India, it is not improbable that both gunpowder and
aquafortis were used by the Indians and the Arabians before they were
employed by the Europeans, especially as the former were the first
teachers of chemistry to the latter. In my opinion, what I have already
related proves this in regard to gunpowder; and what I shall here add
will afford an equal proof in regard to aquafortis.
It is difficult to discover the first mention of mineral acids in the
writings of the ancient chemists. In the course of their numerous
experiments they obtained indeed, at an early period, acids, the
utility of which they extol; but each concealed the process by which
they were made; and as they had no method of obtaining them pure, they
were for a long time unacquainted with the difference between the
kinds. Their prescriptions, when they are found, are so contradictory
and so carelessly written, that it is almost impossible to conjecture
which of the known acids forms the principal component parts in their
recipes or mixtures.
It appears to me, that the first intelligible account of aquafortis
occurs in the writings of the Arabians, or of the pupils of Arabian
chemists. At present I am acquainted with none older than that to be
found in the works of Geber. For though I do not believe that those
of which we have Latin translations belong to a Geber of the eighth
or ninth century, I am ready to admit that they may be, at any rate,
of the twelfth. This appears probable, because about that period
aquafortis and various arts are oftener mentioned, and in a much
clearer manner, in these writings.
It is to be regretted in the history of chemistry, that it is
impossible to determine the period of the Greek chemist or alchemist
known under the name of Synesius; but it cannot be doubted that he
borrowed a great deal from the works of the Arabians. This Synesius,
among the chemical solvents, mentions water of saltpetre, which might
be considered as aquafortis[1252]. But, as he mentions at the same
time _aqua fæcis_, he appears to me to allude to the _nitrum_ of the
ancients, not to our saltpetre, and in general to strong alkaline leys,
which indeed are capable of dissolving many bodies.
The monk Theophilus, of whom I have already spoken, and who in all
probability lived in the twelfth century, appears also to have been
acquainted with aquafortis; for in some of the passages quoted from
his works by Raspe[1253], he speaks of an acid which dissolved all
metals. In the writings of Vincent Bellovacensis, in the thirteenth
century, some traces, but very doubtful, are found of aquafortis. Where
he mentions the different sorts of gold he speaks of dissolving it,
but by this expression he does not allude to its treatment with fire,
which he speaks of separately[1254]. In another place he mentions the
different solvents, and among these names vegetable acids, a water of
sal-ammoniac, and a water obtained from alum by distillation. He here
means undoubtedly a mineral acid[1255]. Michael Meier, the most learned
chemist of the seventeenth century, says that Vincentius speaks of
aquafortis as of a secret; but the passage I have not yet been able to
find[1256].
Spielman states that Lullius, who died in 1315, in the eightieth
year of his age, gave an account of his obtaining aquafortis from
saltpetre by the addition of vitriol, and that Basilius Valentin was
acquainted with the use of clay for the same purpose. Picus Mirandula
however declares it to be uncertain whether Arnoldus de Villa Nova was
acquainted with the acid of saltpetre in the fourteenth century.
It appears to be an old tradition that this acid was first employed
at Venice, by some Germans, for separating the noble metals, and
conveyed thence as an article of merchandize to every part of Europe.
The persons who prepared it were there narrowly watched, in order
that the process might not become known. They were employed chiefly
for separating the gold from the Spanish silver, and by these means
acquired great riches. Hence arose the report that the people of
Venice understood the art of making gold; and it is certain that in
many countries the gold refiners were for a long time considered as
gold makers; but in no period were there more gold makers than in that
when separation in the moist way became known. I can however give less
account of this art of the Venetians than of the introduction of it
into France in the fifteenth or the beginning of the sixteenth century.
