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ink。
〃2d。 The application of a thin layer of gum； of
starch； or farina； of gelatine； or fish…glue； with a
view of sizing certain parts of the paper； or of
causing certain bodies to adhere to it momentarily；
is detected by an action similar to that which
shows paper to have lately been wetted by the contact
of liquids。
〃3d。 The heterogeneousness of the pulp of the
papers； and the kind of size with which they are
impregnated； lead to differences in the results
which are observed with the same chemical reagents。
We shall now examine each of these propositions；
and describe the means which we have
employed in endeavoring to solve questions of so
high a degree of interest。
〃1st。 The homogeneousness of sized paper not
partially altered by the contact of liquids （water；
alcohol； salt…water； vinegar； saliva； tears； urine；
acid salts； and alkaline salts） is demonstrated by
the uniform coloration which this surface takes on
being exposed； if not wholly； at least in various
parts； to the action of the vapor of iodine disengaged
at the ordinary temperature from a flask
containing a portion of the metalloid。 When the
surface of paper not stained by any of the above
mentioned liquids is exposed to the action of this
vapor for three or four minutes in a room the temperature
of which is about 60 degrees F。； a uniform yellowish；
or light…brownish yellow； coloration is noticed
on the whole extent exposed to the vapor of
iodine； in the contrary case； the surface which has
been moistened； and afterwards dried in the open
air； is perfectly distinguished by a different and
well circumscribed tint。 On the papers into which
paste starch and resin have been introduced； the
stains present such delicate reactions that we may
sometimes distinguish by their color the portion of
paper which has been moistened with alcohol from
that which has been moistened with water。 The
stain produced by alcohol takes a bistre…yellow
tint； that formed by water is colored of a more or
less deep violet blue； the desiccation having been
effected at the ordinary temperature。 For the
stains occasioned on these same papers by other
aqueous liquids； the tint； apart from its intensity；
resembles that of the stains of pure water。 The
feeble or dilute acids act like water on the surface
of the same paper containing starch in its paste；
but the concentrated mineral acids； by altering
more or less the substances which enter into the
composition of the latter； give test to the stains
which present differences。 We are always able
to recognize by the action of the vapor of iodine
the parts of the paper which have been put in
contact with chemical agents； the energy of which
has been arrested by washing in cold water。 We
are able； on several ancient deeds； written on
stamped paper； and a few words of which had
been removed by us with chemical agents； to
recognize the places where their action was exerted；
to see and to measure the extent which they occupied
on the surface of the paper。
〃The testing of a paper with the vapor of
iodine will present this double advantage over the
methods hitherto practiced for detecting falsifications
in writings； that it points out at once the
place in the paper in which any alteration may be
suspected； and that； on the other hand； it enables
us to act afterwards with the reagents proper for
causing the reappearance of the traces of ink； when
that is possible。 If the means which we now propose
cannot always make the former writing
appear； they demonstrate the places where the
alterations must have been made； when； however；
the want of uniformity presented by the surface
of the paper is not explained by any circumstance。
This proof becomes； therefore； a weapon which
the guilty person cannot avoid。 But might not
the presence of a stain； or several stains； developed
by the vapor of iodine； in different parts of a public
or private deed； give rise to a suspicion； where
these stains have； perhaps； been occasioned by the
spilling of some liquid on the surface of the paper？
and would it not be rash and unjust to raise an
accusation from such a fact？ There would indeed
be great temerity in drawing such a conclusion
from a fortuitous circumstance； but the inference
which may be drawn from the place occupied by
these stains on the surface of the paper； from the
more or less significant words found in those places；
would not permit an accusation to be so lightly
brought； where simple reasoning would be sufficient
to destroy its basis。 Besides； the subsequent reactions
which would be made would certainly never
revive words formerly written and effaced； whilst
the latter effects may be often produced； more or
less visibly； on those parts of the paper on which
falsification has been practiced； figures or words
being substituted for other figures or words。
〃2d。 The applications made to the surface of
a sheet of paper； with a view of covering it again
at certain parts with a fine layer of gum； gelatine；
starch or flour paste； or in other places to cause
other sheets of paper to adhere； may be recognized
not only by the reflection of light falling upon the
paper inclined at a certain degree of obliquity； and
by the transmission of light through the paper；
but also by the varying action which the vapor of
iodine exerts on the surface which is not homogeneous。
Papers containing starch and resin are
more powerfully acted upon by this vapor than
papers of a less complex composition。 Both in
the parts covered with starch； or paste flour； are
colored in a few minutes of a violet blue； but
with starched papers alone a more intense coloration
is manifest on the places covered again with a
thin layer of gum arabic； size or gelatine。 By
looking； then； on the surface of the paper； held
somewhat obliquely to incidental light； we distinguish
clearly； by their different aspects； the parts
on which these various substances have been
applied。 The vapor of iodine； in condensing at
the ordinary temperature on the surface of the
papers to which any kind of size has been applied
in various places； produces differences which are
most commonly well recognized by the greater or
less transparence of the paste of the paper。
3d。 The heterogeneousness of the pulp of the
various papers of commerce； and the nature of
the size with which they are penetrated； cause
differences； either in the coloration which the surface
of these papers takes when exposed to the
vapor of iodine； or in the tint which is manifested
in the portions of the size deposited in certain
portions of that surface； thus； papers with starched
pulp generally turn brown； or blue； according to
the amount of water that remains in their interstices；
other papers turn yellow only under the
influence of the vapor of iodine； and the parts
which have received superficially a layer of another
agglutinative body resist this action for a certain
time； and are distinguished from the parts of the
paper which are not covered with it。〃
My own investigations confirm to a great extent
the value of these experiments and the accuracy of
the deductions； in so far as they relate to 〃linen〃
paper； but they do not always obtain when made in
connection with paper of inferior grades。
It is also true that dry paper is affected differently
under the influence of the vapor of iodine； as would
be paper which had been moistened and then dried；
but the part which had been moist assumes the color
of blue…violet； while unaltered paper assumes a yellow…
brown color。 Even when the paper thus treated is
moistened all over with water； there will be a difference；
for those parts which had been before moistened；
will appear a dark violet…blue； while the other parts
will show a plain blue coloration。
In cases where pencil writing has been removed
with a soft rubber or fresh bread； the parts thus
erased will assume； when subjected to iodine fumes； a
brown color trending towards violet and much darker
than the undisturbed portions of the paper。 Lines
impressed upon paper with a 〃stylus；〃 a glass or
ordinary dry pen； can be made visible by the fumes of
iodine； the lines showing with a stronger coloration
than the surrounding paper。
CHAPTER XX。
FUGITIVE INK。
SOME OBSERVATIONS ABOUT 〃ADDED〃 COLOR TO INK
INVENTION OF COAL TAR COLORSCHRONOLOGICAL HISTORY
OF THE 〃ANILINES〃 EMPLOYED AS INKOTHER
SUBSTANCES USED FOR THE SAME PURPOSE。
THE term 〃added color；〃 as applied to ink； is the
popular phraseology for a multitude of materials
which have been more or less utilized for a period of
centuries； in adulterating and coloring ink。 In olden
times they were introduced into ink with an honest
belief that it would also improve and ensure its lasting
qualities； but latterly more often to cheapen the
cost of