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vinegar impregnated with saturn。
〃Take an ounce of quick…lime； and half an ounce of
orpin； powder and mix them； put your mixture into
a matrass； and pour upon it five or six ounces of water；
that the water may be three fingers breadth above
the powder； stop your matrass with cork； wax； and a
bladder； set it in digestion in a mild sand heat ten or
twelve hours； shaking the matrass from time to time；
then let it settle； the liquid becomes clear like common
water。
〃Burn cork； and quench it in aqua vitae； then dissolve
it in a sufficient quantity of water； wherein you
shall have melted a little gumm arabick； in order to
make an ink as black as common ink。 You must
separate the cork that can't dissolve； and if the ink be
not black enough； add more cork as before。
〃Get the impregnation of saturn made with vinegar；
distilled as I have shewn before； or else dissolve
so much salt of saturn as a quantity of water
is able to receive： write on paper with a new
pen dipt in this liquor； take notice of the place
where you writ； and let it dry； nothing at all will
appear。
〃Write upon the invisible writing with the ink
made of burnt cork； and let it dry； that which you
have writ will appear as if it had been done with common
ink。
〃Dip a little cotton in the first liquor made of lime
and orpin； but the liquor must be first settled and
clear； rub the place you writ upon with this cotton
and that which appeared will presently disappear； and
that which was not seen will appear。
ANOTHER EXPERIMENT。
Take a book four fingers breadth in bigness； or
bigger if you will： write on the first leaf with your
impregnation of saturn； or else put a paper that you
have writ upon between the leaves； turn to t' other
side of the Book； and having observed as near as may
be the opposite place to your writing； rub the last leaf
of the book with cotton dipt in liquor made of quick…
lime and orpin； nay and leave the cotton on the place
clap a folded paper presently upon it； and shutting
the book quickly； strike upon it with your hand four
or five good strokes； then turn the book； and clap it
into a press for half a quarter of an hour； take it out
and open it； you'll find the place appear black； where
you had writ with the invisible ink。 The same thing
might be done through a wall； if you could provide
something to lay on both sides； that might hinder the
evaporation of the spirits。
REMARKS。
〃These operations are indeed of no use； but because
they are somewhat surprizing； I hope the curious will
not take it ill； that I make this small digression。
〃It is a hard matter to explicate well the effects I
have now related； nevertheless I shall endeavour to
illustrate them a little； without having recourse to
sympathy and antipathy； which are general terms； and
do not explicate nothing at all； but before I begin； we
must remark several things。
〃The first is； that it is an essential point to quench
the coal of cork in aqua vitae； that the visible ink may
become black with it。
〃Secondly； that the blackness of this ink does
proceed from the fuliginosity or sooty part of the coal
of the cork which is exceeding porous and light； and
that this fuliginosity is nothing but an oil very much
rarefied。
〃Thirdly； that the impregnation of saturn； which
makes the invisible ink； is only a lead dissolved； and
held up imperceptibly in an acid liquor； as I have said；
when I spoke of this metal。
〃Fourthly； that the first of these liquors in a mixture
of the alkali and igneous parts of quick…lime with
the sulphureous substance of arsenick； for the orpin
is a sort of arsenick； as I said before。
〃All this being granted； as no body can reasonably
think otherwise； I now affirm； that the reason why the
visible ink does disappear； when the defacing liquor is
rubbed upon it； is that this liquor consisting of an
alkali salt； and parts that are oily and penetrating；
this mixture does make a kind of soap； which is able
to dissolve any fuliginous substance； such as burnt
cork； especially when it has been already rarefied and
disposed for dissolution by aqua vitae； after the same
manner as common soap； which is compounded of oil；
and an alkali salt； is able to take away any spots made
by grease。
〃But it may be demanded； why after the dissolution
the blackness does disappear。
〃I answer； that the fuliginous parts have been so
divided； and locked up in the sulphureous alkali of
the liquor； that they are become invisible； and we see
every day that very exact solutions do render the thing
dissolved imperceptible； and without colour。
〃The little alkali salt which is in the burnt cork
may also the better serve to joyn with the alkali of
the quick…lime； and to help the dissolution。
〃As for the invisible ink； it is easy to apprehend
how that appears black； when the same liquor； which
serves to deface the other； is used upon it。 For whereas
the impregnation of saturn is only a lead suspended by
the edges； of the acid liquor； this lead must needs revive；
and resume its black colour； when that which held it
rarefied is entirely destroyed； so the alkali of quick…
lime being filled with the sulphurs of arsenick becomes
very proper to break and destroy the acids； and to
agglutinate together the particles of lead。
It happens that the visible ink does disappear by
reason that the parts which did render it black have
been dissolved； and the invisible ink does also appear
because the dissolved parts have been revived。
〃Quick…lime and； orpiment being mixed and digested
together in water； do yield a smell much like
that which happens when common sulphur is boiled in
a lixivium； of tartar。 This here is the stronger； because
the sulphur of arsenick is loaded with certain salts
that make a stronger impression on the smell。 Quick…
lime is an alkali that operates in this much like the
salt of tartar in the other operation； you must not
leave the matrass open； because the force of this
water doth consist in a volatile。
〃The lime retains the more fixt part of the arsenick
and the sulphurs that come forth are so much the
more subtile； as they are separated from what did fix
them before； and this appears to be so； because the
sulphurs must of necessity pass through all the book to
make a writing of a clear and invisible liquor appear
black and visible： and to facilitate this penetration the
book is strook； and then turned about； because the spirit
or volatile sulphurs do always tend upwards； you must
likewise clap it into a press； that these sulphurs may
not be dispersed in the air。 I have found； if that these
circumstances are not observed； the business fails。
Furthermore that which persuades me that the sulphurs
do pass through the book； and not take a circuit
to slip in by the sides； as many do imagine； is
that after the book is taken out of the press； all the
inside is found to be scented with the smell of this
liquor。
〃There is one thing more to be observed； which is；
that the infusion of quick…lime and orpin be newly
made； because otherwise it will not have force enough
to penetrate。 The three liquors should be made in
different places too； for if they should approach near
one another； they would be spoiled。
〃This last effect does likewise proceed from the defacing
liquor； for because upon the digestion of quick…
lime and orpin； it is a thing impossible for some of the
particles will exalt； stop the vessel as close as you
will； the air impregnated with these little bodies does
mix with； and alter the inks； insomuch that the visible
ink does thereby become the less black； and the invisible
ink does also acquire a little blackness。〃
Priceless MSS。 in immense number written in
periods between the third and thirteenth centuries
have been destroyed by modern scholars in experimentations
based on the false theory that the faded
inks on them； whether above or below other inks
（palimpsests）； contained iron。
Sulphocyanide of potassium is highly esteemed as a
reagent for the restoration of writing； if iron is present。
Theoretically； it is one of the best for such a purpose
if employed with acetic acid。 It causes； however； such
a decided contraction of parchment as to be utterly
useless； but for paper MSS。 is excellent。 The metallic
sulphides generally pronounced harmless； causes
the writing to soften and become illegible in a short
time。 On the other hand； yellow prussiate of potash；
with acetic acid in successive operations is of great
service in treating the most perplexing palimpsests。
Ink which badly corrodes a steel pen need not
necessarily be condemned； it may contain just the qualities
which make it bind to the paper and render it
more durable。
Some inks which are fairly permanent against time
if not tampered with； ca