THO’ iron is universally allowed to be one of the most powerful
medicines now in use, yet many physicians observing, that the _fæces_
of patients, who used it either in a metallic or saline form, were
tinged of a black colour, have been led to think, that, in a metallic
state, it could not be reduced into particles fine enough to be
received by the lacteal vessels; and if taken in a saline form, that
it underwent a precipitation in the intestines, by which, being
reduced to an earth or calx, it was in like manner rendered incapable
of making its way into the blood. But the accurate experiments, with
which Signor Menghini has favoured the public in the Memoirs of the
Bononian Academy[34], sufficiently prove, that the ore and filings of
iron, finely levigated, enter the blood in considerable quantity; as
does also the _crocus_, _calx_, or earthy part of the metal, tho’ in
less proportion than the two former, which were found to act with a
violent _stimulus_ on the vessels, and to have dissolved and broke the
_crasis_ of the blood of different animals, that had used them for some
weeks in large doses mixed with their ordinary food. Tho’ it must be
allowed, that these experiments are very curious, yet the subject seems
to require a further inquiry, viz. _Whether iron is capable of entering
the blood in a state of solution, or under a saline form_: for, from
the violent _stimulus_, as well as from the dissolution of the blood,
and other symptoms brought on by the use of the ore and filings, these
substances (not being properly dissolved) appear to have acted in a
manner so grossly mechanical, that, whatever Signor Menghini may think,
very little is to be concluded from them, with regard to the action of
iron on the human body, in such cases, as indicate its use, and where a
rational physician would think proper to prescribe it as a medicine.
Having read Signor Menghini’s memoir, I recollected, that in the year
1753 I had, with the assistance of two friends, made the following
experiment, in order to discover, whether iron, in a saline form, is
capable of entering the lacteals.
An ounce and a half of salt of steel dissolved in a sufficient quantity
of water, filtrated and mixed with about a pound of bread and milk,
were forced down the throat of a dog, that had been kept fasting for
36 hours. An hour after he had swallowed this mixture, having secured
him in a supine posture, as is usual in such experiments, we opened the
abdomen, and observed the lacteal vessels, like white threads, running
along the mesentery in a very beautiful manner. Upon slitting open part
of the small guts, we there found a good deal of the mixture, which
appeared frothy, but without any black colour, or the least sign of the
salt being precipitated; and struck a deep inky colour with infusion
of galls. Tho’ the white colour of the lacteals convinced us, that
they were full of chyle, yet, as it would have been impossible to have
collected a sufficient quantity of it from them, we found it necessary
to open the thorax, and tie the thoracic duct a little above the
receptacle, which, from the ligature, soon became turgid, the animal
being alive and warm, and the chyle still continuing its course towards
the thoracic duct. Having cut open the receptacle, we easily collected
a sufficient quantity of chyle, and immediately mixed therewith, drop
by drop, infusion of galls; a very simple and easy method, by which an
incredibly small quantity of salt of steel may be discovered in most
liquors: but not the smallest change of colour was observed, tho’ they
were rubbed together for some time, and allowed to stand several hours.
Now had there been a single atom (so to speak) of the salt in so small
a portion of chyle, as that used in this experiment, which was, as near
as I could guess, some what less than half an ounce, it is not to be
imagined, that it could have failed to discover itself by this method
of trial; for upon adding one fourth of a grain of the salt, this
mixture instantly became of a bright purple: and I have found, by other
experiments, that the smallest quantity of salt of steel shews itself
as readily in the chyle by galls, as in any other liquor of the same
consistence.
This experiment (which was as fair as could have been desired),
together with another observation I have made, _viz._ that neither the
blood nor urine of patients, during the use of salt of steel, in the
least change colour with galls, renders it more than probable, that
this salt _does not enter the blood_.