William Budæus, who was born in 1467, and died in 1540, speaks of it
in his book, printed for the first time in 1516, as a thing entirely
new at that period[1257]. A man of low extraction, named Le Cointe,
first undertook to separate gold from silver at Paris, by means of
a water which Budæus calls _aqua chrysulca_. It is very remarkable,
that by means of this water he could separate the smallest particle of
gold from silver, and from every other metal; nay, he could even take
from vessels their gilding without altering their form. By this art he
acquired great wealth; which together with his secret descended to his
son, who at the time was the only gold refiner at Paris.
He adds, that the art was exceedingly dangerous as well as unhealthy,
and required great precaution. The possessor of it, when he became
rich, left the execution of the work to a servant, whom he directed at
a distance, that he might not expose himself to the pernicious fumes of
the effervescing liquor. The fumes of the acid derived from saltpetre
are indeed prejudicial to the health; but the danger has been much
exaggerated, and no doubt with a view to deter people from attempting
to discover the art, and to furnish a pretence for raising the price of
the production[1258].
Budæus relates also, that the gold was left behind undissolved. The
silver only was dissolved, and by another art was separated from the
water and washed. It may here be easily perceived that Le Cointe
employed aquafortis; but if he was able to loosen the gold from gilt
vessels without destroying them, he must have used aqua regia, which
consequently was not then unknown.
From other information, it appears that the mint at Paris purchased
the art from Le Cointe’s son, but still kept it a secret. On this
account Francis I., by a decree issued at Blois on the 19th of March
1540, authorized the raising the value of coin, in order to defray the
expense of fuel and assaying-water. In the middle of the seventeenth
century, the preparation of aquafortis and the process of assaying in
the moist way were fully known in France. At any rate, in the month
of January 1637, the distillers obtained a guild letter, in which
aquafortis is mentioned among the articles sold by them.
When saltpetre became necessary to governments for the manufacture
of gunpowder, they endeavoured to obtain it at as cheap a rate as
possible. No one before suspected that rulers would be justified in
exclusively carrying away the incrustation of walls from private
houses, which, when it could be used, became _accessorium fundi_.
But the idea of regalia, so often abused, was extended so wide under
various pretences, that the saltpetre regale and the letting of it
was one of the severest oppressions to which the people were exposed
by their rulers, and which occasioned almost as bitter complaints as
the hunting regale, founded on no better grounds. I shall not here
attempt to delineate the sufferings which were thus occasioned in many
countries; they are still fresh in remembrance.
The oldest mention of this hated regale which I myself have found is
of the year 1419. At that time, Gunther, archbishop of Magdeburg,
granted to some person the right of searching out saltpetre and boiling
it, during a year, in the district of Gibichenstein, for which he
was to pay a barrel of saltpetre, and deliver to the archbishop the
remainder at the rate of five cross-groschens per pound. The succeeding
archbishop, Frederick, let in the year 1460, to a burgher of Halle,
all the earth and the saltpetre that could be collected from it in
the bailiwick of Gibichenstein, for four years, at the annual rent of
a barrel of good refined saltpetre. On the same conditions, bishop
Ernest, in 1477, let to some one for his lifetime the collection of
the saltpetre. In 1544, a certain person obtained the collection
of saltpetre from two heaps of rubbish before the gates at Halle.
The magistrates of Halle also in 1545 had a saltpetre-work and a
powder-mill. In the year 1560, John VI., archbishop of Triers, gave to
some one permission to search for and dig up saltpetre. In 1583, the
saltpetre regale was confirmed by a Brandenburg decree as a thing long
known, and the case was the same with a Hessian of the year 1589.
It is very probable that this example was soon followed by most
sovereigns; but even if they had collected and scraped together the
nitrous incrustation of all the walls in Europe, they certainly would
not have found a quantity of saltpetre sufficient for the gunpowder
used in the numerous wars which took place, had not a much greater
supply been obtained from India, and particularly from Patna. I do not
know whether the Portuguese brought this article to Europe; but that
it was imported at a very early period by the Dutch is proved by the
oldest ladings of their return ships; and they at length found means to
appropriate this branch of trade so entirely to themselves, that the
other Europeans for a long time could not obtain any saltpetre in India.
