19. CHAPTER XIX.
FRAUDULENT INK BACK GROUNDS.
DETECTION OF ALTERATIONS IN DOCUMENTS BY CHEMICAL TESTS WHICH APPLY
SOLELY TO THE PAPER—ACCURACY OF RESULTS OBTAINED BY USE OF IODINE
EXCELS THAT OF ALL OTHER CHEMICALS—IT APPLIES BEST TO LINEN
PAPER—MODERN HARD PAPER DOES NOT GIVE COMPLETE INFORMATION—EFFECT OF
IODINE ON MARKS MADE BY A STYLUS OR GLASS PEN.
FIFTY years ago and long before the employment of the fugitive
"anilines" for ink uses, and "wood pulp" as a material for paper, two
French chemists, Chevallier and Lassiagne, published in
the Journal de Chimie Médical, an article "On the Means to
be Employed for Detecting and Rendering Perceptible Fraudulent
Alterations in Public and Private Documents," which as translated is
valuable enough to quote in full:
"The numerous experiments which have been already tried at
various times, have made known the processes which may frequently be put
in practice for causing the reappearance of traces of writing effaced by
chemical reactions, and for throwing light on the work of the guilty.
But there are cases in which all the means proposed for this purpose
fail, and then the criminal may escape justice from the want of
conclusive material proofs. If, as has already been proved, it is not
always possible to cause the reappearance of the effaced writing, for
which written words have with a fraudulent intent been substituted, at
least, as our
experiments demonstrates, we may recognize, by some effects which are
manifest on the surface of the altered paper, the places where the
criminal act has been performed, circumscribe them by a simple chemical
reaction visible to the least practiced eye, and even measure their
extent. In a word, the visible alterations produced on a deed are
susceptible, owing to the partial modifications which the surface of the
paper has undergone, of being differently affected by certain chemical
actions, and of being rendered visible. The following experiments, made
in a judicial investigation, furnish us with the following facts:
"1st. The surface of paper sized in the ordinary way, or
letter paper, no longer presents with certain reactions, the same
uniformity where it has been either accidently moistened in several
places by various liquids, or left in contact for a certain time with
agents capable of removing or destroying the characters which have been
traced on it with 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° 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.