As the salt was found to have undergone no change in the small guts,
it appears, that it is not prevented from entering the lacteals by its
being decomposed or precipitated, as has been imagined; but, on the
contrary, that what renders it incapable of being received by these
vessels, is its _astringency_: for the lacteals seem to be endowed with
that admirable faculty of admitting such particles of pure chyle as
they happen to be in contact with, and of accommodating their diameters
to them, at the same time that by their natural irritability, and
power of constriction they obstinately exclude such as are astringent;
which, were they to enter the lacteals, would either produce dangerous
obstructions in these vessels, or, if they got into the blood, would
occasion polypous concretions in the larger vessels, or coagulations
incapable of being transmitted thro’ the minute vessels of the lungs;
the effects of which would be either sudden death, or at least
inflammations and suppurations from obstructions in the pulmonary
vessels; inconveniences, which nature, by precluding astringents from
entering the lacteals, has carefully and wisely avoided.
Salt of steel, taken internally, must retain its astringency until it
be precipitated; which can scarce ever fail to happen in the great
guts, from the putrid _fæces_ they contain, which are always observed
to be tinged of a black colour from the metallic basis of the salt,
part of which, as it has little or no astringency, may, no doubt,
enter the blood, as Signor Menghini observed of the _crocus_, which
is the same substance; and we know, from the experiments of Lister
and Musgrave[35], that particles much grosser than those of the white
chyle, provided they be not astringent, or very acrid, are conveyed by
the lacteals. But the metallic basis being separated from its acid, and
thus reduced to a mere calx or earth, can scarce be supposed to have
any medicinal quality whatsoever, or at least to have any share in the
virtues justly attributed to salt of steel.
As this salt is not only astringent, and consequently a strengthener,
but at the same time acts with a gentle _stimulus_, all its virtues
(which are known to be very great in diseases, where the fluids are
either viscid, cold, and phlegmatic, or dissolved and watery, from a
laxity of the solids) may be accounted for from its immediate effects
on the stomach and _primæ viæ_, and on the system of the solids in
general by consent; which it would be needless to illustrate by similar
examples, because well known to every one the least versed in medical
studies. I shall therefore only beg leave, from the obvious qualities
of this medicine, and from what has been observed above, to deduce the
following corollaries.
1. That salt of steel has no deobstruent or aperient virtue by any
immediate action, that it can possibly have on the blood, or other
animal fluids, as some have imagined; but that, on the contrary, it
owes this quality to its _not entering the blood_, which it would
otherwise coagulate, and to _its action on the solids alone_.
2. That in diseases proceeding from a laxity of the solids, great care
ought to be taken to restore and invigorate the _primæ viæ_; since a
medicine (and this we may presume not the only one) whose immediate
action is confined to those parts, is yet found by experience to
produce so salutary effects in such diseases.
3. That as this salt does not enter the blood, and consequently cannot
be in danger of too much stimulating or constricting the vessels, on
which it only acts by consent, it may, in small doses, be successfully
used in many cases, where it has been imagined to be hurtful,
particularly in consumptions of the lungs, so frequent and fatal in
this island; which are commonly attended with too great a laxity of
the _primæ viæ_, and of the solids in general, tho’ they seem more
immediately to proceed from a laxity and weakness of the pulmonary
vessels; in which circumstances it must be of the utmost consequence
to restore the tone of those principal organs of chylification, the
_primæ viæ_; as good chyle not only corrects the acrimony of the blood,
which in the advanced stages of consumptions so much prevails, but
likewise saves a great deal of labour, which the lungs (already too
much oppressed) must otherwise undergo from a crude and ill-concocted
chyle. Agreeably to this we find, in the _Essays Physical and Literary_
of Edinburgh[36], two well-vouched histories of patients far gone in
consumptions, with the usual symptoms of pain in the breast, cough,
gross spitting of fetid matter, difficulty of breathing, hectic fits,
and morning sweats, perfectly cured in a few weeks, by the use of the
Hartfell-Spaw near Moffat; which, contrary to what is observed in most
natural chalybeat waters, contains a fixed vitriol of iron.
These, Sir, are the few observations I had to make at present on this
subject. I have taken the liberty to address them to you, in order, if
you shall think proper, to be communicated to your illustrious Society;
which, I hope, will continue to latest posterity those interesting
researches for the advancement of every branch of natural knowlege, by
which it has already acquired so much and so deserved honour; and am,
with the greatest respect,
SIR,
Your most obedient humble Servant,
Edward Wright.