In the seventeenth century, when chemistry began to be studied with
more care and attention in Europe, and particularly in Germany, and
the component parts and production of saltpetre became better known,
many conceived the idea of improving the methods of obtaining it
in Europe so much, that it might be possible to dispense with the
Indian saltpetre, and flattered themselves with the hopes of thence
deriving great advantages. Some proposed to fill tubes with putrifiable
substances and earth capable of fixing of the nitric acid; others
preferred building vaults of these substances, and Glauber recommended
the filling of pits with them. The proposal, however, which met with
the greatest approbation was that of building walls of them. Through a
confidence in this idea, towns and villages were compelled to erect and
maintain a certain number of saltpetre walls, under the most gracious
promise that the collectors of saltpetre should no longer be allowed
to spoil private dwellings, or render them unhealthful.
But experience has shown that all the means and coercive measures
hitherto employed have rendered the European saltpetre much dearer
than that obtained by commerce from Bengal. This will be readily
comprehended, when it is known that earth richly impregnated with
saltpetre abounds in India, and that it may be extracted by lixiviation
without any addition, and brought to crystallize in that warm climate
without the aid of fire; that the price of labour there is exceedingly
low; that this salt is brought from India instead of ballast by all
the commercial nations of Europe, where the competition of the sellers
prevents the price from ever being extravagantly high, while the
preparation of it in Europe, in consequence of the still increasing
price of labour, fuel and ashes, is always becoming dearer. This regale
will at length be everywhere scouted. In the duchy of Wurtemberg and
the Prussian states, where it was most rigidly enforced, in consequence
of an urgent representation from the States it was abolished in 1798;
but in both countries an indemnification was given to government for
the loss. The case also has been the same in Sweden[1259]. In the
duchy of Brunswick it was soon suffered to drop; but in the electoral
dominions it never was introduced.
[The greater part of our nitre is derived from Bengal, where, as in
Egypt, Persia, Spain, &c., it exists in the soil. It is separated by
lixiviation and crystallization. In France, Sweden and some other
countries it is prepared artificially in nitre-beds. These are formed
of various animal matters, mixed with lime or mortar-rubbish; the
mixture is watered and stirred occasionally, and allowed to remain
for a considerable time. The whole is then lixiviated and decomposed
by carbonate of potash. The nitre is then separated and purified by
crystallization. In some cases wood-ashes are mixed with the animal
matters; the decomposition with potash is then unnecessary.
It is a question whether the nitric acid in the nitre arises from the
nitrogen of the atmosphere or that in the animal matters. Dr. Davy
has found nitre in a cave at Ceylon, where no nitrogenous matter was
present; and in some parts of India, Spain, and some other countries,
at a distance from all habitations, immense quantities of nitre are
reproduced in soils which have been washed the year before. Nitre
is directly brought into this country from Calcutta and Madras, in
bags containing from 150 lbs. to 175 lbs. each. From 200,000 cwts. to
260,000 cwts. are annually imported into the United Kingdom.
In making gunpowder, the components, the sulphur, nitre, and charcoal
should be as pure as possible, and reduced to the finest possible
powder; they are sifted and mixed in the proper proportions. The
mixture is then made into a cake with water, and ground between
calcareous millstones. It is then granulated through sieves in
another mill, and again sifted. It is then polished and hardened by
revolving rapidly in a cask, and finally dried. The proportions of the
constituents vary in different countries; at Waltham Abbey they are
seventy-five nitre, fifteen charcoal and ten sulphur. The quantity of
gunpowder consumed in this country is enormous; moreover, 4,000,000
lbs. are annually exported, the greater part of which is sent to the
western coast of Africa.
The force of the explosion of gunpowder is owing to the sudden
disengagement of gaseous products; these consist of nitrogen, carbonic
oxide, carbonic acid, and sulphurous acid gases; and their volume has
been calculated to amount to 2000 times the bulk of the powder.]