Strand, Feb. 28. 1758.
LXXX. _A Dissertation on the Antiquity of Glass in Windows. In a Letter
to the Rev._ Tho. Birch, _D. D. Secret. R. S. By the Rev._ John Nixon,
_M. A. F.R.S._
[Read Mar. 2, 1758.]
London, March 2. 1758.
Dear Sir,
I Had the honour last winter to lay before the Royal Society a few
observations upon some of the curiosities found at Herculaneum,
_&c._[37]. Among other articles, I just mentioned a piece of a plate
of white glass; and now beg leave to inquire into the uses, to which
such plates might be applied in the early age, to which this fragment
undoubtedly belongs.
And here a person, who forms his ideas of ancient customs by what
he sees practised in later times, may be ready to offer several
conjectures; in some of which he will, probably, be mistaken; as in
others he may be justified by the genuine evidences of antiquity.
And, first, It is obvious to imagine, that such plates might serve
for _specula_, or looking-glasses. And, indeed, that _specula_ were
anciently made, not only of metals, and some stones, as the[38]
phengites, _&c._ but also of glass, may, I think, be collected from
Pliny, who, having mentioned the city of Sidon as formerly famous for
glass-houses, adds immediately afterwards, _Siquidem etiam specula
excogitaverat_[39]. But then it is to be observed, that before the
application of quicksilver in the constructing of these glasses (which,
I presume, is of no great antiquity), the reflection of images by such
_specula_ must have been effected by their being besmeared _behind_,
or tinged _thro’_ with some dark colour, especially black, which would
obstruct the refraction of the rays of light[40]. Upon these hypotheses
(supposing the tincture to be given after fusion) the _lamina_ before
us may be allowed to be capable of answering the purpose here assigned.
It may further be suggested, that plates of this kind might be intended
to be wrought into lens’s, or convex glasses, either for burning, or
magnifying objects placed in their focus. But this designation cannot
be supported by proper vouchers from antiquity. On the contrary, we
are informed, that the ancients used either _specula_[41] of metal, or
balls[42] of glass for the former of these purposes; as it is well
known, that glass was not applied to the latter, in optical uses, till
the beginning of the XIIIth century[43].
However, we may with greater probability propose another use, for
which the ancients might employ such plates of glass, as are now under
consideration, _viz._ the adorning the walls of their apartments by
way of wainscot. This I take to be the meaning of the _vitreæ cameræ_
mentioned by Pliny[44]; who intimates, that this fashion took its rise
from glass being used by M. Scaurus[45] for embellishing the scene
of that magnificent theatre, which he erected for exhibiting shows
to the Roman people in his ædileship[46]. And we may collect from
the same author[47] (what is further confirmed by his contemporary
[48]Seneca), that this kind of ornament had been admitted, in his
time, into chambers in houses, baths, _&c._ Whether the plates used for
this purpose were stained with various colours (as mentioned above),
or had tints of divers kinds applied to the back part of them, I shall
not pretend to determine: but in either way they would have a very
agreeable effect.
The last destination, which the obvious congruity of the thing itself,
countenanced by the practice of many ages past, as well as of the
present time, would induce one to ascribe to such plates of glass, is
that of windows for houses, baths, portico’s, _&c._ But I am sensible,
that whoever should be hardy enough to advance such an hypothesis,
would be censured as an innovator, in opposing the general opinion of
the connoisseurs in antiquity. These gentlemen are almost unanimous in
asserting, that whenever we meet with mention made of _specularia_ in
ancient writers (especially those _of_, or near _to_, the age, to which
we must refer this fragment), we are to understand by that term nothing
but fences made of _laminæ_, either of a certain stone called from its
transparent quality _lapis specularis_[49], brought first from Hispania
Citerior, and afterwards found in Cyprus, Cappadocia, Sicily, and
Africa; or of another stone of the same nature, _viz._ the phengites.
These, tho’ expressly distinguished from each other by Pliny[50],
are yet reckoned by some moderns[51] as one and the same thing; and
thought to have been nothing but a kind of white transparent talc, of
which (according to Mons.[52] Valois) there is found a great quantity
in Moscovy at this day.
Now that this _lapis specularis_, or phengites, was really used for
windows by the ancient Romans in their houses, _&c._ cannot be denied;
since (according to the opinion of the learned[53] in antiquity) this
usage is mentioned by Seneca[54] among other improvements in luxury
introduced in his time. But whether it was so used exclusive of other
materials (particularly glass), may, I think, admit a doubt. Salmasius
is of opinion[55], that nothing can be determined upon this point from
the word _specular_ itself, which seems to be a generical term, equally
applicable to windows of all kinds, whether consisting of the _lapis
specularis_, or any other transparent substance.
And as (according to this learned writer) there is nothing in the term
_specular_ itself, which hinders it from being extended to windows made
of other materials besides those above-mentioned; so others imagine,
that there are some intimations in ancient authors, which require, that
it should actually be so extended. Thus Mr. Castells, the ingenious
illustrator of the villa’s of the ancients, thinks[56], that “if this
had not been the case, Palladius would not have given directions to his
husbandman to make _specularia_ in the _olearium_[57], or store-room,
where the olives were preserved. For it appears (says this author) from
Pliny’s describing a temple[58] built of the _lapis specularis_, or
phengites, as the greatest rarity in his time, and the mention Plutarch
makes of a room in Domitian’s palace lined with it, that it was not
common enough for husbandmen to purchase;” _viz._ in such quantities,
as were required for the purposes mentioned above.
I shall not take upon me to decide upon the weight of this argument of
Mr. Castells; but only observe, that if any one should be induced by
it to think, that the use of glass for windows may be of much greater
antiquity than is commonly allowed, or even as old as the fragment,
which occasions these remarks, he may find other probable reasons to
corroborate his opinion. As, first, that there seems to have been a
natural and obvious transition from the practice of using glass plates
for the ornamenting the walls of apartments to that of introducing
light into those apartments, (as we find the _lapis specularis_
was in fact employed at the same time for both those purposes) and
consequently it seems reasonable to suppose, that the latter of these
applications could not be long in point of time after the former.
But it appears from the authorities produced above, that the former
of these usages did actually subsist in the age[59] of Pliny; and
therefore before the destruction of Herculaneum, where he lost his
life[60]. From whence we may draw no improbable conclusion, that the
latter destination of plates of glass, (_viz._ for window-fences) did
likewise precede the same event.
Give me leave to add further, that this presumptive argument in
favour of the antiquity of windows made of plates of glass receives
an additional force from the close relation, which must be allowed to
subsist between them, and those composed of the _lapis specularis_. The
former must be looked upon as an improvement upon the other, as they
answered all the purposes of convenience, and at the same time were
more beautiful; and being the manufacture[61] of Italy, might probably
be purchased at a less expence. Upon all which accounts it seems
reasonable to conclude, that one of these inventions would naturally be
introductory to the other: and consequently, that as window-lights of
the _lapis specularis_ began to be used within the memory of Seneca,
who died[62] under Nero, about _anno Christi_ 68. (_Helvic._), the
original of those of glass may have fair pretensions to a place within
the period assigned in the foregoing paragraph, _viz._ some years
before the destruction[63] of Herculaneum, in whose ruins the plate
before us was buried.
To conclude: I need not observe to you, that all the evidence here
produced to prove the usage of glass-windows to have been coæval
with the fragment we are now considering, is of the conjectural kind
only: for, I must confess, I have not been able to trace it up by any
positive authority higher than about 200 years short of the epocha last
mentioned, _viz._ to the latter end of the third century[64], when
it is expresly mentioned by Lactantius in these words:--_Manifestius
est, mentem esse, quæ per oculos ea, quæ sunt opposita, transpiciat,
quasi per fenestras lucente vitro aut speculari lapide obductas._--De
opificio Dei, cap. v.